parallel - build and execute shell command lines from standard input in parallel
parallel [options] [command [arguments]] < list_of_arguments parallel [options] [command [arguments]] ( ::: arguments | :::+ arguments | :::: argfile(s) | ::::+ argfile(s) ) ... parallel --semaphore [options] command #!/usr/bin/parallel --shebang [options] [command [arguments]] #!/usr/bin/parallel --shebang-wrap [options] [command [arguments]]
PARALLEL(1) parallel PARALLEL(1)
NAME
parallel - build and execute shell command lines from standard input in
parallel
SYNOPSIS
parallel [options] [command [arguments]] < list_of_arguments
parallel [options] [command [arguments]] ( ::: arguments | :::+
arguments | :::: argfile(s) | ::::+ argfile(s) ) ...
parallel --semaphore [options] command
#!/usr/bin/parallel --shebang [options] [command [arguments]]
#!/usr/bin/parallel --shebang-wrap [options] [command [arguments]]
DESCRIPTION
STOP!
Read the Reader's guide below if you are new to GNU parallel.
GNU parallel is a shell tool for executing jobs in parallel using one
or more computers. A job can be a single command or a small script that
has to be run for each of the lines in the input. The typical input is
a list of files, a list of hosts, a list of users, a list of URLs, or a
list of tables. A job can also be a command that reads from a pipe. GNU
parallel can then split the input into blocks and pipe a block into
each command in parallel.
If you use xargs and tee today you will find GNU parallel very easy to
use as GNU parallel is written to have the same options as xargs. If
you write loops in shell, you will find GNU parallel may be able to
replace most of the loops and make them run faster by running several
jobs in parallel.
GNU parallel makes sure output from the commands is the same output as
you would get had you run the commands sequentially. This makes it
possible to use output from GNU parallel as input for other programs.
For each line of input GNU parallel will execute command with the line
as arguments. If no command is given, the line of input is executed.
Several lines will be run in parallel. GNU parallel can often be used
as a substitute for xargs or cat | bash.
Reader's guide
GNU parallel includes the 4 types of documentation: Tutorial, how-to,
reference and explanation.
Tutorial
If you prefer reading a book buy GNU Parallel 2018 at
https://www.lulu.com/shop/ole-tange/gnu-parallel-2018/paperback/product-23558902.html
or download it at: https://doi.org/10.5281/zenodo.1146014 Read at least
chapter 1+2. It should take you less than 20 minutes.
Otherwise start by watching the intro videos for a quick introduction:
https://youtube.com/playlist?list=PL284C9FF2488BC6D1
If you want to dive deeper: spend a couple of hours walking through the
tutorial (man parallel_tutorial). Your command line will love you for
it.
How-to
You can find a lot of EXAMPLEs of use after the list of OPTIONS in man
parallel (Use LESS=+/EXAMPLE: man parallel). That will give you an idea
of what GNU parallel is capable of, and you may find a solution you can
simply adapt to your situation.
Reference
If you need a one page printable cheat sheet you can find it on:
https://www.gnu.org/software/parallel/parallel_cheat.pdf
The man page is the reference for all options.
Design discussion
If you want to know the design decisions behind GNU parallel, try: man
parallel_design. This is also a good intro if you intend to change GNU
parallel.
OPTIONS
command
Command to execute. If command or the following arguments contain
replacement strings (such as {}) every instance will be substituted
with the input.
If command is given, GNU parallel solve the same tasks as xargs. If
command is not given GNU parallel will behave similar to cat | sh.
The command must be an executable, a script, a composed command, an
alias, or a function.
Bash functions: export -f the function first or use env_parallel.
Bash, Csh, or Tcsh aliases: Use env_parallel.
Zsh, Fish, Ksh, and Pdksh functions and aliases: Use env_parallel.
{} Input line. This replacement string will be replaced by a full line
read from the input source. The input source is normally stdin
(standard input), but can also be given with -a, :::, or ::::.
The replacement string {} can be changed with -I.
If the command line contains no replacement strings then {} will be
appended to the command line.
Replacement strings are normally quoted, so special characters are
not parsed by the shell. The exception is if the command starts
with a replacement string; then the string is not quoted.
{.} Input line without extension. This replacement string will be
replaced by the input with the extension removed. If the input line
contains . after the last /, the last . until the end of the string
will be removed and {.} will be replaced with the remaining. E.g.
foo.jpg becomes foo, subdir/foo.jpg becomes subdir/foo,
sub.dir/foo.jpg becomes sub.dir/foo, sub.dir/bar remains
sub.dir/bar. If the input line does not contain . it will remain
unchanged.
The replacement string {.} can be changed with --er.
To understand replacement strings see {}.
{/} Basename of input line. This replacement string will be replaced by
the input with the directory part removed.
The replacement string {/} can be changed with --basenamereplace.
To understand replacement strings see {}.
{//}
Dirname of input line. This replacement string will be replaced by
the dir of the input line. See dirname(1).
The replacement string {//} can be changed with --dirnamereplace.
To understand replacement strings see {}.
{/.}
Basename of input line without extension. This replacement string
will be replaced by the input with the directory and extension part
removed. It is a combination of {/} and {.}.
The replacement string {/.} can be changed with
--basenameextensionreplace.
To understand replacement strings see {}.
{#} Sequence number of the job to run. This replacement string will be
replaced by the sequence number of the job being run. It contains
the same number as $PARALLEL_SEQ.
The replacement string {#} can be changed with --seqreplace.
To understand replacement strings see {}.
{%} Job slot number. This replacement string will be replaced by the
job's slot number between 1 and number of jobs to run in parallel.
There will never be 2 jobs running at the same time with the same
job slot number.
The replacement string {%} can be changed with --slotreplace.
If the job needs to be retried (e.g using --retries or
--retry-failed) the job slot is not automatically updated. You
should then instead use $PARALLEL_JOBSLOT:
$ do_test() {
id="$3 {%}=$1 PARALLEL_JOBSLOT=$2"
echo run "$id";
sleep 1
# fail if {%} is odd
return `echo $1%2 | bc`
}
$ export -f do_test
$ parallel -j3 --jl mylog do_test {%} \$PARALLEL_JOBSLOT {} ::: A B C D
run A {%}=1 PARALLEL_JOBSLOT=1
run B {%}=2 PARALLEL_JOBSLOT=2
run C {%}=3 PARALLEL_JOBSLOT=3
run D {%}=1 PARALLEL_JOBSLOT=1
$ parallel --retry-failed -j3 --jl mylog do_test {%} \$PARALLEL_JOBSLOT {} ::: A B C D
run A {%}=1 PARALLEL_JOBSLOT=1
run C {%}=3 PARALLEL_JOBSLOT=2
run D {%}=1 PARALLEL_JOBSLOT=3
Notice how {%} and $PARALLEL_JOBSLOT differ in the retry run of C
and D.
To understand replacement strings see {}.
{n} Argument from input source n or the n'th argument. This positional
replacement string will be replaced by the input from input source
n (when used with -a or ::::) or with the n'th argument (when used
with -N). If n is negative it refers to the n'th last argument.
To understand replacement strings see {}.
{n.}
Argument from input source n or the n'th argument without
extension. It is a combination of {n} and {.}.
This positional replacement string will be replaced by the input
from input source n (when used with -a or ::::) or with the n'th
argument (when used with -N). The input will have the extension
removed.
To understand positional replacement strings see {n}.
{n/}
Basename of argument from input source n or the n'th argument. It
is a combination of {n} and {/}.
This positional replacement string will be replaced by the input
from input source n (when used with -a or ::::) or with the n'th
argument (when used with -N). The input will have the directory (if
any) removed.
To understand positional replacement strings see {n}.
{n//}
Dirname of argument from input source n or the n'th argument. It
is a combination of {n} and {//}.
This positional replacement string will be replaced by the dir of
the input from input source n (when used with -a or ::::) or with
the n'th argument (when used with -N). See dirname(1).
To understand positional replacement strings see {n}.
{n/.}
Basename of argument from input source n or the n'th argument
without extension. It is a combination of {n}, {/}, and {.}.
This positional replacement string will be replaced by the input
from input source n (when used with -a or ::::) or with the n'th
argument (when used with -N). The input will have the directory (if
any) and extension removed.
To understand positional replacement strings see {n}.
{=perl expression=}
Replace with calculated perl expression. $_ will contain the same
as {}. After evaluating perl expression $_ will be used as the
value. It is recommended to only change $_ but you have full access
to all of GNU parallel's internal functions and data structures.
The expression must give the same result if evaluated twice -
otherwise the behaviour is undefined. E.g. this will not work as
expected:
parallel echo '{= $_= ++$wrong_counter =}' ::: a b c
A few convenience functions and data structures have been made:
Q(string) shell quote a string
pQ(string) perl quote a string
uq() (or uq) do not quote current replacement string
hash(val) compute B::hash(val)
total_jobs() number of jobs in total
slot() slot number of job
seq() sequence number of job
@arg the arguments
skip() skip this job (see also --filter)
yyyy_mm_dd_hh_mm_ss()
yyyy_mm_dd_hh_mm()
yyyy_mm_dd()
yyyymmddhhmmss()
yyyymmddhhmm()
yyyymmdd() time functions
Example:
seq 10 | parallel echo {} + 1 is {= '$_++' =}
parallel csh -c {= '$_="mkdir ".Q($_)' =} ::: '12" dir'
seq 50 | parallel echo job {#} of {= '$_=total_jobs()' =}
See also: --rpl --parens
{=n perl expression=}
Positional equivalent to {=perl expression=}. To understand
positional replacement strings see {n}.
See also: {=perl expression=} {n}.
::: arguments
Use arguments from the command line as input source instead of
stdin (standard input). Unlike other options for GNU parallel :::
is placed after the command and before the arguments.
The following are equivalent:
(echo file1; echo file2) | parallel gzip
parallel gzip ::: file1 file2
parallel gzip {} ::: file1 file2
parallel --arg-sep ,, gzip {} ,, file1 file2
parallel --arg-sep ,, gzip ,, file1 file2
parallel ::: "gzip file1" "gzip file2"
To avoid treating ::: as special use --arg-sep to set the argument
separator to something else. See also --arg-sep.
If multiple ::: are given, each group will be treated as an input
source, and all combinations of input sources will be generated.
E.g. ::: 1 2 ::: a b c will result in the combinations (1,a) (1,b)
(1,c) (2,a) (2,b) (2,c). This is useful for replacing nested for-
loops.
::: and :::: can be mixed. So these are equivalent:
parallel echo {1} {2} {3} ::: 6 7 ::: 4 5 ::: 1 2 3
parallel echo {1} {2} {3} :::: <(seq 6 7) <(seq 4 5) \
:::: <(seq 1 3)
parallel -a <(seq 6 7) echo {1} {2} {3} :::: <(seq 4 5) \
:::: <(seq 1 3)
parallel -a <(seq 6 7) -a <(seq 4 5) echo {1} {2} {3} \
::: 1 2 3
seq 6 7 | parallel -a - -a <(seq 4 5) echo {1} {2} {3} \
::: 1 2 3
seq 4 5 | parallel echo {1} {2} {3} :::: <(seq 6 7) - \
::: 1 2 3
:::+ arguments
Like ::: but linked like --link to the previous input source.
Contrary to --link, values do not wrap: The shortest input source
determines the length.
Example:
parallel echo ::: a b c :::+ 1 2 3 ::: X Y :::+ 11 22
:::: argfiles
Another way to write -a argfile1 -a argfile2 ...
::: and :::: can be mixed.
See -a, ::: and --link.
::::+ argfiles
Like :::: but linked like --link to the previous input source.
Contrary to --link, values do not wrap: The shortest input source
determines the length.
--null
-0 Use NUL as delimiter. Normally input lines will end in \n
(newline). If they end in \0 (NUL), then use this option. It is
useful for processing arguments that may contain \n (newline).
--arg-file input-file
-a input-file
Use input-file as input source. If you use this option, stdin
(standard input) is given to the first process run. Otherwise,
stdin (standard input) is redirected from /dev/null.
If multiple -a are given, each input-file will be treated as an
input source, and all combinations of input sources will be
generated. E.g. The file foo contains 1 2, the file bar contains a
b c. -a foo -a bar will result in the combinations (1,a) (1,b)
(1,c) (2,a) (2,b) (2,c). This is useful for replacing nested for-
loops.
See also: --link and {n}.
--arg-file-sep sep-str
Use sep-str instead of :::: as separator string between command and
argument files. Useful if :::: is used for something else by the
command.
See also: ::::.
--arg-sep sep-str
Use sep-str instead of ::: as separator string. Useful if ::: is
used for something else by the command.
Also useful if you command uses ::: but you still want to read
arguments from stdin (standard input): Simply change --arg-sep to a
string that is not in the command line.
See also: :::.
--bar
Show progress as a progress bar. In the bar is shown: % of jobs
completed, estimated seconds left, and number of jobs started.
It is compatible with zenity:
seq 1000 | parallel -j30 --bar '(echo {};sleep 0.1)' \
2> >(perl -pe 'BEGIN{$/="\r";$|=1};s/\r/\n/g' |
zenity --progress --auto-kill) | wc
--basefile file
--bf file
file will be transferred to each sshlogin before a job is started.
It will be removed if --cleanup is active. The file may be a script
to run or some common base data needed for the job. Multiple --bf
can be specified to transfer more basefiles. The file will be
transferred the same way as --transferfile.
--basenamereplace replace-str
--bnr replace-str
Use the replacement string replace-str instead of {/} for basename
of input line.
--basenameextensionreplace replace-str
--bner replace-str
Use the replacement string replace-str instead of {/.} for basename
of input line without extension.
--bin binexpr
Use binexpr as binning key and bin input to the jobs.
binexpr is [column number|column name] [perlexpression] e.g. 3,
Address, 3 $_%=100, Address s/\D//g.
Each input line is split using --colsep. The value of the column is
put into $_, the perl expression is executed, the resulting value
is is the job slot that will be given the line. If the value is
bigger than the number of jobslots the value will be modulo number
of jobslots.
This is similar to --shard but the hashing algorithm is a simple
modulo, which makes it predictible which jobslot will receive which
value.
The performance is in the order of 100K rows per second. Faster if
the bincol is small (<10), slower if it is big (>100).
--bin requires --pipe and a fixed numeric value for --jobs.
See also: --shard, --group-by, --roundrobin.
--bg
Run command in background thus GNU parallel will not wait for
completion of the command before exiting. This is the default if
--semaphore is set.
See also: --fg, man sem.
Implies --semaphore.
--bibtex
--citation
Print the citation notice and BibTeX entry for GNU parallel,
silence citation notice for all future runs, and exit. It will not
run any commands.
If it is impossible for you to run --citation you can instead use
--will-cite, which will run commands, but which will only silence
the citation notice for this single run.
If you use --will-cite in scripts to be run by others you are
making it harder for others to see the citation notice. The
development of GNU parallel is indirectly financed through
citations, so if your users do not know they should cite then you
are making it harder to finance development. However, if you pay
10000 EUR, you have done your part to finance future development
and should feel free to use --will-cite in scripts.
If you do not want to help financing future development by letting
other users see the citation notice or by paying, then please use
another tool instead of GNU parallel. You can find some of the
alternatives in man parallel_alternatives.
--block size
--block-size size
Size of block in bytes to read at a time. The size can be postfixed
with K, M, G, T, P, k, m, g, t, or p (see UNIT PREFIX).
GNU parallel tries to meet the block size but can be off by the
length of one record. For performance reasons size should be bigger
than a two records. GNU parallel will warn you and automatically
increase the size if you choose a size that is too small.
If you use -N, --block-size should be bigger than N+1 records.
size defaults to 1M.
When using --pipepart a negative block size is not interpreted as a
blocksize but as the number of blocks each jobslot should have. So
this will run 10*5 = 50 jobs in total:
parallel --pipepart -a myfile --block -10 -j5 wc
This is an efficient alternative to --roundrobin because data is
never read by GNU parallel, but you can still have very few
jobslots process a large amount of data.
See --pipe and --pipepart for use of this.
--blocktimeout duration
--bt duration
Time out for reading block when using --pipe. If it takes longer
than duration to read a full block, use the partial block read so
far.
duration must be in whole seconds, but can be expressed as floats
postfixed with s, m, h, or d which would multiply the float by 1,
60, 3600, or 86400. Thus these are equivalent: --blocktimeout
100000 and --blocktimeout 1d3.5h16.6m4s.
--cat
Create a temporary file with content. Normally --pipe/--pipepart
will give data to the program on stdin (standard input). With --cat
GNU parallel will create a temporary file with the name in {}, so
you can do: parallel --pipe --cat wc {}.
Implies --pipe unless --pipepart is used.
See also: --fifo.
--cleanup
Remove transferred files. --cleanup will remove the transferred
files on the remote computer after processing is done.
find log -name '*gz' | parallel \
--sshlogin server.example.com --transferfile {} \
--return {.}.bz2 --cleanup "zcat {} | bzip -9 >{.}.bz2"
With --transferfile {} the file transferred to the remote computer
will be removed on the remote computer. Directories on the remote
computer containing the file will be removed if they are empty.
With --return the file transferred from the remote computer will be
removed on the remote computer. Directories on the remote computer
containing the file will be removed if they are empty.
--cleanup is ignored when not used with --transferfile or --return.
--colsep regexp
-C regexp
Column separator. The input will be treated as a table with regexp
separating the columns. The n'th column can be accessed using {n}
or {n.}. E.g. {3} is the 3rd column.
If there are more input sources, each input source will be
separated, but the columns from each input source will be linked
(see --link).
parallel --colsep '-' echo {4} {3} {2} {1} \
::: A-B C-D ::: e-f g-h
--colsep implies --trim rl, which can be overridden with --trim n.
regexp is a Perl Regular Expression:
https://perldoc.perl.org/perlre.html
--compress
Compress temporary files. If the output is big and very
compressible this will take up less disk space in $TMPDIR and
possibly be faster due to less disk I/O.
GNU parallel will try pzstd, lbzip2, pbzip2, zstd, pigz, lz4, lzop,
plzip, lzip, lrz, gzip, pxz, lzma, bzip2, xz, clzip, in that order,
and use the first available.
--compress-program prg
--decompress-program prg
Use prg for (de)compressing temporary files. It is assumed that prg
-dc will decompress stdin (standard input) to stdout (standard
output) unless --decompress-program is given.
--csv
Treat input as CSV-format. --colsep sets the field delimiter. It
works very much like --colsep except it deals correctly with
quoting:
echo '"1 big, 2 small","2""x4"" plank",12.34' |
parallel --csv echo {1} of {2} at {3}
Even quoted newlines are parsed correctly:
(echo '"Start of field 1 with newline'
echo 'Line 2 in field 1";value 2') |
parallel --csv --colsep ';' echo Field 1: {1} Field 2: {2}
When used with --pipe only pass full CSV-records.
--ctag str
Color tag. See --tag.
--ctagstring str
Color tagstring. See --tagstring.
--delay mytime
Delay starting next job by mytime. GNU parallel will pause mytime
after starting each job. mytime is normally in seconds, but can be
floats postfixed with s, m, h, or d which would multiply the float
by 1, 60, 3600, or 86400. Thus these are equivalent: --delay 100000
and --delay 1d3.5h16.6m4s.
If you append 'auto' to mytime (e.g. 13m3sauto) GNU parallel will
automatically try to find the optimal value: If a job fails, mytime
is doubled. If a job succeeds, mytime is decreased by 10%.
--delimiter delim
-d delim
Input items are terminated by delim. Quotes and backslash are not
special; every character in the input is taken literally. Disables
the end-of-file string, which is treated like any other argument.
The specified delimiter may be characters, C-style character
escapes such as \n, or octal or hexadecimal escape codes. Octal
and hexadecimal escape codes are understood as for the printf
command. Multibyte characters are not supported.
--dirnamereplace replace-str
--dnr replace-str
Use the replacement string replace-str instead of {//} for dirname
of input line.
--dry-run
Print the job to run on stdout (standard output), but do not run
the job. Use -v -v to include the wrapping that GNU parallel
generates (for remote jobs, --tmux, --nice, --pipe, --pipepart,
--fifo and --cat). Do not count on this literally, though, as the
job may be scheduled on another computer or the local computer if :
is in the list.
-E eof-str
Set the end of file string to eof-str. If the end of file string
occurs as a line of input, the rest of the input is not read. If
neither -E nor -e is used, no end of file string is used.
--eof[=eof-str]
-e[eof-str]
This option is a synonym for the -E option. Use -E instead,
because it is POSIX compliant for xargs while this option is not.
If eof-str is omitted, there is no end of file string. If neither
-E nor -e is used, no end of file string is used.
--embed
Embed GNU parallel in a shell script. If you need to distribute
your script to someone who does not want to install GNU parallel
you can embed GNU parallel in your own shell script:
parallel --embed > new_script
After which you add your code at the end of new_script. This is
tested on ash, bash, dash, ksh, sh, and zsh.
--env var
Copy environment variable var. This will copy var to the
environment that the command is run in. This is especially useful
for remote execution.
In Bash var can also be a Bash function - just remember to export
-f the function, see command.
The variable '_' is special. It will copy all exported environment
variables except for the ones mentioned in
~/.parallel/ignored_vars.
To copy the full environment (both exported and not exported
variables, arrays, and functions) use env_parallel.
See also: --record-env, --session.
--eta
Show the estimated number of seconds before finishing. This forces
GNU parallel to read all jobs before starting to find the number of
jobs. GNU parallel normally only reads the next job to run.
The estimate is based on the runtime of finished jobs, so the first
estimate will only be shown when the first job has finished.
Implies --progress.
See also: --bar, --progress.
--fg
Run command in foreground.
With --tmux and --tmuxpane GNU parallel will start tmux in the
foreground.
With --semaphore GNU parallel will run the command in the
foreground (opposite --bg), and wait for completion of the command
before exiting.
See also: --bg, man sem.
--fifo
Create a temporary fifo with content. Normally --pipe and
--pipepart will give data to the program on stdin (standard input).
With --fifo GNU parallel will create a temporary fifo with the name
in {}, so you can do: parallel --pipe --fifo wc {}.
Beware: If data is not read from the fifo, the job will block
forever.
Implies --pipe unless --pipepart is used.
See also: --cat.
--filter filter
Only run jobs where filter is true. filter can contain replacement
strings and Perl code. Example:
parallel --filter '{1} < {2}+1' echo ::: {1..3} ::: {1..3}
Outputs: 1,1 1,2 1,3 2,2 2,3 3,3
--filter-hosts
Remove down hosts. For each remote host: check that login through
ssh works. If not: do not use this host.
For performance reasons, this check is performed only at the start
and every time --sshloginfile is changed. If an host goes down
after the first check, it will go undetected until --sshloginfile
is changed; --retries can be used to mitigate this.
Currently you can not put --filter-hosts in a profile, $PARALLEL,
/etc/parallel/config or similar. This is because GNU parallel uses
GNU parallel to compute this, so you will get an infinite loop.
This will likely be fixed in a later release.
--gnu
Behave like GNU parallel. This option historically took precedence
over --tollef. The --tollef option is now retired, and therefore
may not be used. --gnu is kept for compatibility.
--group
Group output. Output from each job is grouped together and is only
printed when the command is finished. Stdout (standard output)
first followed by stderr (standard error).
This takes in the order of 0.5ms per job and depends on the speed
of your disk for larger output. It can be disabled with -u, but
this means output from different commands can get mixed.
--group is the default. Can be reversed with -u.
See also: --line-buffer --ungroup
--group-by val
Group input by value. Combined with --pipe/--pipepart --group-by
groups lines with the same value into a record.
The value can be computed from the full line or from a single
column.
val can be:
column number Use the value in the column numbered.
column name Treat the first line as a header and use the value
in the column named.
(Not supported with --pipepart).
perl expression
Run the perl expression and use $_ as the value.
column number perl expression
Put the value of the column put in $_, run the perl
expression, and use $_ as the value.
column name perl expression
Put the value of the column put in $_, run the perl
expression, and use $_ as the value.
(Not supported with --pipepart).
Example:
UserID, Consumption
123, 1
123, 2
12-3, 1
221, 3
221, 1
2/21, 5
If you want to group 123, 12-3, 221, and 2/21 into 4 records and
pass one record at a time to wc:
tail -n +2 table.csv | \
parallel --pipe --colsep , --group-by 1 -kN1 wc
Make GNU parallel treat the first line as a header:
cat table.csv | \
parallel --pipe --colsep , --header : --group-by 1 -kN1 wc
Address column by column name:
cat table.csv | \
parallel --pipe --colsep , --header : --group-by UserID -kN1 wc
If 12-3 and 123 are really the same UserID, remove non-digits in
UserID when grouping:
cat table.csv | parallel --pipe --colsep , --header : \
--group-by 'UserID s/\D//g' -kN1 wc
See also: --shard, --roundrobin.
--help
-h Print a summary of the options to GNU parallel and exit.
--halt-on-error val
--halt val
When should GNU parallel terminate? In some situations it makes no
sense to run all jobs. GNU parallel should simply give up as soon
as a condition is met.
val defaults to never, which runs all jobs no matter what.
val can also take on the form of when,why.
when can be 'now' which means kill all running jobs and halt
immediately, or it can be 'soon' which means wait for all running
jobs to complete, but start no new jobs.
why can be 'fail=X', 'fail=Y%', 'success=X', 'success=Y%',
'done=X', or 'done=Y%' where X is the number of jobs that has to
fail, succeed, or be done before halting, and Y is the percentage
of jobs that has to fail, succeed, or be done before halting.
Example:
--halt now,fail=1 exit when the first job fails. Kill running
jobs.
--halt soon,fail=3 exit when 3 jobs fail, but wait for running
jobs to complete.
--halt soon,fail=3% exit when 3% of the jobs have failed, but
wait for running jobs to complete.
--halt now,success=1 exit when a job succeeds. Kill running jobs.
--halt soon,success=3 exit when 3 jobs succeeds, but wait for
running jobs to complete.
--halt now,success=3% exit when 3% of the jobs have succeeded.
Kill running jobs.
--halt now,done=1 exit when one of the jobs finishes. Kill
running jobs.
--halt soon,done=3 exit when 3 jobs finishes, but wait for
running jobs to complete.
--halt now,done=3% exit when 3% of the jobs have finished. Kill
running jobs.
For backwards compatibility these also work:
0 never
1 soon,fail=1
2 now,fail=1
-1 soon,success=1
-2 now,success=1
1-99% soon,fail=1-99%
--header regexp
Use regexp as header. For normal usage the matched header
(typically the first line: --header '.*\n') will be split using
--colsep (which will default to '\t') and column names can be used
as replacement variables: {column name}, {column name/}, {column
name//}, {column name/.}, {column name.}, {=column name perl
expression =}, ..
For --pipe the matched header will be prepended to each output.
--header : is an alias for --header '.*\n'.
If regexp is a number, it is a fixed number of lines.
--hostgroups
--hgrp
Enable hostgroups on arguments. If an argument contains '@' the
string after '@' will be removed and treated as a list of
hostgroups on which this job is allowed to run. If there is no
--sshlogin with a corresponding group, the job will run on any
hostgroup.
Example:
parallel --hostgroups \
--sshlogin @grp1/myserver1 -S @grp1+grp2/myserver2 \
--sshlogin @grp3/myserver3 \
echo ::: my_grp1_arg@grp1 arg_for_grp2@grp2 third@grp1+grp3
my_grp1_arg may be run on either myserver1 or myserver2, third may
be run on either myserver1 or myserver3, but arg_for_grp2 will only
be run on myserver2.
See also: --sshlogin, $PARALLEL_HOSTGROUPS,
$PARALLEL_ARGHOSTGROUPS.
-I replace-str
Use the replacement string replace-str instead of {}.
--replace[=replace-str]
-i[replace-str]
This option is a synonym for -Ireplace-str if replace-str is
specified, and for -I {} otherwise. This option is deprecated; use
-I instead.
--joblog logfile
Logfile for executed jobs. Save a list of the executed jobs to
logfile in the following TAB separated format: sequence number,
sshlogin, start time as seconds since epoch, run time in seconds,
bytes in files transferred, bytes in files returned, exit status,
signal, and command run.
For --pipe bytes transferred and bytes returned are number of input
and output of bytes.
If logfile is prepended with '+' log lines will be appended to the
logfile.
To convert the times into ISO-8601 strict do:
cat logfile | perl -a -F"\t" -ne \
'chomp($F[2]=`date -d \@$F[2] +%FT%T`); print join("\t",@F)'
If the host is long, you can use column -t to pretty print it:
cat joblog | column -t
See also: --resume --resume-failed.
--jobs N
-j N
--max-procs N
-P N
Number of jobslots on each machine. Run up to N jobs in parallel.
0 means as many as possible (this can take a while to determine).
Default is 100% which will run one job per CPU on each machine.
Due to a bug -j 0 will also evaluate replacement strings twice up
to the number of joblots:
# This will not count from 1 but from number-of-jobslots
seq 10000 | parallel -j0 echo '{= $_ = $foo++; =}' | head
# This will count from 1
seq 10000 | parallel -j100 echo '{= $_ = $foo++; =}' | head
If --semaphore is set, the default is 1 thus making a mutex.
--jobs +N
-j +N
--max-procs +N
-P +N
Add N to the number of CPUs. Run this many jobs in parallel. See
also --use-cores-instead-of-threads and
--use-sockets-instead-of-threads.
--jobs -N
-j -N
--max-procs -N
-P -N
Subtract N from the number of CPUs. Run this many jobs in
parallel. If the evaluated number is less than 1 then 1 will be
used. See also --use-cores-instead-of-threads and
--use-sockets-instead-of-threads.
--jobs N%
-j N%
--max-procs N%
-P N%
Multiply N% with the number of CPUs. Run this many jobs in
parallel. See also --use-cores-instead-of-threads and
--use-sockets-instead-of-threads.
--jobs procfile
-j procfile
--max-procs procfile
-P procfile
Read parameter from file. Use the content of procfile as parameter
for -j. E.g. procfile could contain the string 100% or +2 or 10. If
procfile is changed when a job completes, procfile is read again
and the new number of jobs is computed. If the number is lower than
before, running jobs will be allowed to finish but new jobs will
not be started until the wanted number of jobs has been reached.
This makes it possible to change the number of simultaneous running
jobs while GNU parallel is running.
--keep-order
-k Keep sequence of output same as the order of input. Normally the
output of a job will be printed as soon as the job completes. Try
this to see the difference:
parallel -j4 sleep {}\; echo {} ::: 2 1 4 3
parallel -j4 -k sleep {}\; echo {} ::: 2 1 4 3
If used with --onall or --nonall the output will grouped by
sshlogin in sorted order.
If used with --pipe --roundrobin and the same input, the jobslots
will get the same blocks in the same order in every run.
-k only affects the order in which the output is printed - not the
order in which jobs are run.
-L recsize
When used with --pipe: Read records of recsize.
When used otherwise: Use at most recsize nonblank input lines per
command line. Trailing blanks cause an input line to be logically
continued on the next input line.
-L 0 means read one line, but insert 0 arguments on the command
line.
recsize can be postfixed with K, M, G, T, P, k, m, g, t, or p (see
UNIT PREFIX).
Implies -X unless -m, --xargs, or --pipe is set.
--max-lines[=recsize]
-l[recsize]
When used with --pipe: Read records of recsize lines.
When used otherwise: Synonym for the -L option. Unlike -L, the
recsize argument is optional. If recsize is not specified, it
defaults to one. The -l option is deprecated since the POSIX
standard specifies -L instead.
-l 0 is an alias for -l 1.
Implies -X unless -m, --xargs, or --pipe is set.
--limit "command args"
Dynamic job limit. Before starting a new job run command with args.
The exit value of command determines what GNU parallel will do:
0 Below limit. Start another job.
1 Over limit. Start no jobs.
2 Way over limit. Kill the youngest job.
You can use any shell command. There are 3 predefined commands:
"io n" Limit for I/O. The amount of disk I/O will be computed as
a value 0-100, where 0 is no I/O and 100 is at least one
disk is 100% saturated.
"load n" Similar to --load.
"mem n" Similar to --memfree.
--line-buffer
--lb
Buffer output on line basis. --group will keep the output together
for a whole job. --ungroup allows output to mixup with half a line
coming from one job and half a line coming from another job.
--line-buffer fits between these two: GNU parallel will print a
full line, but will allow for mixing lines of different jobs.
--line-buffer takes more CPU power than both --group and --ungroup,
but can be much faster than --group if the CPU is not the limiting
factor.
Normally --line-buffer does not buffer on disk, and can thus
process an infinite amount of data, but it will buffer on disk when
combined with: --keep-order, --results, --compress, and --files.
This will make it as slow as --group and will limit output to the
available disk space.
With --keep-order --line-buffer will output lines from the first
job continuously while it is running, then lines from the second
job while that is running. It will buffer full lines, but jobs will
not mix. Compare:
parallel -j0 'echo {};sleep {};echo {}' ::: 1 3 2 4
parallel -j0 --lb 'echo {};sleep {};echo {}' ::: 1 3 2 4
parallel -j0 -k --lb 'echo {};sleep {};echo {}' ::: 1 3 2 4
See also: --group --ungroup
--xapply
--link
Link input sources. Read multiple input sources like xapply. If
multiple input sources are given, one argument will be read from
each of the input sources. The arguments can be accessed in the
command as {1} .. {n}, so {1} will be a line from the first input
source, and {6} will refer to the line with the same line number
from the 6th input source.
Compare these two:
parallel echo {1} {2} ::: 1 2 3 ::: a b c
parallel --link echo {1} {2} ::: 1 2 3 ::: a b c
Arguments will be recycled if one input source has more arguments
than the others:
parallel --link echo {1} {2} {3} \
::: 1 2 ::: I II III ::: a b c d e f g
See also --header, :::+, ::::+.
--load max-load
Do not start new jobs on a given computer unless the number of
running processes on the computer is less than max-load. max-load
uses the same syntax as --jobs, so 100% for one per CPU is a valid
setting. Only difference is 0 which is interpreted as 0.01.
--controlmaster
-M Use ssh's ControlMaster to make ssh connections faster. Useful if
jobs run remote and are very fast to run. This is disabled for
sshlogins that specify their own ssh command.
-m Multiple arguments. Insert as many arguments as the command line
length permits. If multiple jobs are being run in parallel:
distribute the arguments evenly among the jobs. Use -j1 or --xargs
to avoid this.
If {} is not used the arguments will be appended to the line. If
{} is used multiple times each {} will be replaced with all the
arguments.
Support for -m with --sshlogin is limited and may fail.
See also -X for context replace. If in doubt use -X as that will
most likely do what is needed.
--memfree size
Minimum memory free when starting another job. The size can be
postfixed with K, M, G, T, P, k, m, g, t, or p (see UNIT PREFIX).
If the jobs take up very different amount of RAM, GNU parallel will
only start as many as there is memory for. If less than size bytes
are free, no more jobs will be started. If less than 50% size bytes
are free, the youngest job will be killed, and put back on the
queue to be run later.
--retries must be set to determine how many times GNU parallel
should retry a given job.
See also: --memsuspend
--memsuspend size
Suspend jobs when there is less than 2 * size memory free. The size
can be postfixed with K, M, G, T, P, k, m, g, t, or p (see UNIT
PREFIX).
If the available memory falls below 2 * size, GNU parallel will
suspend some of the running jobs. If the available memory falls
below size, only one job will be running.
If a single job takes up at most size RAM, all jobs will complete
without running out of memory. If you have swap available, you can
usually lower size to around half the size of a single job - with
the slight risk of swapping a little.
Jobs will be resumed when more RAM is available - typically when
the oldest job completes.
--memsuspend only works on local jobs because there is no obvious
way to suspend remote jobs.
See also: --memfree
--minversion version
Print the version GNU parallel and exit. If the current version of
GNU parallel is less than version the exit code is 255. Otherwise
it is 0.
This is useful for scripts that depend on features only available
from a certain version of GNU parallel.
--max-args=max-args
-n max-args
Use at most max-args arguments per command line. Fewer than max-
args arguments will be used if the size (see the -s option) is
exceeded, unless the -x option is given, in which case GNU parallel
will exit.
-n 0 means read one argument, but insert 0 arguments on the command
line.
max-args can be postfixed with K, M, G, T, P, k, m, g, t, or p (see
UNIT PREFIX).
Implies -X unless -m is set.
--max-replace-args=max-args
-N max-args
Use at most max-args arguments per command line. Like -n but also
makes replacement strings {1} .. {max-args} that represents
argument 1 .. max-args. If too few args the {n} will be empty.
-N 0 means read one argument, but insert 0 arguments on the command
line.
This will set the owner of the homedir to the user:
tr ':' '\n' < /etc/passwd | parallel -N7 chown {1} {6}
Implies -X unless -m or --pipe is set.
max-args can be postfixed with K, M, G, T, P, k, m, g, t, or p (see
UNIT PREFIX).
When used with --pipe -N is the number of records to read. This is
somewhat slower than --block.
--nonall
--onall with no arguments. Run the command on all computers given
with --sshlogin but take no arguments. GNU parallel will log into
--jobs number of computers in parallel and run the job on the
computer. -j adjusts how many computers to log into in parallel.
This is useful for running the same command (e.g. uptime) on a list
of servers.
--onall
Run all the jobs on all computers given with --sshlogin. GNU
parallel will log into --jobs number of computers in parallel and
run one job at a time on the computer. The order of the jobs will
not be changed, but some computers may finish before others.
When using --group the output will be grouped by each server, so
all the output from one server will be grouped together.
--joblog will contain an entry for each job on each server, so
there will be several job sequence 1.
--output-as-files
--outputasfiles
--files
Instead of printing the output to stdout (standard output) the
output of each job is saved in a file and the filename is then
printed.
See also: --results
--pipe
--spreadstdin
Spread input to jobs on stdin (standard input). Read a block of
data from stdin (standard input) and give one block of data as
input to one job.
The block size is determined by --block. The strings --recstart and
--recend tell GNU parallel how a record starts and/or ends. The
block read will have the final partial record removed before the
block is passed on to the job. The partial record will be prepended
to next block.
If --recstart is given this will be used to split at record start.
If --recend is given this will be used to split at record end.
If both --recstart and --recend are given both will have to match
to find a split position.
If neither --recstart nor --recend are given --recend defaults to
'\n'. To have no record separator use --recend "".
--files is often used with --pipe.
--pipe maxes out at around 1 GB/s input, and 100 MB/s output. If
performance is important use --pipepart.
See also: --recstart, --recend, --fifo, --cat, --pipepart, --files.
--pipepart
Pipe parts of a physical file. --pipepart works similar to --pipe,
but is much faster.
--pipepart has a few limitations:
o The file must be a normal file or a block device (technically it
must be seekable) and must be given using -a or ::::. The file
cannot be a pipe, a fifo, or a stream as they are not seekable.
If using a block device with lot of NUL bytes, remember to set
--recend ''.
o Record counting (-N) and line counting (-L/-l) do not work.
Instead use --recstart and --recend to determine where records
end.
--plain
Ignore any --profile, $PARALLEL, and ~/.parallel/config to get full
control on the command line (used by GNU parallel internally when
called with --sshlogin).
--plus
Activate additional replacement strings: {+/} {+.} {+..} {+...}
{..} {...} {/..} {/...} {##}. The idea being that '{+foo}' matches
the opposite of '{foo}' and {} = {+/}/{/} = {.}.{+.} =
{+/}/{/.}.{+.} = {..}.{+..} = {+/}/{/..}.{+..} = {...}.{+...} =
{+/}/{/...}.{+...}
{##} is the total number of jobs to be run. It is incompatible with
-X/-m/--xargs.
{0%} zero-padded jobslot.
{0#} zero-padded sequence number.
{choose_k} is inspired by n choose k: Given a list of n elements,
choose k. k is the number of input sources and n is the number of
arguments in an input source. The content of the input sources
must be the same and the arguments must be unique.
Shorthands for variables:
{slot} $PARALLEL_JOBSLOT (see {%})
{sshlogin} $PARALLEL_SSHLOGIN
{host} $PARALLEL_SSHHOST
{agrp} $PARALLEL_ARGHOSTGROUPS
{hgrp} $PARALLEL_HOSTGROUPS
The following dynamic replacement strings are also activated. They
are inspired by bash's parameter expansion:
{:-str} str if the value is empty
{:num} remove the first num characters
{:num1:num2} characters from num1 to num2
{#regexp} remove prefix regexp (non-greedy)
{##regexp} remove prefix regexp (greedy)
{%regexp} remove postfix regexp (non-greedy)
{%%regexp} remove postfix regexp (greedy)
{/regexp/str} replace regexp with str
{^str} uppercase str if found at the start
{^^str} uppercase str
{,str} lowercase str if found at the start
{,,str} lowercase str
--progress
Show progress of computations. List the computers involved in the
task with number of CPUs detected and the max number of jobs to
run. After that show progress for each computer: number of running
jobs, number of completed jobs, and percentage of all jobs done by
this computer. The percentage will only be available after all jobs
have been scheduled as GNU parallel only read the next job when
ready to schedule it - this is to avoid wasting time and memory by
reading everything at startup.
By sending GNU parallel SIGUSR2 you can toggle turning on/off
--progress on a running GNU parallel process.
See also: --eta and --bar.
--max-line-length-allowed
Print the maximal number of characters allowed on the command line
and exit (used by GNU parallel itself to determine the line length
on remote computers).
--number-of-cpus (obsolete)
Print the number of physical CPU cores and exit.
--number-of-cores
Print the number of physical CPU cores and exit (used by GNU
parallel itself to determine the number of physical CPU cores on
remote computers).
--number-of-sockets
Print the number of filled CPU sockets and exit (used by GNU
parallel itself to determine the number of filled CPU sockets on
remote computers).
--number-of-threads
Print the number of hyperthreaded CPU cores and exit (used by GNU
parallel itself to determine the number of hyperthreaded CPU cores
on remote computers).
--no-keep-order
Overrides an earlier --keep-order (e.g. if set in
~/.parallel/config).
--nice niceness
Run the command at this niceness.
By default GNU parallel will run jobs at the same nice level as GNU
parallel is started - both on the local machine and remote servers,
so you are unlikely to ever use this option.
Setting --nice will override this nice level. If the nice level is
smaller than the current nice level, it will only affect remote
jobs (e.g. if current level is 10 then --nice 5 will cause local
jobs to be run at level 10, but remote jobs run at nice level 5).
--interactive
-p Prompt the user about whether to run each command line and read a
line from the terminal. Only run the command line if the response
starts with 'y' or 'Y'. Implies -t.
--parens parensstring
Define start and end parenthesis for {= perl expression =}. The
left and the right parenthesis can be multiple characters and are
assumed to be the same length. The default is {==} giving {= as the
start parenthesis and =} as the end parenthesis.
Another useful setting is ,,,, which would make both parenthesis
,,:
parallel --parens ,,,, echo foo is ,,s/I/O/g,, ::: FII
See also: --rpl {= perl expression =}
--profile profilename
-J profilename
Use profile profilename for options. This is useful if you want to
have multiple profiles. You could have one profile for running jobs
in parallel on the local computer and a different profile for
running jobs on remote computers. See the section PROFILE FILES for
examples.
profilename corresponds to the file ~/.parallel/profilename.
You can give multiple profiles by repeating --profile. If parts of
the profiles conflict, the later ones will be used.
Default: config
--quote
-q Quote command. If your command contains special characters that
should not be interpreted by the shell (e.g. ; \ | *), use --quote
to escape these. The command must be a simple command (see man
bash) without redirections and without variable assignments.
See the section QUOTING. Most people will not need this. Quoting
is disabled by default.
--no-run-if-empty
-r If the stdin (standard input) only contains whitespace, do not run
the command.
If used with --pipe this is slow.
--noswap
Do not start new jobs on a given computer if there is both swap-in
and swap-out activity.
The swap activity is only sampled every 10 seconds as the sampling
takes 1 second to do.
Swap activity is computed as (swap-in)*(swap-out) which in practice
is a good value: swapping out is not a problem, swapping in is not
a problem, but both swapping in and out usually indicates a
problem.
--memfree and --memsuspend may give better results, so try using
those first.
--record-env
Record current environment variables in ~/.parallel/ignored_vars.
This is useful before using --env _.
See also: --env, --session.
--recstart startstring
--recend endstring
If --recstart is given startstring will be used to split at record
start.
If --recend is given endstring will be used to split at record end.
If both --recstart and --recend are given the combined string
endstringstartstring will have to match to find a split position.
This is useful if either startstring or endstring match in the
middle of a record.
If neither --recstart nor --recend are given then --recend defaults
to '\n'. To have no record separator use --recend "".
--recstart and --recend are used with --pipe.
Use --regexp to interpret --recstart and --recend as regular
expressions. This is slow, however.
--regexp
Use --regexp to interpret --recstart and --recend as regular
expressions. This is slow, however.
--remove-rec-sep
--removerecsep
--rrs
Remove the text matched by --recstart and --recend before piping it
to the command.
Only used with --pipe.
--results name
--res name
Save the output into files.
Simple string output dir
If name does not contain replacement strings and does not end in
.csv/.tsv, the output will be stored in a directory tree rooted at
name. Within this directory tree, each command will result in
three files: name/<ARGS>/stdout and name/<ARGS>/stderr,
name/<ARGS>/seq, where <ARGS> is a sequence of directories
representing the header of the input source (if using --header :)
or the number of the input source and corresponding values.
E.g:
parallel --header : --results foo echo {a} {b} \
::: a I II ::: b III IIII
will generate the files:
foo/a/II/b/III/seq
foo/a/II/b/III/stderr
foo/a/II/b/III/stdout
foo/a/II/b/IIII/seq
foo/a/II/b/IIII/stderr
foo/a/II/b/IIII/stdout
foo/a/I/b/III/seq
foo/a/I/b/III/stderr
foo/a/I/b/III/stdout
foo/a/I/b/IIII/seq
foo/a/I/b/IIII/stderr
foo/a/I/b/IIII/stdout
and
parallel --results foo echo {1} {2} ::: I II ::: III IIII
will generate the files:
foo/1/II/2/III/seq
foo/1/II/2/III/stderr
foo/1/II/2/III/stdout
foo/1/II/2/IIII/seq
foo/1/II/2/IIII/stderr
foo/1/II/2/IIII/stdout
foo/1/I/2/III/seq
foo/1/I/2/III/stderr
foo/1/I/2/III/stdout
foo/1/I/2/IIII/seq
foo/1/I/2/IIII/stderr
foo/1/I/2/IIII/stdout
CSV file output
If name ends in .csv/.tsv the output will be a CSV-file named name.
.csv gives a comma separated value file. .tsv gives a TAB separated
value file.
-.csv/-.tsv are special: It will give the file on stdout (standard
output).
JSON file output
If name ends in .json the output will be a JSON-file named name.
-.json is special: It will give the file on stdout (standard
output).
Replacement string output file
If name contains a replacement string and the replaced result does
not end in /, then the standard output will be stored in a file
named by this result. Standard error will be stored in the same
file name with '.err' added, and the sequence number will be stored
in the same file name with '.seq' added.
E.g.
parallel --results my_{} echo ::: foo bar baz
will generate the files:
my_bar
my_bar.err
my_bar.seq
my_baz
my_baz.err
my_baz.seq
my_foo
my_foo.err
my_foo.seq
Replacement string output dir
If name contains a replacement string and the replaced result ends
in /, then output files will be stored in the resulting dir.
E.g.
parallel --results my_{}/ echo ::: foo bar baz
will generate the files:
my_bar/seq
my_bar/stderr
my_bar/stdout
my_baz/seq
my_baz/stderr
my_baz/stdout
my_foo/seq
my_foo/stderr
my_foo/stdout
See also: --files, --tag, --header, --joblog.
--resume
Resumes from the last unfinished job. By reading --joblog or the
--results dir GNU parallel will figure out the last unfinished job
and continue from there. As GNU parallel only looks at the sequence
numbers in --joblog then the input, the command, and --joblog all
have to remain unchanged; otherwise GNU parallel may run wrong
commands.
See also: --joblog, --results, --resume-failed, --retries.
--resume-failed
Retry all failed and resume from the last unfinished job. By
reading --joblog GNU parallel will figure out the failed jobs and
run those again. After that it will resume last unfinished job and
continue from there. As GNU parallel only looks at the sequence
numbers in --joblog then the input, the command, and --joblog all
have to remain unchanged; otherwise GNU parallel may run wrong
commands.
See also: --joblog, --resume, --retry-failed, --retries.
--retry-failed
Retry all failed jobs in joblog. By reading --joblog GNU parallel
will figure out the failed jobs and run those again.
--retry-failed ignores the command and arguments on the command
line: It only looks at the joblog.
Differences between --resume, --resume-failed, --retry-failed
In this example exit {= $_%=2 =} will cause every other job to
fail.
timeout -k 1 4 parallel --joblog log -j10 \
'sleep {}; exit {= $_%=2 =}' ::: {10..1}
4 jobs completed. 2 failed:
Seq [...] Exitval Signal Command
10 [...] 1 0 sleep 1; exit 1
9 [...] 0 0 sleep 2; exit 0
8 [...] 1 0 sleep 3; exit 1
7 [...] 0 0 sleep 4; exit 0
--resume does not care about the Exitval, but only looks at Seq. If
the Seq is run, it will not be run again. So if needed, you can
change the command for the seqs not run yet:
parallel --resume --joblog log -j10 \
'sleep .{}; exit {= $_%=2 =}' ::: {10..1}
Seq [...] Exitval Signal Command
[... as above ...]
1 [...] 0 0 sleep .10; exit 0
6 [...] 1 0 sleep .5; exit 1
5 [...] 0 0 sleep .6; exit 0
4 [...] 1 0 sleep .7; exit 1
3 [...] 0 0 sleep .8; exit 0
2 [...] 1 0 sleep .9; exit 1
--resume-failed cares about the Exitval, but also only looks at Seq
to figure out which commands to run. Again this means you can
change the command, but not the arguments. It will run the failed
seqs and the seqs not yet run:
parallel --resume-failed --joblog log -j10 \
'echo {};sleep .{}; exit {= $_%=3 =}' ::: {10..1}
Seq [...] Exitval Signal Command
[... as above ...]
10 [...] 1 0 echo 1;sleep .1; exit 1
8 [...] 0 0 echo 3;sleep .3; exit 0
6 [...] 2 0 echo 5;sleep .5; exit 2
4 [...] 1 0 echo 7;sleep .7; exit 1
2 [...] 0 0 echo 9;sleep .9; exit 0
--retry-failed cares about the Exitval, but takes the command from
the joblog. It ignores any arguments or commands given on the
command line:
parallel --retry-failed --joblog log -j10 this part is ignored
Seq [...] Exitval Signal Command
[... as above ...]
10 [...] 1 0 echo 1;sleep .1; exit 1
6 [...] 2 0 echo 5;sleep .5; exit 2
4 [...] 1 0 echo 7;sleep .7; exit 1
See also: --joblog, --resume, --resume-failed, --retries.
--retries n
If a job fails, retry it on another computer on which it has not
failed. Do this n times. If there are fewer than n computers in
--sshlogin GNU parallel will re-use all the computers. This is
useful if some jobs fail for no apparent reason (such as network
failure).
--return filename
Transfer files from remote computers. --return is used with
--sshlogin when the arguments are files on the remote computers.
When processing is done the file filename will be transferred from
the remote computer using rsync and will be put relative to the
default login dir. E.g.
echo foo/bar.txt | parallel --return {.}.out \
--sshlogin server.example.com touch {.}.out
This will transfer the file $HOME/foo/bar.out from the computer
server.example.com to the file foo/bar.out after running touch
foo/bar.out on server.example.com.
parallel -S server --trc out/./{}.out touch {}.out ::: in/file
This will transfer the file in/file.out from the computer
server.example.com to the files out/in/file.out after running touch
in/file.out on server.
echo /tmp/foo/bar.txt | parallel --return {.}.out \
--sshlogin server.example.com touch {.}.out
This will transfer the file /tmp/foo/bar.out from the computer
server.example.com to the file /tmp/foo/bar.out after running touch
/tmp/foo/bar.out on server.example.com.
Multiple files can be transferred by repeating the option multiple
times:
echo /tmp/foo/bar.txt | parallel \
--sshlogin server.example.com \
--return {.}.out --return {.}.out2 touch {.}.out {.}.out2
--return is often used with --transferfile and --cleanup.
--return is ignored when used with --sshlogin : or when not used
with --sshlogin.
For details on transferring see --transferfile.
--round-robin
--round
Normally --pipe will give a single block to each instance of the
command. With --roundrobin all blocks will at random be written to
commands already running. This is useful if the command takes a
long time to initialize.
--keep-order will not work with --roundrobin as it is impossible to
track which input block corresponds to which output.
--roundrobin implies --pipe, except if --pipepart is given.
See also: --group-by, --shard.
--rpl 'tag perl expression'
Use tag as a replacement string for perl expression. This makes it
possible to define your own replacement strings. GNU parallel's 7
replacement strings are implemented as:
--rpl '{} '
--rpl '{#} 1 $_=$job->seq()'
--rpl '{%} 1 $_=$job->slot()'
--rpl '{/} s:.*/::'
--rpl '{//} $Global::use{"File::Basename"} ||=
eval "use File::Basename; 1;"; $_ = dirname($_);'
--rpl '{/.} s:.*/::; s:\.[^/.]+$::;'
--rpl '{.} s:\.[^/.]+$::'
The --plus replacement strings are implemented as:
--rpl '{+/} s:/[^/]*$::'
--rpl '{+.} s:.*\.::'
--rpl '{+..} s:.*\.([^.]*\.):$1:'
--rpl '{+...} s:.*\.([^.]*\.[^.]*\.):$1:'
--rpl '{..} s:\.[^/.]+$::; s:\.[^/.]+$::'
--rpl '{...} s:\.[^/.]+$::; s:\.[^/.]+$::; s:\.[^/.]+$::'
--rpl '{/..} s:.*/::; s:\.[^/.]+$::; s:\.[^/.]+$::'
--rpl '{/...} s:.*/::;s:\.[^/.]+$::;s:\.[^/.]+$::;s:\.[^/.]+$::'
--rpl '{##} $_=total_jobs()'
--rpl '{:-(.+?)} $_ ||= $$1'
--rpl '{:(\d+?)} substr($_,0,$$1) = ""'
--rpl '{:(\d+?):(\d+?)} $_ = substr($_,$$1,$$2);'
--rpl '{#([^#].*?)} s/^$$1//;'
--rpl '{%(.+?)} s/$$1$//;'
--rpl '{/(.+?)/(.*?)} s/$$1/$$2/;'
--rpl '{^(.+?)} s/^($$1)/uc($1)/e;'
--rpl '{^^(.+?)} s/($$1)/uc($1)/eg;'
--rpl '{,(.+?)} s/^($$1)/lc($1)/e;'
--rpl '{,,(.+?)} s/($$1)/lc($1)/eg;'
If the user defined replacement string starts with '{' it can also
be used as a positional replacement string (like {2.}).
It is recommended to only change $_ but you have full access to all
of GNU parallel's internal functions and data structures.
Here are a few examples:
Is the job sequence even or odd?
--rpl '{odd} $_ = seq() % 2 ? "odd" : "even"'
Pad job sequence with leading zeros to get equal width
--rpl '{0#} $f=1+int("".(log(total_jobs())/log(10)));
$_=sprintf("%0${f}d",seq())'
Job sequence counting from 0
--rpl '{#0} $_ = seq() - 1'
Job slot counting from 2
--rpl '{%1} $_ = slot() + 1'
Remove all extensions
--rpl '{:} s:(\.[^/]+)*$::'
You can have dynamic replacement strings by including parenthesis
in the replacement string and adding a regular expression between
the parenthesis. The matching string will be inserted as $$1:
parallel --rpl '{%(.*?)} s/$$1//' echo {%.tar.gz} ::: my.tar.gz
parallel --rpl '{:%(.+?)} s:$$1(\.[^/]+)*$::' \
echo {:%_file} ::: my_file.tar.gz
parallel -n3 --rpl '{/:%(.*?)} s:.*/(.*)$$1(\.[^/]+)*$:$1:' \
echo job {#}: {2} {2.} {3/:%_1} ::: a/b.c c/d.e f/g_1.h.i
You can even use multiple matches:
parallel --rpl '{/(.+?)/(.*?)} s/$$1/$$2/;'
echo {/replacethis/withthis} {/b/C} ::: a_replacethis_b
parallel --rpl '{(.*?)/(.*?)} $_="$$2$_$$1"' \
echo {swap/these} ::: -middle-
See also: {= perl expression =} --parens
--rsync-opts options
Options to pass on to rsync. Setting --rsync-opts takes precedence
over setting the environment variable $PARALLEL_RSYNC_OPTS.
--max-chars=max-chars
-s max-chars
Use at most max-chars characters per command line, including the
command and initial-arguments and the terminating nulls at the ends
of the argument strings. The largest allowed value is system-
dependent, and is calculated as the argument length limit for exec,
less the size of your environment. The default value is the
maximum.
max-chars can be postfixed with K, M, G, T, P, k, m, g, t, or p
(see UNIT PREFIX).
Implies -X unless -m is set.
--show-limits
Display the limits on the command-line length which are imposed by
the operating system and the -s option. Pipe the input from
/dev/null (and perhaps specify --no-run-if-empty) if you don't want
GNU parallel to do anything.
--semaphore
Work as a counting semaphore. --semaphore will cause GNU parallel
to start command in the background. When the number of jobs given
by --jobs is reached, GNU parallel will wait for one of these to
complete before starting another command.
--semaphore implies --bg unless --fg is specified.
--semaphore implies --semaphorename `tty` unless --semaphorename is
specified.
Used with --fg, --wait, and --semaphorename.
The command sem is an alias for parallel --semaphore.
See also: man sem.
--semaphorename name
--id name
Use name as the name of the semaphore. Default is the name of the
controlling tty (output from tty).
The default normally works as expected when used interactively, but
when used in a script name should be set. $$ or my_task_name are
often a good value.
The semaphore is stored in ~/.parallel/semaphores/
Implies --semaphore.
See also: man sem.
--semaphoretimeout secs
--st secs
If secs > 0: If the semaphore is not released within secs seconds,
take it anyway.
If secs < 0: If the semaphore is not released within secs seconds,
exit.
Implies --semaphore.
See also: man sem.
--seqreplace replace-str
Use the replacement string replace-str instead of {#} for job
sequence number.
--session
Record names in current environment in $PARALLEL_IGNORED_NAMES and
exit. Only used with env_parallel. Aliases, functions, and
variables with names in $PARALLEL_IGNORED_NAMES will not be copied.
Only supported in Ash, Bash, Dash, Ksh, Sh, and Zsh.
See also: --env, --record-env.
--shard shardexpr
Use shardexpr as shard key and shard input to the jobs.
shardexpr is [column number|column name] [perlexpression] e.g. 3,
Address, 3 $_%=100, Address s/\d//g.
Each input line is split using --colsep. The value of the column is
put into $_, the perl expression is executed, the resulting value
is hashed so that all lines of a given value is given to the same
job slot.
This is similar to sharding in databases.
The performance is in the order of 100K rows per second. Faster if
the shardcol is small (<10), slower if it is big (>100).
--shard requires --pipe and a fixed numeric value for --jobs.
See also: --bin, --group-by, --roundrobin.
--shebang
--hashbang
GNU parallel can be called as a shebang (#!) command as the first
line of a script. The content of the file will be treated as
inputsource.
Like this:
#!/usr/bin/parallel --shebang -r wget
https://ftpmirror.gnu.org/parallel/parallel-20120822.tar.bz2
https://ftpmirror.gnu.org/parallel/parallel-20130822.tar.bz2
https://ftpmirror.gnu.org/parallel/parallel-20140822.tar.bz2
--shebang must be set as the first option.
On FreeBSD env is needed:
#!/usr/bin/env -S parallel --shebang -r wget
https://ftpmirror.gnu.org/parallel/parallel-20120822.tar.bz2
https://ftpmirror.gnu.org/parallel/parallel-20130822.tar.bz2
https://ftpmirror.gnu.org/parallel/parallel-20140822.tar.bz2
There are many limitations of shebang (#!) depending on your
operating system. See details on
https://www.in-ulm.de/~mascheck/various/shebang/
--shebang-wrap
GNU parallel can parallelize scripts by wrapping the shebang line.
If the program can be run like this:
cat arguments | parallel the_program
then the script can be changed to:
#!/usr/bin/parallel --shebang-wrap /original/parser --options
E.g.
#!/usr/bin/parallel --shebang-wrap /usr/bin/python
If the program can be run like this:
cat data | parallel --pipe the_program
then the script can be changed to:
#!/usr/bin/parallel --shebang-wrap --pipe /orig/parser --opts
E.g.
#!/usr/bin/parallel --shebang-wrap --pipe /usr/bin/perl -w
--shebang-wrap must be set as the first option.
--shellquote
Does not run the command but quotes it. Useful for making quoted
composed commands for GNU parallel.
Multiple --shellquote with quote the string multiple times, so
parallel --shellquote | parallel --shellquote can be written as
parallel --shellquote --shellquote.
--shuf
Shuffle jobs. When having multiple input sources it is hard to
randomize jobs. --shuf will generate all jobs, and shuffle them
before running them. This is useful to get a quick preview of the
results before running the full batch.
--skip-first-line
Do not use the first line of input (used by GNU parallel itself
when called with --shebang).
--sql DBURL (obsolete)
Use --sqlmaster instead.
--sqlmaster DBURL
Submit jobs via SQL server. DBURL must point to a table, which will
contain the same information as --joblog, the values from the input
sources (stored in columns V1 .. Vn), and the output (stored in
columns Stdout and Stderr).
If DBURL is prepended with '+' GNU parallel assumes the table is
already made with the correct columns and appends the jobs to it.
If DBURL is not prepended with '+' the table will be dropped and
created with the correct amount of V-columns unless
--sqlmaster does not run any jobs, but it creates the values for
the jobs to be run. One or more --sqlworker must be run to actually
execute the jobs.
If --wait is set, GNU parallel will wait for the jobs to complete.
The format of a DBURL is:
[sql:]vendor://[[user][:pwd]@][host][:port]/[db]/table
E.g.
sql:mysql://hr:hr@localhost:3306/hrdb/jobs
mysql://scott:tiger@my.example.com/pardb/paralleljobs
sql:oracle://scott:tiger@ora.example.com/xe/parjob
postgresql://scott:tiger@pg.example.com/pgdb/parjob
pg:///parjob
sqlite3:///%2Ftmp%2Fpardb.sqlite/parjob
csv:///%2Ftmp%2Fpardb/parjob
Notice how / in the path of sqlite and CVS must be encoded as %2F.
Except the last / in CSV which must be a /.
It can also be an alias from ~/.sql/aliases:
:myalias mysql:///mydb/paralleljobs
--sqlandworker DBURL
Shorthand for: --sqlmaster DBURL --sqlworker DBURL.
--sqlworker DBURL
Execute jobs via SQL server. Read the input sources variables from
the table pointed to by DBURL. The command on the command line
should be the same as given by --sqlmaster.
If you have more than one --sqlworker jobs may be run more than
once.
If --sqlworker runs on the local machine, the hostname in the SQL
table will not be ':' but instead the hostname of the machine.
--ssh sshcommand
GNU parallel defaults to using ssh for remote access. This can be
overridden with --ssh. It can also be set on a per server basis
(see --sshlogin).
--sshdelay mytime
Delay starting next ssh by mytime. GNU parallel will not start
another ssh for the next mytime.
For details on mytime see --delay.
-S
[@hostgroups/][ncpus/]sshlogin[,[@hostgroups/][ncpus/]sshlogin[,...]]
-S @hostgroup
--sshlogin
[@hostgroups/][ncpus/]sshlogin[,[@hostgroups/][ncpus/]sshlogin[,...]]
--sshlogin @hostgroup
Distribute jobs to remote computers. The jobs will be run on a list
of remote computers.
If hostgroups is given, the sshlogin will be added to that
hostgroup. Multiple hostgroups are separated by '+'. The sshlogin
will always be added to a hostgroup named the same as sshlogin.
If only the @hostgroup is given, only the sshlogins in that
hostgroup will be used. Multiple @hostgroup can be given.
GNU parallel will determine the number of CPUs on the remote
computers and run the number of jobs as specified by -j. If the
number ncpus is given GNU parallel will use this number for number
of CPUs on the host. Normally ncpus will not be needed.
An sshlogin is of the form:
[sshcommand [options]] [username@]hostname
The sshlogin must not require a password (ssh-agent, ssh-copy-id,
and sshpass may help with that).
The sshlogin ':' is special, it means 'no ssh' and will therefore
run on the local computer.
The sshlogin '..' is special, it read sshlogins from
~/.parallel/sshloginfile or $XDG_CONFIG_HOME/parallel/sshloginfile
The sshlogin '-' is special, too, it read sshlogins from stdin
(standard input).
To specify more sshlogins separate the sshlogins by comma, newline
(in the same string), or repeat the options multiple times.
For examples: see --sshloginfile.
The remote host must have GNU parallel installed.
--sshlogin is known to cause problems with -m and -X.
--sshlogin is often used with --transferfile, --return, --cleanup,
and --trc.
--sshloginfile filename
--slf filename
File with sshlogins. The file consists of sshlogins on separate
lines. Empty lines and lines starting with '#' are ignored.
Example:
server.example.com
username@server2.example.com
8/my-8-cpu-server.example.com
2/my_other_username@my-dualcore.example.net
# This server has SSH running on port 2222
ssh -p 2222 server.example.net
4/ssh -p 2222 quadserver.example.net
# Use a different ssh program
myssh -p 2222 -l myusername hexacpu.example.net
# Use a different ssh program with default number of CPUs
//usr/local/bin/myssh -p 2222 -l myusername hexacpu
# Use a different ssh program with 6 CPUs
6//usr/local/bin/myssh -p 2222 -l myusername hexacpu
# Assume 16 CPUs on the local computer
16/:
# Put server1 in hostgroup1
@hostgroup1/server1
# Put myusername@server2 in hostgroup1+hostgroup2
@hostgroup1+hostgroup2/myusername@server2
# Force 4 CPUs and put 'ssh -p 2222 server3' in hostgroup1
@hostgroup1/4/ssh -p 2222 server3
When using a different ssh program the last argument must be the
hostname.
Multiple --sshloginfile are allowed.
GNU parallel will first look for the file in current dir; if that
fails it look for the file in ~/.parallel.
The sshloginfile '..' is special, it read sshlogins from
~/.parallel/sshloginfile
The sshloginfile '.' is special, it read sshlogins from
/etc/parallel/sshloginfile
The sshloginfile '-' is special, too, it read sshlogins from stdin
(standard input).
If the sshloginfile is changed it will be re-read when a job
finishes though at most once per second. This makes it possible to
add and remove hosts while running.
This can be used to have a daemon that updates the sshloginfile to
only contain servers that are up:
cp original.slf tmp2.slf
while [ 1 ] ; do
nice parallel --nonall -j0 -k --slf original.slf \
--tag echo | perl 's/\t$//' > tmp.slf
if diff tmp.slf tmp2.slf; then
mv tmp.slf tmp2.slf
fi
sleep 10
done &
parallel --slf tmp2.slf ...
--slotreplace replace-str
Use the replacement string replace-str instead of {%} for job slot
number.
--silent
Silent. The job to be run will not be printed. This is the
default. Can be reversed with -v.
--template file=repl
--tmpl file=repl
Copy file to repl. All replacement strings in the contents of file
will be replaced. All replacement strings in the name repl will be
replaced.
With --cleanup the new file will be removed when the job is done.
If my.tmpl contains this:
Xval: {x}
Yval: {y}
FixedValue: 9
# x with 2 decimals
DecimalX: {=x $_=sprintf("%.2f",$_) =}
TenX: {=x $_=$_*10 =}
RandomVal: {=1 $_=rand() =}
it can be used like this:
myprog() { echo Using "$@"; cat "$@"; }
export -f myprog
parallel --cleanup --header : --tmpl my.tmpl={#}.t myprog {#}.t \
::: x 1.234 2.345 3.45678 ::: y 1 2 3
--tty
Open terminal tty. If GNU parallel is used for starting a program
that accesses the tty (such as an interactive program) then this
option may be needed. It will default to starting only one job at a
time (i.e. -j1), not buffer the output (i.e. -u), and it will open
a tty for the job.
You can of course override -j1 and -u.
Using --tty unfortunately means that GNU parallel cannot kill the
jobs (with --timeout, --memfree, or --halt). This is due to GNU
parallel giving each child its own process group, which is then
killed. Process groups are dependant on the tty.
--tag
Tag lines with arguments. Each output line will be prepended with
the arguments and TAB (\t). When combined with --onall or --nonall
the lines will be prepended with the sshlogin instead.
--tag is ignored when using -u.
--ctag gives the tag a color.
--tagstring str
Tag lines with a string. Each output line will be prepended with
str and TAB (\t). str can contain replacement strings such as {}.
--tagstring is ignored when using -u, --onall, and --nonall.
--ctagstring gives the tag a color.
--tee
Pipe all data to all jobs. Used with --pipe/--pipepart and :::.
seq 1000 | parallel --pipe --tee -v wc {} ::: -w -l -c
How many numbers in 1..1000 contain 0..9, and how many bytes do
they fill:
seq 1000 | parallel --pipe --tee --tag \
'grep {1} | wc {2}' ::: {0..9} ::: -l -c
How many words contain a..z and how many bytes do they fill?
parallel -a /usr/share/dict/words --pipepart --tee --tag \
'grep {1} | wc {2}' ::: {a..z} ::: -l -c
--termseq sequence
Termination sequence. When a job is killed due to --timeout,
--memfree, --halt, or abnormal termination of GNU parallel,
sequence determines how the job is killed. The default is:
TERM,200,TERM,100,TERM,50,KILL,25
which sends a TERM signal, waits 200 ms, sends another TERM signal,
waits 100 ms, sends another TERM signal, waits 50 ms, sends a KILL
signal, waits 25 ms, and exits. GNU parallel detects if a process
dies before the waiting time is up.
--tmpdir dirname
Directory for temporary files. GNU parallel normally buffers output
into temporary files in /tmp. By setting --tmpdir you can use a
different dir for the files. Setting --tmpdir is equivalent to
setting $TMPDIR.
--tmux (Long beta testing)
Use tmux for output. Start a tmux session and run each job in a
window in that session. No other output will be produced.
--tmuxpane (Long beta testing)
Use tmux for output but put output into panes in the first window.
Useful if you want to monitor the progress of less than 100
concurrent jobs.
--timeout duration
Time out for command. If the command runs for longer than duration
seconds it will get killed as per --termseq.
If duration is followed by a % then the timeout will dynamically be
computed as a percentage of the median average runtime of
successful jobs. Only values > 100% will make sense.
duration is normally in seconds, but can be floats postfixed with
s, m, h, or d which would multiply the float by 1, 60, 3600, or
86400. Thus these are equivalent: --timeout 100000 and --timeout
1d3.5h16.6m4s.
--verbose
-t Print the job to be run on stderr (standard error).
See also: -v, -p.
--transfer
Transfer files to remote computers. Shorthand for: --transferfile
{}.
--transferfile filename
--tf filename
--transferfile is used with --sshlogin to transfer files to the
remote computers. The files will be transferred using rsync and
will be put relative to the work dir (see --workdir).
The filename will normally contain a replacement string.
If the path contains /./ the remaining path will be relative to the
work dir (for details: see rsync). If the work dir is /home/user,
the transferring will be as follows:
/tmp/foo/bar => /tmp/foo/bar
tmp/foo/bar => /home/user/tmp/foo/bar
/tmp/./foo/bar => /home/user/foo/bar
tmp/./foo/bar => /home/user/foo/bar
Examples
This will transfer the file foo/bar.txt to the computer
server.example.com to the file $HOME/foo/bar.txt before running wc
foo/bar.txt on server.example.com:
echo foo/bar.txt | parallel --transferfile {} \
--sshlogin server.example.com wc
This will transfer the file /tmp/foo/bar.txt to the computer
server.example.com to the file /tmp/foo/bar.txt before running wc
/tmp/foo/bar.txt on server.example.com:
echo /tmp/foo/bar.txt | parallel --transferfile {} \
--sshlogin server.example.com wc
This will transfer the file /tmp/foo/bar.txt to the computer
server.example.com to the file foo/bar.txt before running wc
./foo/bar.txt on server.example.com:
echo /tmp/./foo/bar.txt | parallel --transferfile {} \
--sshlogin server.example.com wc {= s:.*/\./:./: =}
--transferfile is often used with --return and --cleanup. A
shorthand for --transferfile {} is --transfer.
--transferfile is ignored when used with --sshlogin : or when not
used with --sshlogin.
--trc filename
Transfer, Return, Cleanup. Shorthand for:
--transferfile {} --return filename --cleanup
--trim <n|l|r|lr|rl>
Trim white space in input.
n No trim. Input is not modified. This is the default.
l Left trim. Remove white space from start of input. E.g. " a bc
" -> "a bc ".
r Right trim. Remove white space from end of input. E.g. " a bc "
-> " a bc".
lr
rl Both trim. Remove white space from both start and end of input.
E.g. " a bc " -> "a bc". This is the default if --colsep is
used.
--ungroup
-u Ungroup output. Output is printed as soon as possible and bypasses
GNU parallel internal processing. This may cause output from
different commands to be mixed thus should only be used if you do
not care about the output. Compare these:
seq 4 | parallel -j0 \
'sleep {};echo -n start{};sleep {};echo {}end'
seq 4 | parallel -u -j0 \
'sleep {};echo -n start{};sleep {};echo {}end'
It also disables --tag. GNU parallel outputs faster with -u.
Compare the speeds of these:
parallel seq ::: 300000000 >/dev/null
parallel -u seq ::: 300000000 >/dev/null
parallel --line-buffer seq ::: 300000000 >/dev/null
Can be reversed with --group.
See also: --line-buffer --group
--extensionreplace replace-str
--er replace-str
Use the replacement string replace-str instead of {.} for input
line without extension.
--use-sockets-instead-of-threads
--use-cores-instead-of-threads
--use-cpus-instead-of-cores (obsolete)
Determine how GNU parallel counts the number of CPUs. GNU parallel
uses this number when the number of jobslots is computed relative
to the number of CPUs (e.g. 100% or +1).
CPUs can be counted in three different ways:
sockets The number of filled CPU sockets (i.e. the number of
physical chips).
cores The number of physical cores (i.e. the number of physical
compute cores).
threads The number of hyperthreaded cores (i.e. the number of
virtual cores - with some of them possibly being
hyperthreaded)
Normally the number of CPUs is computed as the number of CPU
threads. With --use-sockets-instead-of-threads or
--use-cores-instead-of-threads you can force it to be computed as
the number of filled sockets or number of cores instead.
Most users will not need these options.
--use-cpus-instead-of-cores is a (misleading) alias for
--use-sockets-instead-of-threads and is kept for backwards
compatibility.
-v Verbose. Print the job to be run on stdout (standard output). Can
be reversed with --silent. See also -t.
Use -v -v to print the wrapping ssh command when running remotely.
--version
-V Print the version GNU parallel and exit.
--workdir mydir
--wd mydir
Jobs will be run in the dir mydir. The default is the current dir
for the local machine, and the login dir for remote computers.
Files transferred using --transferfile and --return will be
relative to mydir on remote computers.
The special mydir value ... will create working dirs under
~/.parallel/tmp/. If --cleanup is given these dirs will be removed.
The special mydir value . uses the current working dir. If the
current working dir is beneath your home dir, the value . is
treated as the relative path to your home dir. This means that if
your home dir is different on remote computers (e.g. if your login
is different) the relative path will still be relative to your home
dir.
To see the difference try:
parallel -S server pwd ::: ""
parallel --wd . -S server pwd ::: ""
parallel --wd ... -S server pwd ::: ""
mydir can contain GNU parallel's replacement strings.
--wait
Wait for all commands to complete.
Used with --semaphore or --sqlmaster.
See also: man sem.
-X Multiple arguments with context replace. Insert as many arguments
as the command line length permits. If multiple jobs are being run
in parallel: distribute the arguments evenly among the jobs. Use
-j1 to avoid this.
If {} is not used the arguments will be appended to the line. If
{} is used as part of a word (like pic{}.jpg) then the whole word
will be repeated. If {} is used multiple times each {} will be
replaced with the arguments.
Normally -X will do the right thing, whereas -m can give unexpected
results if {} is used as part of a word.
Support for -X with --sshlogin is limited and may fail.
See also: -m.
--exit
-x Exit if the size (see the -s option) is exceeded.
--xargs
Multiple arguments. Insert as many arguments as the command line
length permits.
If {} is not used the arguments will be appended to the line. If
{} is used multiple times each {} will be replaced with all the
arguments.
Support for --xargs with --sshlogin is limited and may fail.
See also -X for context replace. If in doubt use -X as that will
most likely do what is needed.
EXAMPLES
EXAMPLE: Working as xargs -n1. Argument appending
GNU parallel can work similar to xargs -n1.
To compress all html files using gzip run:
find . -name '*.html' | parallel gzip --best
If the file names may contain a newline use -0. Substitute FOO BAR with
FUBAR in all files in this dir and subdirs:
find . -type f -print0 | \
parallel -q0 perl -i -pe 's/FOO BAR/FUBAR/g'
Note -q is needed because of the space in 'FOO BAR'.
EXAMPLE: Simple network scanner
prips can generate IP-addresses from CIDR notation. With GNU parallel
you can build a simple network scanner to see which addresses respond
to ping:
prips 130.229.16.0/20 | \
parallel --timeout 2 -j0 \
'ping -c 1 {} >/dev/null && echo {}' 2>/dev/null
EXAMPLE: Reading arguments from command line
GNU parallel can take the arguments from command line instead of stdin
(standard input). To compress all html files in the current dir using
gzip run:
parallel gzip --best ::: *.html
To convert *.wav to *.mp3 using LAME running one process per CPU run:
parallel lame {} -o {.}.mp3 ::: *.wav
EXAMPLE: Inserting multiple arguments
When moving a lot of files like this: mv *.log destdir you will
sometimes get the error:
bash: /bin/mv: Argument list too long
because there are too many files. You can instead do:
ls | grep -E '\.log$' | parallel mv {} destdir
This will run mv for each file. It can be done faster if mv gets as
many arguments that will fit on the line:
ls | grep -E '\.log$' | parallel -m mv {} destdir
In many shells you can also use printf:
printf '%s\0' *.log | parallel -0 -m mv {} destdir
EXAMPLE: Context replace
To remove the files pict0000.jpg .. pict9999.jpg you could do:
seq -w 0 9999 | parallel rm pict{}.jpg
You could also do:
seq -w 0 9999 | perl -pe 's/(.*)/pict$1.jpg/' | parallel -m rm
The first will run rm 10000 times, while the last will only run rm as
many times needed to keep the command line length short enough to avoid
Argument list too long (it typically runs 1-2 times).
You could also run:
seq -w 0 9999 | parallel -X rm pict{}.jpg
This will also only run rm as many times needed to keep the command
line length short enough.
EXAMPLE: Compute intensive jobs and substitution
If ImageMagick is installed this will generate a thumbnail of a jpg
file:
convert -geometry 120 foo.jpg thumb_foo.jpg
This will run with number-of-cpus jobs in parallel for all jpg files in
a directory:
ls *.jpg | parallel convert -geometry 120 {} thumb_{}
To do it recursively use find:
find . -name '*.jpg' | \
parallel convert -geometry 120 {} {}_thumb.jpg
Notice how the argument has to start with {} as {} will include path
(e.g. running convert -geometry 120 ./foo/bar.jpg thumb_./foo/bar.jpg
would clearly be wrong). The command will generate files like
./foo/bar.jpg_thumb.jpg.
Use {.} to avoid the extra .jpg in the file name. This command will
make files like ./foo/bar_thumb.jpg:
find . -name '*.jpg' | \
parallel convert -geometry 120 {} {.}_thumb.jpg
EXAMPLE: Substitution and redirection
This will generate an uncompressed version of .gz-files next to the
.gz-file:
parallel zcat {} ">"{.} ::: *.gz
Quoting of > is necessary to postpone the redirection. Another solution
is to quote the whole command:
parallel "zcat {} >{.}" ::: *.gz
Other special shell characters (such as * ; $ > < | >> <<) also need
to be put in quotes, as they may otherwise be interpreted by the shell
and not given to GNU parallel.
EXAMPLE: Composed commands
A job can consist of several commands. This will print the number of
files in each directory:
ls | parallel 'echo -n {}" "; ls {}|wc -l'
To put the output in a file called <name>.dir:
ls | parallel '(echo -n {}" "; ls {}|wc -l) >{}.dir'
Even small shell scripts can be run by GNU parallel:
find . | parallel 'a={}; name=${a##*/};' \
'upper=$(echo "$name" | tr "[:lower:]" "[:upper:]");'\
'echo "$name - $upper"'
ls | parallel 'mv {} "$(echo {} | tr "[:upper:]" "[:lower:]")"'
Given a list of URLs, list all URLs that fail to download. Print the
line number and the URL.
cat urlfile | parallel "wget {} 2>/dev/null || grep -n {} urlfile"
Create a mirror directory with the same filenames except all files and
symlinks are empty files.
cp -rs /the/source/dir mirror_dir
find mirror_dir -type l | parallel -m rm {} '&&' touch {}
Find the files in a list that do not exist
cat file_list | parallel 'if [ ! -e {} ] ; then echo {}; fi'
EXAMPLE: Composed command with perl replacement string
You have a bunch of file. You want them sorted into dirs. The dir of
each file should be named the first letter of the file name.
parallel 'mkdir -p {=s/(.).*/$1/=}; mv {} {=s/(.).*/$1/=}' ::: *
EXAMPLE: Composed command with multiple input sources
You have a dir with files named as 24 hours in 5 minute intervals:
00:00, 00:05, 00:10 .. 23:55. You want to find the files missing:
parallel [ -f {1}:{2} ] "||" echo {1}:{2} does not exist \
::: {00..23} ::: {00..55..5}
EXAMPLE: Calling Bash functions
If the composed command is longer than a line, it becomes hard to read.
In Bash you can use functions. Just remember to export -f the function.
doit() {
echo Doing it for $1
sleep 2
echo Done with $1
}
export -f doit
parallel doit ::: 1 2 3
doubleit() {
echo Doing it for $1 $2
sleep 2
echo Done with $1 $2
}
export -f doubleit
parallel doubleit ::: 1 2 3 ::: a b
To do this on remote servers you need to transfer the function using
--env:
parallel --env doit -S server doit ::: 1 2 3
parallel --env doubleit -S server doubleit ::: 1 2 3 ::: a b
If your environment (aliases, variables, and functions) is small you
can copy the full environment without having to export -f anything. See
env_parallel.
EXAMPLE: Function tester
To test a program with different parameters:
tester() {
if (eval "$@") >&/dev/null; then
perl -e 'printf "\033[30;102m[ OK ]\033[0m @ARGV\n"' "$@"
else
perl -e 'printf "\033[30;101m[FAIL]\033[0m @ARGV\n"' "$@"
fi
}
export -f tester
parallel tester my_program ::: arg1 arg2
parallel tester exit ::: 1 0 2 0
If my_program fails a red FAIL will be printed followed by the failing
command; otherwise a green OK will be printed followed by the command.
EXAMPLE: Continously show the latest line of output
It can be useful to monitor the output of running jobs.
This shows the most recent output line until a job finishes. After
which the output of the job is printed in full:
parallel '{} | tee >(cat >&3)' ::: 'command 1' 'command 2' \
3> >(perl -ne '$|=1;chomp;printf"%.'$COLUMNS's\r",$_." "x100')
EXAMPLE: Log rotate
Log rotation renames a logfile to an extension with a higher number:
log.1 becomes log.2, log.2 becomes log.3, and so on. The oldest log is
removed. To avoid overwriting files the process starts backwards from
the high number to the low number. This will keep 10 old versions of
the log:
seq 9 -1 1 | parallel -j1 mv log.{} log.'{= $_++ =}'
mv log log.1
EXAMPLE: Removing file extension when processing files
When processing files removing the file extension using {.} is often
useful.
Create a directory for each zip-file and unzip it in that dir:
parallel 'mkdir {.}; cd {.}; unzip ../{}' ::: *.zip
Recompress all .gz files in current directory using bzip2 running 1 job
per CPU in parallel:
parallel "zcat {} | bzip2 >{.}.bz2 && rm {}" ::: *.gz
Convert all WAV files to MP3 using LAME:
find sounddir -type f -name '*.wav' | parallel lame {} -o {.}.mp3
Put all converted in the same directory:
find sounddir -type f -name '*.wav' | \
parallel lame {} -o mydir/{/.}.mp3
EXAMPLE: Removing strings from the argument
If you have directory with tar.gz files and want these extracted in the
corresponding dir (e.g foo.tar.gz will be extracted in the dir foo) you
can do:
parallel --plus 'mkdir {..}; tar -C {..} -xf {}' ::: *.tar.gz
If you want to remove a different ending, you can use {%string}:
parallel --plus echo {%_demo} ::: mycode_demo keep_demo_here
You can also remove a starting string with {#string}
parallel --plus echo {#demo_} ::: demo_mycode keep_demo_here
To remove a string anywhere you can use regular expressions with
{/regexp/replacement} and leave the replacement empty:
parallel --plus echo {/demo_/} ::: demo_mycode remove_demo_here
EXAMPLE: Download 24 images for each of the past 30 days
Let us assume a website stores images like:
https://www.example.com/path/to/YYYYMMDD_##.jpg
where YYYYMMDD is the date and ## is the number 01-24. This will
download images for the past 30 days:
getit() {
date=$(date -d "today -$1 days" +%Y%m%d)
num=$2
echo wget https://www.example.com/path/to/${date}_${num}.jpg
}
export -f getit
parallel getit ::: $(seq 30) ::: $(seq -w 24)
$(date -d "today -$1 days" +%Y%m%d) will give the dates in YYYYMMDD
with $1 days subtracted.
EXAMPLE: Download world map from NASA
NASA provides tiles to download on earthdata.nasa.gov. Download tiles
for Blue Marble world map and create a 10240x20480 map.
base=https://map1a.vis.earthdata.nasa.gov/wmts-geo/wmts.cgi
service="SERVICE=WMTS&REQUEST=GetTile&VERSION=1.0.0"
layer="LAYER=BlueMarble_ShadedRelief_Bathymetry"
set="STYLE=&TILEMATRIXSET=EPSG4326_500m&TILEMATRIX=5"
tile="TILEROW={1}&TILECOL={2}"
format="FORMAT=image%2Fjpeg"
url="$base?$service&$layer&$set&$tile&$format"
parallel -j0 -q wget "$url" -O {1}_{2}.jpg ::: {0..19} ::: {0..39}
parallel eval convert +append {}_{0..39}.jpg line{}.jpg ::: {0..19}
convert -append line{0..19}.jpg world.jpg
EXAMPLE: Download Apollo-11 images from NASA using jq
Search NASA using their API to get JSON for images related to 'apollo
11' and has 'moon landing' in the description.
The search query returns JSON containing URLs to JSON containing
collections of pictures. One of the pictures in each of these
collection is large.
wget is used to get the JSON for the search query. jq is then used to
extract the URLs of the collections. parallel then calls wget to get
each collection, which is passed to jq to extract the URLs of all
images. grep filters out the large images, and parallel finally uses
wget to fetch the images.
base="https://images-api.nasa.gov/search"
q="q=apollo 11"
description="description=moon landing"
media_type="media_type=image"
wget -O - "$base?$q&$description&$media_type" |
jq -r .collection.items[].href |
parallel wget -O - |
jq -r .[] |
grep large |
parallel wget
EXAMPLE: Download video playlist in parallel
youtube-dl is an excellent tool to download videos. It can, however,
not download videos in parallel. This takes a playlist and downloads 10
videos in parallel.
url='youtu.be/watch?v=0wOf2Fgi3DE&list=UU_cznB5YZZmvAmeq7Y3EriQ'
export url
youtube-dl --flat-playlist "https://$url" |
parallel --tagstring {#} --lb -j10 \
youtube-dl --playlist-start {#} --playlist-end {#} '"https://$url"'
EXAMPLE: Prepend last modified date (ISO8601) to file name
parallel mv {} '{= $a=pQ($_); $b=$_;' \
'$_=qx{date -r "$a" +%FT%T}; chomp; $_="$_ $b" =}' ::: *
{= and =} mark a perl expression. pQ perl-quotes the string. date
+%FT%T is the date in ISO8601 with time.
EXAMPLE: Save output in ISO8601 dirs
Save output from ps aux every second into dirs named
yyyy-mm-ddThh:mm:ss+zz:zz.
seq 1000 | parallel -N0 -j1 --delay 1 \
--results '{= $_=`date -Isec`; chomp=}/' ps aux
EXAMPLE: Digital clock with "blinking" :
The : in a digital clock blinks. To make every other line have a ':'
and the rest a ' ' a perl expression is used to look at the 3rd input
source. If the value modulo 2 is 1: Use ":" otherwise use " ":
parallel -k echo {1}'{=3 $_=$_%2?":":" "=}'{2}{3} \
::: {0..12} ::: {0..5} ::: {0..9}
EXAMPLE: Aggregating content of files
This:
parallel --header : echo x{X}y{Y}z{Z} \> x{X}y{Y}z{Z} \
::: X {1..5} ::: Y {01..10} ::: Z {1..5}
will generate the files x1y01z1 .. x5y10z5. If you want to aggregate
the output grouping on x and z you can do this:
parallel eval 'cat {=s/y01/y*/=} > {=s/y01//=}' ::: *y01*
For all values of x and z it runs commands like:
cat x1y*z1 > x1z1
So you end up with x1z1 .. x5z5 each containing the content of all
values of y.
EXAMPLE: Breadth first parallel web crawler/mirrorer
This script below will crawl and mirror a URL in parallel. It
downloads first pages that are 1 click down, then 2 clicks down, then
3; instead of the normal depth first, where the first link link on each
page is fetched first.
Run like this:
PARALLEL=-j100 ./parallel-crawl http://gatt.org.yeslab.org/
Remove the wget part if you only want a web crawler.
It works by fetching a page from a list of URLs and looking for links
in that page that are within the same starting URL and that have not
already been seen. These links are added to a new queue. When all the
pages from the list is done, the new queue is moved to the list of URLs
and the process is started over until no unseen links are found.
#!/bin/bash
# E.g. http://gatt.org.yeslab.org/
URL=$1
# Stay inside the start dir
BASEURL=$(echo $URL | perl -pe 's:#.*::; s:(//.*/)[^/]*:$1:')
URLLIST=$(mktemp urllist.XXXX)
URLLIST2=$(mktemp urllist.XXXX)
SEEN=$(mktemp seen.XXXX)
# Spider to get the URLs
echo $URL >$URLLIST
cp $URLLIST $SEEN
while [ -s $URLLIST ] ; do
cat $URLLIST |
parallel lynx -listonly -image_links -dump {} \; \
wget -qm -l1 -Q1 {} \; echo Spidered: {} \>\&2 |
perl -ne 's/#.*//; s/\s+\d+.\s(\S+)$/$1/ and
do { $seen{$1}++ or print }' |
grep -F $BASEURL |
grep -v -x -F -f $SEEN | tee -a $SEEN > $URLLIST2
mv $URLLIST2 $URLLIST
done
rm -f $URLLIST $URLLIST2 $SEEN
EXAMPLE: Process files from a tar file while unpacking
If the files to be processed are in a tar file then unpacking one file
and processing it immediately may be faster than first unpacking all
files.
tar xvf foo.tgz | perl -ne 'print $l;$l=$_;END{print $l}' | \
parallel echo
The Perl one-liner is needed to make sure the file is complete before
handing it to GNU parallel.
EXAMPLE: Rewriting a for-loop and a while-read-loop
for-loops like this:
(for x in `cat list` ; do
do_something $x
done) | process_output
and while-read-loops like this:
cat list | (while read x ; do
do_something $x
done) | process_output
can be written like this:
cat list | parallel do_something | process_output
For example: Find which host name in a list has IP address 1.2.3 4:
cat hosts.txt | parallel -P 100 host | grep 1.2.3.4
If the processing requires more steps the for-loop like this:
(for x in `cat list` ; do
no_extension=${x%.*};
do_step1 $x scale $no_extension.jpg
do_step2 <$x $no_extension
done) | process_output
and while-loops like this:
cat list | (while read x ; do
no_extension=${x%.*};
do_step1 $x scale $no_extension.jpg
do_step2 <$x $no_extension
done) | process_output
can be written like this:
cat list | parallel "do_step1 {} scale {.}.jpg ; do_step2 <{} {.}" |\
process_output
If the body of the loop is bigger, it improves readability to use a
function:
(for x in `cat list` ; do
do_something $x
[... 100 lines that do something with $x ...]
done) | process_output
cat list | (while read x ; do
do_something $x
[... 100 lines that do something with $x ...]
done) | process_output
can both be rewritten as:
doit() {
x=$1
do_something $x
[... 100 lines that do something with $x ...]
}
export -f doit
cat list | parallel doit
EXAMPLE: Rewriting nested for-loops
Nested for-loops like this:
(for x in `cat xlist` ; do
for y in `cat ylist` ; do
do_something $x $y
done
done) | process_output
can be written like this:
parallel do_something {1} {2} :::: xlist ylist | process_output
Nested for-loops like this:
(for colour in red green blue ; do
for size in S M L XL XXL ; do
echo $colour $size
done
done) | sort
can be written like this:
parallel echo {1} {2} ::: red green blue ::: S M L XL XXL | sort
EXAMPLE: Finding the lowest difference between files
diff is good for finding differences in text files. diff | wc -l gives
an indication of the size of the difference. To find the differences
between all files in the current dir do:
parallel --tag 'diff {1} {2} | wc -l' ::: * ::: * | sort -nk3
This way it is possible to see if some files are closer to other files.
EXAMPLE: for-loops with column names
When doing multiple nested for-loops it can be easier to keep track of
the loop variable if is is named instead of just having a number. Use
--header : to let the first argument be an named alias for the
positional replacement string:
parallel --header : echo {colour} {size} \
::: colour red green blue ::: size S M L XL XXL
This also works if the input file is a file with columns:
cat addressbook.tsv | \
parallel --colsep '\t' --header : echo {Name} {E-mail address}
EXAMPLE: All combinations in a list
GNU parallel makes all combinations when given two lists.
To make all combinations in a single list with unique values, you
repeat the list and use replacement string {choose_k}:
parallel --plus echo {choose_k} ::: A B C D ::: A B C D
parallel --plus echo 2{2choose_k} 1{1choose_k} ::: A B C D ::: A B C D
{choose_k} works for any number of input sources:
parallel --plus echo {choose_k} ::: A B C D ::: A B C D ::: A B C D
EXAMPLE: From a to b and b to c
Assume you have input like:
aardvark
babble
cab
dab
each
and want to run combinations like:
aardvark babble
babble cab
cab dab
dab each
If the input is in the file in.txt:
parallel echo {1} - {2} ::::+ <(head -n -1 in.txt) <(tail -n +2 in.txt)
If the input is in the array $a here are two solutions:
seq $((${#a[@]}-1)) | \
env_parallel --env a echo '${a[{=$_--=}]} - ${a[{}]}'
parallel echo {1} - {2} ::: "${a[@]::${#a[@]}-1}" :::+ "${a[@]:1}"
EXAMPLE: Count the differences between all files in a dir
Using --results the results are saved in /tmp/diffcount*.
parallel --results /tmp/diffcount "diff -U 0 {1} {2} | \
tail -n +3 |grep -v '^@'|wc -l" ::: * ::: *
To see the difference between file A and file B look at the file
'/tmp/diffcount/1/A/2/B'.
EXAMPLE: Speeding up fast jobs
Starting a job on the local machine takes around 10 ms. This can be a
big overhead if the job takes very few ms to run. Often you can group
small jobs together using -X which will make the overhead less
significant. Compare the speed of these:
seq -w 0 9999 | parallel touch pict{}.jpg
seq -w 0 9999 | parallel -X touch pict{}.jpg
If your program cannot take multiple arguments, then you can use GNU
parallel to spawn multiple GNU parallels:
seq -w 0 9999999 | \
parallel -j10 -q -I,, --pipe parallel -j0 touch pict{}.jpg
If -j0 normally spawns 252 jobs, then the above will try to spawn 2520
jobs. On a normal GNU/Linux system you can spawn 32000 jobs using this
technique with no problems. To raise the 32000 jobs limit raise
/proc/sys/kernel/pid_max to 4194303.
If you do not need GNU parallel to have control over each job (so no
need for --retries or --joblog or similar), then it can be even faster
if you can generate the command lines and pipe those to a shell. So if
you can do this:
mygenerator | sh
Then that can be parallelized like this:
mygenerator | parallel --pipe --block 10M sh
E.g.
mygenerator() {
seq 10000000 | perl -pe 'print "echo This is fast job number "';
}
mygenerator | parallel --pipe --block 10M sh
The overhead is 100000 times smaller namely around 100 nanoseconds per
job.
EXAMPLE: Using shell variables
When using shell variables you need to quote them correctly as they may
otherwise be interpreted by the shell.
Notice the difference between:
ARR=("My brother's 12\" records are worth <\$\$\$>"'!' Foo Bar)
parallel echo ::: ${ARR[@]} # This is probably not what you want
and:
ARR=("My brother's 12\" records are worth <\$\$\$>"'!' Foo Bar)
parallel echo ::: "${ARR[@]}"
When using variables in the actual command that contains special
characters (e.g. space) you can quote them using '"$VAR"' or using "'s
and -q:
VAR="My brother's 12\" records are worth <\$\$\$>"
parallel -q echo "$VAR" ::: '!'
export VAR
parallel echo '"$VAR"' ::: '!'
If $VAR does not contain ' then "'$VAR'" will also work (and does not
need export):
VAR="My 12\" records are worth <\$\$\$>"
parallel echo "'$VAR'" ::: '!'
If you use them in a function you just quote as you normally would do:
VAR="My brother's 12\" records are worth <\$\$\$>"
export VAR
myfunc() { echo "$VAR" "$1"; }
export -f myfunc
parallel myfunc ::: '!'
EXAMPLE: Group output lines
When running jobs that output data, you often do not want the output of
multiple jobs to run together. GNU parallel defaults to grouping the
output of each job, so the output is printed when the job finishes. If
you want full lines to be printed while the job is running you can use
--line-buffer. If you want output to be printed as soon as possible you
can use -u.
Compare the output of:
parallel wget --limit-rate=100k \
https://ftpmirror.gnu.org/parallel/parallel-20{}0822.tar.bz2 \
::: {12..16}
parallel --line-buffer wget --limit-rate=100k \
https://ftpmirror.gnu.org/parallel/parallel-20{}0822.tar.bz2 \
::: {12..16}
parallel -u wget --limit-rate=100k \
https://ftpmirror.gnu.org/parallel/parallel-20{}0822.tar.bz2 \
::: {12..16}
EXAMPLE: Tag output lines
GNU parallel groups the output lines, but it can be hard to see where
the different jobs begin. --tag prepends the argument to make that more
visible:
parallel --tag wget --limit-rate=100k \
https://ftpmirror.gnu.org/parallel/parallel-20{}0822.tar.bz2 \
::: {12..16}
--tag works with --line-buffer but not with -u:
parallel --tag --line-buffer wget --limit-rate=100k \
https://ftpmirror.gnu.org/parallel/parallel-20{}0822.tar.bz2 \
::: {12..16}
Check the uptime of the servers in ~/.parallel/sshloginfile:
parallel --tag -S .. --nonall uptime
EXAMPLE: Colorize output
Give each job a new color. Most terminals support ANSI colors with the
escape code "\033[30;3Xm" where 0 <= X <= 7:
seq 10 | \
parallel --tagstring '\033[30;3{=$_=++$::color%8=}m' seq {}
parallel --rpl '{color} $_="\033[30;3".(++$::color%8)."m"' \
--tagstring {color} seq {} ::: {1..10}
To get rid of the initial \t (which comes from --tagstring):
... | perl -pe 's/\t//'
EXAMPLE: Keep order of output same as order of input
Normally the output of a job will be printed as soon as it completes.
Sometimes you want the order of the output to remain the same as the
order of the input. This is often important, if the output is used as
input for another system. -k will make sure the order of output will be
in the same order as input even if later jobs end before earlier jobs.
Append a string to every line in a text file:
cat textfile | parallel -k echo {} append_string
If you remove -k some of the lines may come out in the wrong order.
Another example is traceroute:
parallel traceroute ::: qubes-os.org debian.org freenetproject.org
will give traceroute of qubes-os.org, debian.org and
freenetproject.org, but it will be sorted according to which job
completed first.
To keep the order the same as input run:
parallel -k traceroute ::: qubes-os.org debian.org freenetproject.org
This will make sure the traceroute to qubes-os.org will be printed
first.
A bit more complex example is downloading a huge file in chunks in
parallel: Some internet connections will deliver more data if you
download files in parallel. For downloading files in parallel see:
"EXAMPLE: Download 10 images for each of the past 30 days". But if you
are downloading a big file you can download the file in chunks in
parallel.
To download byte 10000000-19999999 you can use curl:
curl -r 10000000-19999999 https://example.com/the/big/file >file.part
To download a 1 GB file we need 100 10MB chunks downloaded and combined
in the correct order.
seq 0 99 | parallel -k curl -r \
{}0000000-{}9999999 https://example.com/the/big/file > file
EXAMPLE: Parallel grep
grep -r greps recursively through directories. On multicore CPUs GNU
parallel can often speed this up.
find . -type f | parallel -k -j150% -n 1000 -m grep -H -n STRING {}
This will run 1.5 job per CPU, and give 1000 arguments to grep.
EXAMPLE: Grepping n lines for m regular expressions.
The simplest solution to grep a big file for a lot of regexps is:
grep -f regexps.txt bigfile
Or if the regexps are fixed strings:
grep -F -f regexps.txt bigfile
There are 3 limiting factors: CPU, RAM, and disk I/O.
RAM is easy to measure: If the grep process takes up most of your free
memory (e.g. when running top), then RAM is a limiting factor.
CPU is also easy to measure: If the grep takes >90% CPU in top, then
the CPU is a limiting factor, and parallelization will speed this up.
It is harder to see if disk I/O is the limiting factor, and depending
on the disk system it may be faster or slower to parallelize. The only
way to know for certain is to test and measure.
Limiting factor: RAM
The normal grep -f regexps.txt bigfile works no matter the size of
bigfile, but if regexps.txt is so big it cannot fit into memory, then
you need to split this.
grep -F takes around 100 bytes of RAM and grep takes about 500 bytes of
RAM per 1 byte of regexp. So if regexps.txt is 1% of your RAM, then it
may be too big.
If you can convert your regexps into fixed strings do that. E.g. if the
lines you are looking for in bigfile all looks like:
ID1 foo bar baz Identifier1 quux
fubar ID2 foo bar baz Identifier2
then your regexps.txt can be converted from:
ID1.*Identifier1
ID2.*Identifier2
into:
ID1 foo bar baz Identifier1
ID2 foo bar baz Identifier2
This way you can use grep -F which takes around 80% less memory and is
much faster.
If it still does not fit in memory you can do this:
parallel --pipepart -a regexps.txt --block 1M grep -F -f - -n bigfile | \
sort -un | perl -pe 's/^\d+://'
The 1M should be your free memory divided by the number of CPU threads
and divided by 200 for grep -F and by 1000 for normal grep. On
GNU/Linux you can do:
free=$(awk '/^((Swap)?Cached|MemFree|Buffers):/ { sum += $2 }
END { print sum }' /proc/meminfo)
percpu=$((free / 200 / $(parallel --number-of-threads)))k
parallel --pipepart -a regexps.txt --block $percpu --compress \
grep -F -f - -n bigfile | \
sort -un | perl -pe 's/^\d+://'
If you can live with duplicated lines and wrong order, it is faster to
do:
parallel --pipepart -a regexps.txt --block $percpu --compress \
grep -F -f - bigfile
Limiting factor: CPU
If the CPU is the limiting factor parallelization should be done on the
regexps:
cat regexps.txt | parallel --pipe -L1000 --roundrobin --compress \
grep -f - -n bigfile | \
sort -un | perl -pe 's/^\d+://'
The command will start one grep per CPU and read bigfile one time per
CPU, but as that is done in parallel, all reads except the first will
be cached in RAM. Depending on the size of regexps.txt it may be faster
to use --block 10m instead of -L1000.
Some storage systems perform better when reading multiple chunks in
parallel. This is true for some RAID systems and for some network file
systems. To parallelize the reading of bigfile:
parallel --pipepart --block 100M -a bigfile -k --compress \
grep -f regexps.txt
This will split bigfile into 100MB chunks and run grep on each of these
chunks. To parallelize both reading of bigfile and regexps.txt combine
the two using --cat:
parallel --pipepart --block 100M -a bigfile --cat cat regexps.txt \
\| parallel --pipe -L1000 --roundrobin grep -f - {}
If a line matches multiple regexps, the line may be duplicated.
Bigger problem
If the problem is too big to be solved by this, you are probably ready
for Lucene.
EXAMPLE: Using remote computers
To run commands on a remote computer SSH needs to be set up and you
must be able to login without entering a password (The commands ssh-
copy-id, ssh-agent, and sshpass may help you do that).
If you need to login to a whole cluster, you typically do not want to
accept the host key for every host. You want to accept them the first
time and be warned if they are ever changed. To do that:
# Add the servers to the sshloginfile
(echo servera; echo serverb) > .parallel/my_cluster
# Make sure .ssh/config exist
touch .ssh/config
cp .ssh/config .ssh/config.backup
# Disable StrictHostKeyChecking temporarily
(echo 'Host *'; echo StrictHostKeyChecking no) >> .ssh/config
parallel --slf my_cluster --nonall true
# Remove the disabling of StrictHostKeyChecking
mv .ssh/config.backup .ssh/config
The servers in .parallel/my_cluster are now added in .ssh/known_hosts.
To run echo on server.example.com:
seq 10 | parallel --sshlogin server.example.com echo
To run commands on more than one remote computer run:
seq 10 | parallel --sshlogin s1.example.com,s2.example.net echo
Or:
seq 10 | parallel --sshlogin server.example.com \
--sshlogin server2.example.net echo
If the login username is foo on server2.example.net use:
seq 10 | parallel --sshlogin server.example.com \
--sshlogin foo@server2.example.net echo
If your list of hosts is server1-88.example.net with login foo:
seq 10 | parallel -Sfoo@server{1..88}.example.net echo
To distribute the commands to a list of computers, make a file
mycomputers with all the computers:
server.example.com
foo@server2.example.com
server3.example.com
Then run:
seq 10 | parallel --sshloginfile mycomputers echo
To include the local computer add the special sshlogin ':' to the list:
server.example.com
foo@server2.example.com
server3.example.com
:
GNU parallel will try to determine the number of CPUs on each of the
remote computers, and run one job per CPU - even if the remote
computers do not have the same number of CPUs.
If the number of CPUs on the remote computers is not identified
correctly the number of CPUs can be added in front. Here the computer
has 8 CPUs.
seq 10 | parallel --sshlogin 8/server.example.com echo
EXAMPLE: Transferring of files
To recompress gzipped files with bzip2 using a remote computer run:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com \
--transfer "zcat {} | bzip2 -9 >{.}.bz2"
This will list the .gz-files in the logs directory and all directories
below. Then it will transfer the files to server.example.com to the
corresponding directory in $HOME/logs. On server.example.com the file
will be recompressed using zcat and bzip2 resulting in the
corresponding file with .gz replaced with .bz2.
If you want the resulting bz2-file to be transferred back to the local
computer add --return {.}.bz2:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com \
--transfer --return {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"
After the recompressing is done the .bz2-file is transferred back to
the local computer and put next to the original .gz-file.
If you want to delete the transferred files on the remote computer add
--cleanup. This will remove both the file transferred to the remote
computer and the files transferred from the remote computer:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com \
--transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"
If you want run on several computers add the computers to --sshlogin
either using ',' or multiple --sshlogin:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com,server2.example.com \
--sshlogin server3.example.com \
--transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"
You can add the local computer using --sshlogin :. This will disable
the removing and transferring for the local computer only:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com,server2.example.com \
--sshlogin server3.example.com \
--sshlogin : \
--transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"
Often --transfer, --return and --cleanup are used together. They can be
shortened to --trc:
find logs/ -name '*.gz' | \
parallel --sshlogin server.example.com,server2.example.com \
--sshlogin server3.example.com \
--sshlogin : \
--trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"
With the file mycomputers containing the list of computers it becomes:
find logs/ -name '*.gz' | parallel --sshloginfile mycomputers \
--trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"
If the file ~/.parallel/sshloginfile contains the list of computers the
special short hand -S .. can be used:
find logs/ -name '*.gz' | parallel -S .. \
--trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"
EXAMPLE: Advanced file transfer
Assume you have files in in/*, want them processed on server, and
transferred back into /other/dir:
parallel -S server --trc /other/dir/./{/}.out \
cp {/} {/}.out ::: in/./*
EXAMPLE: Distributing work to local and remote computers
Convert *.mp3 to *.ogg running one process per CPU on local computer
and server2:
parallel --trc {.}.ogg -S server2,: \
'mpg321 -w - {} | oggenc -q0 - -o {.}.ogg' ::: *.mp3
EXAMPLE: Running the same command on remote computers
To run the command uptime on remote computers you can do:
parallel --tag --nonall -S server1,server2 uptime
--nonall reads no arguments. If you have a list of jobs you want to run
on each computer you can do:
parallel --tag --onall -S server1,server2 echo ::: 1 2 3
Remove --tag if you do not want the sshlogin added before the output.
If you have a lot of hosts use '-j0' to access more hosts in parallel.
EXAMPLE: Running 'sudo' on remote computers
Put the password into passwordfile then run:
parallel --ssh 'cat passwordfile | ssh' --nonall \
-S user@server1,user@server2 sudo -S ls -l /root
EXAMPLE: Using remote computers behind NAT wall
If the workers are behind a NAT wall, you need some trickery to get to
them.
If you can ssh to a jumphost, and reach the workers from there, then
the obvious solution would be this, but it does not work:
parallel --ssh 'ssh jumphost ssh' -S host1 echo ::: DOES NOT WORK
It does not work because the command is dequoted by ssh twice where as
GNU parallel only expects it to be dequoted once.
You can use a bash function and have GNU parallel quote the command:
jumpssh() { ssh -A jumphost ssh $(parallel --shellquote ::: "$@"); }
export -f jumpssh
parallel --ssh jumpssh -S host1 echo ::: this works
Or you can instead put this in ~/.ssh/config:
Host host1 host2 host3
ProxyCommand ssh jumphost.domain nc -w 1 %h 22
It requires nc(netcat) to be installed on jumphost. With this you can
simply:
parallel -S host1,host2,host3 echo ::: This does work
No jumphost, but port forwards
If there is no jumphost but each server has port 22 forwarded from the
firewall (e.g. the firewall's port 22001 = port 22 on host1, 22002 =
host2, 22003 = host3) then you can use ~/.ssh/config:
Host host1.v
Port 22001
Host host2.v
Port 22002
Host host3.v
Port 22003
Host *.v
Hostname firewall
And then use host{1..3}.v as normal hosts:
parallel -S host1.v,host2.v,host3.v echo ::: a b c
No jumphost, no port forwards
If ports cannot be forwarded, you need some sort of VPN to traverse the
NAT-wall. TOR is one options for that, as it is very easy to get
working.
You need to install TOR and setup a hidden service. In torrc put:
HiddenServiceDir /var/lib/tor/hidden_service/
HiddenServicePort 22 127.0.0.1:22
Then start TOR: /etc/init.d/tor restart
The TOR hostname is now in /var/lib/tor/hidden_service/hostname and is
something similar to izjafdceobowklhz.onion. Now you simply prepend
torsocks to ssh:
parallel --ssh 'torsocks ssh' -S izjafdceobowklhz.onion \
-S zfcdaeiojoklbwhz.onion,auclucjzobowklhi.onion echo ::: a b c
If not all hosts are accessible through TOR:
parallel -S 'torsocks ssh izjafdceobowklhz.onion,host2,host3' \
echo ::: a b c
See more ssh tricks on
https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts
EXAMPLE: Use outrun instead of ssh
outrun lets you run a command on a remote server. outrun sets up a
connection to access files at the source server, and automatically
transfers files. outrun must be installed on the remote system.
You can use outrun in an sshlogin this way:
parallel -S 'outrun user@server eval' command
EXAMPLE: Slurm cluster
The Slurm Workload Manager is used in many clusters.
Here is a simple example of using GNU parallel to call srun:
#!/bin/bash
#SBATCH --time 00:02:00
#SBATCH --ntasks=4
#SBATCH --job-name GnuParallelDemo
#SBATCH --output gnuparallel.out
module purge
module load gnu_parallel
my_parallel="parallel --delay .2 -j $SLURM_NTASKS"
my_srun="srun --export=all --exclusive -n1 --cpus-per-task=1 --cpu-bind=cores"
$my_parallel "$my_srun" echo This is job {} ::: {1..20}
EXAMPLE: Parallelizing rsync
rsync is a great tool, but sometimes it will not fill up the available
bandwidth. Running multiple rsync in parallel can fix this.
cd src-dir
find . -type f |
parallel -j10 -X rsync -zR -Ha ./{} fooserver:/dest-dir/
Adjust -j10 until you find the optimal number.
rsync -R will create the needed subdirectories, so all files are not
put into a single dir. The ./ is needed so the resulting command looks
similar to:
rsync -zR ././sub/dir/file fooserver:/dest-dir/
The /./ is what rsync -R works on.
If you are unable to push data, but need to pull them and the files are
called digits.png (e.g. 000000.png) you might be able to do:
seq -w 0 99 | parallel rsync -Havessh fooserver:src/*{}.png destdir/
EXAMPLE: Use multiple inputs in one command
Copy files like foo.es.ext to foo.ext:
ls *.es.* | perl -pe 'print; s/\.es//' | parallel -N2 cp {1} {2}
The perl command spits out 2 lines for each input. GNU parallel takes 2
inputs (using -N2) and replaces {1} and {2} with the inputs.
Count in binary:
parallel -k echo ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1
Print the number on the opposing sides of a six sided die:
parallel --link -a <(seq 6) -a <(seq 6 -1 1) echo
parallel --link echo :::: <(seq 6) <(seq 6 -1 1)
Convert files from all subdirs to PNG-files with consecutive numbers
(useful for making input PNG's for ffmpeg):
parallel --link -a <(find . -type f | sort) \
-a <(seq $(find . -type f|wc -l)) convert {1} {2}.png
Alternative version:
find . -type f | sort | parallel convert {} {#}.png
EXAMPLE: Use a table as input
Content of table_file.tsv:
foo<TAB>bar
baz <TAB> quux
To run:
cmd -o bar -i foo
cmd -o quux -i baz
you can run:
parallel -a table_file.tsv --colsep '\t' cmd -o {2} -i {1}
Note: The default for GNU parallel is to remove the spaces around the
columns. To keep the spaces:
parallel -a table_file.tsv --trim n --colsep '\t' cmd -o {2} -i {1}
EXAMPLE: Output to database
GNU parallel can output to a database table and a CSV-file:
dburl=csv:///%2Ftmp%2Fmydir
dbtableurl=$dburl/mytable.csv
parallel --sqlandworker $dbtableurl seq ::: {1..10}
It is rather slow and takes up a lot of CPU time because GNU parallel
parses the whole CSV file for each update.
A better approach is to use an SQLite-base and then convert that to
CSV:
dburl=sqlite3:///%2Ftmp%2Fmy.sqlite
dbtableurl=$dburl/mytable
parallel --sqlandworker $dbtableurl seq ::: {1..10}
sql $dburl '.headers on' '.mode csv' 'SELECT * FROM mytable;'
This takes around a second per job.
If you have access to a real database system, such as PostgreSQL, it is
even faster:
dburl=pg://user:pass@host/mydb
dbtableurl=$dburl/mytable
parallel --sqlandworker $dbtableurl seq ::: {1..10}
sql $dburl \
"COPY (SELECT * FROM mytable) TO stdout DELIMITER ',' CSV HEADER;"
Or MySQL:
dburl=mysql://user:pass@host/mydb
dbtableurl=$dburl/mytable
parallel --sqlandworker $dbtableurl seq ::: {1..10}
sql -p -B $dburl "SELECT * FROM mytable;" > mytable.tsv
perl -pe 's/"/""/g; s/\t/","/g; s/^/"/; s/$/"/;
%s=("\\" => "\\", "t" => "\t", "n" => "\n");
s/\\([\\tn])/$s{$1}/g;' mytable.tsv
EXAMPLE: Output to CSV-file for R
If you have no need for the advanced job distribution control that a
database provides, but you simply want output into a CSV file that you
can read into R or LibreCalc, then you can use --results:
parallel --results my.csv seq ::: 10 20 30
R
> mydf <- read.csv("my.csv");
> print(mydf[2,])
> write(as.character(mydf[2,c("Stdout")]),'')
EXAMPLE: Use XML as input
The show Aflyttet on Radio 24syv publishes an RSS feed with their audio
podcasts on: http://arkiv.radio24syv.dk/audiopodcast/channel/4466232
Using xpath you can extract the URLs for 2019 and download them using
GNU parallel:
wget -O - http://arkiv.radio24syv.dk/audiopodcast/channel/4466232 | \
xpath -e "//pubDate[contains(text(),'2019')]/../enclosure/@url" | \
parallel -u wget '{= s/ url="//; s/"//; =}'
EXAMPLE: Run the same command 10 times
If you want to run the same command with the same arguments 10 times in
parallel you can do:
seq 10 | parallel -n0 my_command my_args
EXAMPLE: Working as cat | sh. Resource inexpensive jobs and evaluation
GNU parallel can work similar to cat | sh.
A resource inexpensive job is a job that takes very little CPU, disk
I/O and network I/O. Ping is an example of a resource inexpensive job.
wget is too - if the webpages are small.
The content of the file jobs_to_run:
ping -c 1 10.0.0.1
wget http://example.com/status.cgi?ip=10.0.0.1
ping -c 1 10.0.0.2
wget http://example.com/status.cgi?ip=10.0.0.2
...
ping -c 1 10.0.0.255
wget http://example.com/status.cgi?ip=10.0.0.255
To run 100 processes simultaneously do:
parallel -j 100 < jobs_to_run
As there is not a command the jobs will be evaluated by the shell.
EXAMPLE: Call program with FASTA sequence
FASTA files have the format:
>Sequence name1
sequence
sequence continued
>Sequence name2
sequence
sequence continued
more sequence
To call myprog with the sequence as argument run:
cat file.fasta |
parallel --pipe -N1 --recstart '>' --rrs \
'read a; echo Name: "$a"; myprog $(tr -d "\n")'
EXAMPLE: Call program with interleaved FASTQ records
FASTQ files have the format:
@M10991:61:000000000-A7EML:1:1101:14011:1001 1:N:0:28
CTCCTAGGTCGGCATGATGGGGGAAGGAGAGCATGGGAAGAAATGAGAGAGTAGCAAGG
+
#8BCCGGGGGFEFECFGGGGGGGGG@;FFGGGEG@FF<EE<@FFC,CEGCCGGFF<FGF
Interleaved FASTQ starts with a line like these:
@HWUSI-EAS100R:6:73:941:1973#0/1
@EAS139:136:FC706VJ:2:2104:15343:197393 1:Y:18:ATCACG
@EAS139:136:FC706VJ:2:2104:15343:197393 1:N:18:1
where '/1' and ' 1:' determines this is read 1.
This will cut big.fq into one chunk per CPU core and pass it on stdin
(standard input) to the program fastq-reader:
parallel --pipepart -a big.fq --block -1 --regexp \
--recend '\n' --recstart '@.*(/1| 1:.*)\n[A-Za-z\n\.~]' \
fastq-reader
EXAMPLE: Processing a big file using more CPUs
To process a big file or some output you can use --pipe to split up the
data into blocks and pipe the blocks into the processing program.
If the program is gzip -9 you can do:
cat bigfile | parallel --pipe --recend '' -k gzip -9 > bigfile.gz
This will split bigfile into blocks of 1 MB and pass that to gzip -9 in
parallel. One gzip will be run per CPU. The output of gzip -9 will be
kept in order and saved to bigfile.gz
gzip works fine if the output is appended, but some processing does not
work like that - for example sorting. For this GNU parallel can put the
output of each command into a file. This will sort a big file in
parallel:
cat bigfile | parallel --pipe --files sort |\
parallel -Xj1 sort -m {} ';' rm {} >bigfile.sort
Here bigfile is split into blocks of around 1MB, each block ending in
'\n' (which is the default for --recend). Each block is passed to sort
and the output from sort is saved into files. These files are passed to
the second parallel that runs sort -m on the files before it removes
the files. The output is saved to bigfile.sort.
GNU parallel's --pipe maxes out at around 100 MB/s because every byte
has to be copied through GNU parallel. But if bigfile is a real
(seekable) file GNU parallel can by-pass the copying and send the parts
directly to the program:
parallel --pipepart --block 100m -a bigfile --files sort |\
parallel -Xj1 sort -m {} ';' rm {} >bigfile.sort
EXAMPLE: Grouping input lines
When processing with --pipe you may have lines grouped by a value. Here
is my.csv:
Transaction Customer Item
1 a 53
2 b 65
3 b 82
4 c 96
5 c 67
6 c 13
7 d 90
8 d 43
9 d 91
10 d 84
11 e 72
12 e 102
13 e 63
14 e 56
15 e 74
Let us assume you want GNU parallel to process each customer. In other
words: You want all the transactions for a single customer to be
treated as a single record.
To do this we preprocess the data with a program that inserts a record
separator before each customer (column 2 = $F[1]). Here we first make a
50 character random string, which we then use as the separator:
sep=`perl -e 'print map { ("a".."z","A".."Z")[rand(52)] } (1..50);'`
cat my.csv | \
perl -ape '$F[1] ne $l and print "'$sep'"; $l = $F[1]' | \
parallel --recend $sep --rrs --pipe -N1 wc
If your program can process multiple customers replace -N1 with a
reasonable --blocksize.
EXAMPLE: Running more than 250 jobs workaround
If you need to run a massive amount of jobs in parallel, then you will
likely hit the filehandle limit which is often around 250 jobs. If you
are super user you can raise the limit in /etc/security/limits.conf but
you can also use this workaround. The filehandle limit is per process.
That means that if you just spawn more GNU parallels then each of them
can run 250 jobs. This will spawn up to 2500 jobs:
cat myinput |\
parallel --pipe -N 50 --roundrobin -j50 parallel -j50 your_prg
This will spawn up to 62500 jobs (use with caution - you need 64 GB RAM
to do this, and you may need to increase /proc/sys/kernel/pid_max):
cat myinput |\
parallel --pipe -N 250 --roundrobin -j250 parallel -j250 your_prg
EXAMPLE: Working as mutex and counting semaphore
The command sem is an alias for parallel --semaphore.
A counting semaphore will allow a given number of jobs to be started in
the background. When the number of jobs are running in the background,
GNU sem will wait for one of these to complete before starting another
command. sem --wait will wait for all jobs to complete.
Run 10 jobs concurrently in the background:
for i in *.log ; do
echo $i
sem -j10 gzip $i ";" echo done
done
sem --wait
A mutex is a counting semaphore allowing only one job to run. This will
edit the file myfile and prepends the file with lines with the numbers
1 to 3.
seq 3 | parallel sem sed -i -e '1i{}' myfile
As myfile can be very big it is important only one process edits the
file at the same time.
Name the semaphore to have multiple different semaphores active at the
same time:
seq 3 | parallel sem --id mymutex sed -i -e '1i{}' myfile
EXAMPLE: Mutex for a script
Assume a script is called from cron or from a web service, but only one
instance can be run at a time. With sem and --shebang-wrap the script
can be made to wait for other instances to finish. Here in bash:
#!/usr/bin/sem --shebang-wrap -u --id $0 --fg /bin/bash
echo This will run
sleep 5
echo exclusively
Here perl:
#!/usr/bin/sem --shebang-wrap -u --id $0 --fg /usr/bin/perl
print "This will run ";
sleep 5;
print "exclusively\n";
Here python:
#!/usr/local/bin/sem --shebang-wrap -u --id $0 --fg /usr/bin/python
import time
print "This will run ";
time.sleep(5)
print "exclusively";
EXAMPLE: Start editor with filenames from stdin (standard input)
You can use GNU parallel to start interactive programs like emacs or
vi:
cat filelist | parallel --tty -X emacs
cat filelist | parallel --tty -X vi
If there are more files than will fit on a single command line, the
editor will be started again with the remaining files.
EXAMPLE: Running sudo
sudo requires a password to run a command as root. It caches the
access, so you only need to enter the password again if you have not
used sudo for a while.
The command:
parallel sudo echo ::: This is a bad idea
is no good, as you would be prompted for the sudo password for each of
the jobs. You can either do:
sudo echo This
parallel sudo echo ::: is a good idea
or:
sudo parallel echo ::: This is a good idea
This way you only have to enter the sudo password once.
EXAMPLE: GNU Parallel as queue system/batch manager
GNU parallel can work as a simple job queue system or batch manager.
The idea is to put the jobs into a file and have GNU parallel read from
that continuously. As GNU parallel will stop at end of file we use tail
to continue reading:
true >jobqueue; tail -n+0 -f jobqueue | parallel
To submit your jobs to the queue:
echo my_command my_arg >> jobqueue
You can of course use -S to distribute the jobs to remote computers:
true >jobqueue; tail -n+0 -f jobqueue | parallel -S ..
Output only will be printed when reading the next input after a job has
finished: So you need to submit a job after the first has finished to
see the output from the first job.
If you keep this running for a long time, jobqueue will grow. A way of
removing the jobs already run is by making GNU parallel stop when it
hits a special value and then restart. To use --eof to make GNU
parallel exit, tail also needs to be forced to exit:
true >jobqueue;
while true; do
tail -n+0 -f jobqueue |
(parallel -E StOpHeRe -S ..; echo GNU Parallel is now done;
perl -e 'while(<>){/StOpHeRe/ and last};print <>' jobqueue > j2;
(seq 1000 >> jobqueue &);
echo Done appending dummy data forcing tail to exit)
echo tail exited;
mv j2 jobqueue
done
In some cases you can run on more CPUs and computers during the night:
# Day time
echo 50% > jobfile
cp day_server_list ~/.parallel/sshloginfile
# Night time
echo 100% > jobfile
cp night_server_list ~/.parallel/sshloginfile
tail -n+0 -f jobqueue | parallel --jobs jobfile -S ..
GNU parallel discovers if jobfile or ~/.parallel/sshloginfile changes.
EXAMPLE: GNU Parallel as dir processor
If you have a dir in which users drop files that needs to be processed
you can do this on GNU/Linux (If you know what inotifywait is called on
other platforms file a bug report):
inotifywait -qmre MOVED_TO -e CLOSE_WRITE --format %w%f my_dir |\
parallel -u echo
This will run the command echo on each file put into my_dir or subdirs
of my_dir.
You can of course use -S to distribute the jobs to remote computers:
inotifywait -qmre MOVED_TO -e CLOSE_WRITE --format %w%f my_dir |\
parallel -S .. -u echo
If the files to be processed are in a tar file then unpacking one file
and processing it immediately may be faster than first unpacking all
files. Set up the dir processor as above and unpack into the dir.
Using GNU parallel as dir processor has the same limitations as using
GNU parallel as queue system/batch manager.
EXAMPLE: Locate the missing package
If you have downloaded source and tried compiling it, you may have
seen:
$ ./configure
[...]
checking for something.h... no
configure: error: "libsomething not found"
Often it is not obvious which package you should install to get that
file. Debian has `apt-file` to search for a file. `tracefile` from
https://gitlab.com/ole.tange/tangetools can tell which files a program
tried to access. In this case we are interested in one of the last
files:
$ tracefile -un ./configure | tail | parallel -j0 apt-file search
SPREADING BLOCKS OF DATA
--round-robin, --pipe-part, --shard, --bin and --group-by are all
specialized versions of --pipe.
In the following n is the number of jobslots given by --jobs. A record
starts with --recstart and ends with --recend. It is typically a full
line. A chunk is a number of full records that is approximately the
size of a block. A block can contain half records, a chunk cannot.
--pipe starts one job per chunk. It reads blocks from stdin (standard
input). It finds a record end near a block border and passes a chunk to
the program.
--pipe-part starts one job per chunk - just like normal --pipe. It
first finds record endings near all block borders in the file and then
starts the jobs. By using --block -1 it will set the block size to 1/n
* size-of-file. Used this way it will start n jobs in total.
--round-robin starts n jobs in total. It reads a block and passes a
chunk to whichever job is ready to read. It does not parse the content
except for identifying where a record ends to make sure it only passes
full records.
--shard starts n jobs in total. It parses each line to read the value
in the given column. Based on this value the line is passed to one of
the n jobs. All lines having this value will be given to the same
jobslot.
--bin works like --shard but the value of the column is the jobslot
number it will be passed to. If the value is bigger than n, then n will
be subtracted from the value until the values is smaller than or equal
to n.
--group-by starts one job per chunk. Record borders are not given by
--recend/--recstart. Instead a record is defined by a number of lines
having the same value in a given column. So the value of a given column
changes at a chunk border. With --pipe every line is parsed, with
--pipe-part only a few lines are parsed to find the chunk border.
--group-by can be combined with --round-robin or --pipe-part.
UNIT PREFIX
Many numerical arguments in GNU parallel can be postfixed with K, M, G,
T, P, k, m, g, t, or p which would multiply the number with 1024,
1048576, 1073741824, 1099511627776, 1125899906842624, 1000, 1000000,
1000000000, 1000000000000, or 1000000000000000, respectively.
You can even give it as a math expression. E.g. 1000000 can be written
as 1M-12*2.024*2k.
QUOTING
GNU parallel is very liberal in quoting. You only need to quote
characters that have special meaning in shell:
( ) $ ` ' " < > ; | \
and depending on context these needs to be quoted, too:
~ & # ! ? space * {
Therefore most people will never need more quoting than putting '\' in
front of the special characters.
Often you can simply put \' around every ':
perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"' file
can be quoted:
parallel perl -ne \''/^\S+\s+\S+$/ and print $ARGV,"\n"'\' ::: file
However, when you want to use a shell variable you need to quote the
$-sign. Here is an example using $PARALLEL_SEQ. This variable is set by
GNU parallel itself, so the evaluation of the $ must be done by the sub
shell started by GNU parallel:
seq 10 | parallel -N2 echo seq:\$PARALLEL_SEQ arg1:{1} arg2:{2}
If the variable is set before GNU parallel starts you can do this:
VAR=this_is_set_before_starting
echo test | parallel echo {} $VAR
Prints: test this_is_set_before_starting
It is a little more tricky if the variable contains more than one space
in a row:
VAR="two spaces between each word"
echo test | parallel echo {} \'"$VAR"\'
Prints: test two spaces between each word
If the variable should not be evaluated by the shell starting GNU
parallel but be evaluated by the sub shell started by GNU parallel,
then you need to quote it:
echo test | parallel VAR=this_is_set_after_starting \; echo {} \$VAR
Prints: test this_is_set_after_starting
It is a little more tricky if the variable contains space:
echo test |\
parallel VAR='"two spaces between each word"' echo {} \'"$VAR"\'
Prints: test two spaces between each word
$$ is the shell variable containing the process id of the shell. This
will print the process id of the shell running GNU parallel:
seq 10 | parallel echo $$
And this will print the process ids of the sub shells started by GNU
parallel.
seq 10 | parallel echo \$\$
If the special characters should not be evaluated by the sub shell then
you need to protect it against evaluation from both the shell starting
GNU parallel and the sub shell:
echo test | parallel echo {} \\\$VAR
Prints: test $VAR
GNU parallel can protect against evaluation by the sub shell by using
-q:
echo test | parallel -q echo {} \$VAR
Prints: test $VAR
This is particularly useful if you have lots of quoting. If you want to
run a perl script like this:
perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"' file
It needs to be quoted like one of these:
ls | parallel perl -ne '/^\\S+\\s+\\S+\$/\ and\ print\ \$ARGV,\"\\n\"'
ls | parallel perl -ne \''/^\S+\s+\S+$/ and print $ARGV,"\n"'\'
Notice how spaces, \'s, "'s, and $'s need to be quoted. GNU parallel
can do the quoting by using option -q:
ls | parallel -q perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"'
However, this means you cannot make the sub shell interpret special
characters. For example because of -q this WILL NOT WORK:
ls *.gz | parallel -q "zcat {} >{.}"
ls *.gz | parallel -q "zcat {} | bzip2 >{.}.bz2"
because > and | need to be interpreted by the sub shell.
If you get errors like:
sh: -c: line 0: syntax error near unexpected token
sh: Syntax error: Unterminated quoted string
sh: -c: line 0: unexpected EOF while looking for matching `''
sh: -c: line 1: syntax error: unexpected end of file
zsh:1: no matches found:
then you might try using -q.
If you are using bash process substitution like <(cat foo) then you may
try -q and prepending command with bash -c:
ls | parallel -q bash -c 'wc -c <(echo {})'
Or for substituting output:
ls | parallel -q bash -c \
'tar c {} | tee >(gzip >{}.tar.gz) | bzip2 >{}.tar.bz2'
Conclusion: To avoid dealing with the quoting problems it may be easier
just to write a small script or a function (remember to export -f the
function) and have GNU parallel call that.
LIST RUNNING JOBS
If you want a list of the jobs currently running you can run:
killall -USR1 parallel
GNU parallel will then print the currently running jobs on stderr
(standard error).
COMPLETE RUNNING JOBS BUT DO NOT START NEW JOBS
If you regret starting a lot of jobs you can simply break GNU parallel,
but if you want to make sure you do not have half-completed jobs you
should send the signal SIGHUP to GNU parallel:
killall -HUP parallel
This will tell GNU parallel to not start any new jobs, but wait until
the currently running jobs are finished before exiting.
ENVIRONMENT VARIABLES
$PARALLEL_HOME
Dir where GNU parallel stores config files, semaphores, and
caches information between invocations. Default:
$HOME/.parallel.
$PARALLEL_ARGHOSTGROUPS
When using --hostgroups GNU parallel sets this to the
hostgroups of the job.
Remember to quote the $, so it gets evaluated by the correct
shell. Or use --plus and {agrp}.
$PARALLEL_HOSTGROUPS
When using --hostgroups GNU parallel sets this to the
hostgroups of the sshlogin that the job is run on.
Remember to quote the $, so it gets evaluated by the correct
shell. Or use --plus and {hgrp}.
$PARALLEL_JOBSLOT
Set by GNU parallel and can be used in jobs run by GNU
parallel. Remember to quote the $, so it gets evaluated by
the correct shell. Or use --plus and {slot}.
$PARALLEL_JOBSLOT is the jobslot of the job. It is equal to
{%} unless the job is being retried. See {%} for details.
$PARALLEL_PID
Set by GNU parallel and can be used in jobs run by GNU
parallel. Remember to quote the $, so it gets evaluated by
the correct shell.
This makes it possible for the jobs to communicate directly to
GNU parallel.
Example: If each of the jobs tests a solution and one of jobs
finds the solution the job can tell GNU parallel not to start
more jobs by: kill -HUP $PARALLEL_PID. This only works on the
local computer.
$PARALLEL_RSYNC_OPTS
Options to pass on to rsync. Defaults to: -rlDzR.
$PARALLEL_SHELL
Use this shell for the commands run by GNU parallel:
o $PARALLEL_SHELL. If undefined use:
o The shell that started GNU parallel. If that cannot be
determined:
o $SHELL. If undefined use:
o /bin/sh
$PARALLEL_SSH
GNU parallel defaults to using the ssh command for remote
access. This can be overridden with $PARALLEL_SSH, which again
can be overridden with --ssh. It can also be set on a per
server basis (see --sshlogin).
$PARALLEL_SSHHOST
Set by GNU parallel and can be used in jobs run by GNU
parallel. Remember to quote the $, so it gets evaluated by
the correct shell. Or use --plus and {host}.
$PARALLEL_SSHHOST is the host part of an sshlogin line. E.g.
4//usr/bin/specialssh user@host
becomes:
host
$PARALLEL_SSHLOGIN
Set by GNU parallel and can be used in jobs run by GNU
parallel. Remember to quote the $, so it gets evaluated by
the correct shell. Or use --plus and {sshlogin}.
The value is the sshlogin line with number of cores removed.
E.g.
4//usr/bin/specialssh user@host
becomes:
/usr/bin/specialssh user@host
$PARALLEL_SEQ
Set by GNU parallel and can be used in jobs run by GNU
parallel. Remember to quote the $, so it gets evaluated by
the correct shell.
$PARALLEL_SEQ is the sequence number of the job running.
Example:
seq 10 | parallel -N2 \
echo seq:'$'PARALLEL_SEQ arg1:{1} arg2:{2}
{#} is a shorthand for $PARALLEL_SEQ.
$PARALLEL_TMUX
Path to tmux. If unset the tmux in $PATH is used.
$TMPDIR Directory for temporary files. See: --tmpdir.
$PARALLEL
The environment variable $PARALLEL will be used as default
options for GNU parallel. If the variable contains special
shell characters (e.g. $, *, or space) then these need to be
to be escaped with \.
Example:
cat list | parallel -j1 -k -v ls
cat list | parallel -j1 -k -v -S"myssh user@server" ls
can be written as:
cat list | PARALLEL="-kvj1" parallel ls
cat list | PARALLEL='-kvj1 -S myssh\ user@server' \
parallel echo
Notice the \ after 'myssh' is needed because 'myssh' and
'user@server' must be one argument.
DEFAULT PROFILE (CONFIG FILE)
The global configuration file /etc/parallel/config, followed by user
configuration file ~/.parallel/config (formerly known as .parallelrc)
will be read in turn if they exist. Lines starting with '#' will be
ignored. The format can follow that of the environment variable
$PARALLEL, but it is often easier to simply put each option on its own
line.
Options on the command line take precedence, followed by the
environment variable $PARALLEL, user configuration file
~/.parallel/config, and finally the global configuration file
/etc/parallel/config.
Note that no file that is read for options, nor the environment
variable $PARALLEL, may contain retired options such as --tollef.
PROFILE FILES
If --profile set, GNU parallel will read the profile from that file
rather than the global or user configuration files. You can have
multiple --profiles.
Profiles are searched for in ~/.parallel. If the name starts with / it
is seen as an absolute path. If the name starts with ./ it is seen as a
relative path from current dir.
Example: Profile for running a command on every sshlogin in
~/.ssh/sshlogins and prepend the output with the sshlogin:
echo --tag -S .. --nonall > ~/.parallel/nonall_profile
parallel -J nonall_profile uptime
Example: Profile for running every command with -j-1 and nice
echo -j-1 nice > ~/.parallel/nice_profile
parallel -J nice_profile bzip2 -9 ::: *
Example: Profile for running a perl script before every command:
echo "perl -e '\$a=\$\$; print \$a,\" \",'\$PARALLEL_SEQ',\" \";';" \
> ~/.parallel/pre_perl
parallel -J pre_perl echo ::: *
Note how the $ and " need to be quoted using \.
Example: Profile for running distributed jobs with nice on the remote
computers:
echo -S .. nice > ~/.parallel/dist
parallel -J dist --trc {.}.bz2 bzip2 -9 ::: *
EXIT STATUS
Exit status depends on --halt-on-error if one of these is used:
success=X, success=Y%, fail=Y%.
0 All jobs ran without error. If success=X is used: X jobs ran
without error. If success=Y% is used: Y% of the jobs ran without
error.
1-100 Some of the jobs failed. The exit status gives the number of
failed jobs. If Y% is used the exit status is the percentage of
jobs that failed.
101 More than 100 jobs failed.
255 Other error.
-1 (In joblog and SQL table)
Killed by Ctrl-C, timeout, not enough memory or similar.
-2 (In joblog and SQL table)
skip() was called in {= =}.
-1000 (In SQL table)
Job is ready to run (set by --sqlmaster).
-1220 (In SQL table)
Job is taken by worker (set by --sqlworker).
If fail=1 is used, the exit status will be the exit status of the
failing job.
DIFFERENCES BETWEEN GNU Parallel AND ALTERNATIVES
See: man parallel_alternatives
BUGS
Quoting of newline
Because of the way newline is quoted this will not work:
echo 1,2,3 | parallel -vkd, "echo 'a{}b'"
However, these will all work:
echo 1,2,3 | parallel -vkd, echo a{}b
echo 1,2,3 | parallel -vkd, "echo 'a'{}'b'"
echo 1,2,3 | parallel -vkd, "echo 'a'"{}"'b'"
Speed
Startup
GNU parallel is slow at starting up - around 250 ms the first time and
150 ms after that.
Job startup
Starting a job on the local machine takes around 10 ms. This can be a
big overhead if the job takes very few ms to run. Often you can group
small jobs together using -X which will make the overhead less
significant. Or you can run multiple GNU parallels as described in
EXAMPLE: Speeding up fast jobs.
SSH
When using multiple computers GNU parallel opens ssh connections to
them to figure out how many connections can be used reliably
simultaneously (Namely SSHD's MaxStartups). This test is done for each
host in serial, so if your --sshloginfile contains many hosts it may be
slow.
If your jobs are short you may see that there are fewer jobs running on
the remote systems than expected. This is due to time spent logging in
and out. -M may help here.
Disk access
A single disk can normally read data faster if it reads one file at a
time instead of reading a lot of files in parallel, as this will avoid
disk seeks. However, newer disk systems with multiple drives can read
faster if reading from multiple files in parallel.
If the jobs are of the form read-all-compute-all-write-all, so
everything is read before anything is written, it may be faster to
force only one disk access at the time:
sem --id diskio cat file | compute | sem --id diskio cat > file
If the jobs are of the form read-compute-write, so writing starts
before all reading is done, it may be faster to force only one reader
and writer at the time:
sem --id read cat file | compute | sem --id write cat > file
If the jobs are of the form read-compute-read-compute, it may be faster
to run more jobs in parallel than the system has CPUs, as some of the
jobs will be stuck waiting for disk access.
--nice limits command length
The current implementation of --nice is too pessimistic in the max
allowed command length. It only uses a little more than half of what it
could. This affects -X and -m. If this becomes a real problem for you,
file a bug-report.
Aliases and functions do not work
If you get:
Can't exec "command": No such file or directory
or:
open3: exec of by command failed
or:
/bin/bash: command: command not found
it may be because command is not known, but it could also be because
command is an alias or a function. If it is a function you need to
export -f the function first or use env_parallel. An alias will only
work if you use env_parallel.
Database with MySQL fails randomly
The --sql* options may fail randomly with MySQL. This problem does not
exist with PostgreSQL.
REPORTING BUGS
Report bugs to <bug-parallel@gnu.org> or
https://savannah.gnu.org/bugs/?func=additem&group=parallel
When you write your report, please keep in mind, that you must give the
reader enough information to be able to run exactly what you run. So
you need to include all data and programs that you use to show the
problem.
See a perfect bug report on
https://lists.gnu.org/archive/html/bug-parallel/2015-01/msg00000.html
Your bug report should always include:
o The error message you get (if any). If the error message is not from
GNU parallel you need to show why you think GNU parallel caused this.
o The complete output of parallel --version. If you are not running the
latest released version (see https://ftp.gnu.org/gnu/parallel/) you
should specify why you believe the problem is not fixed in that
version.
o A minimal, complete, and verifiable example (See description on
https://stackoverflow.com/help/mcve).
It should be a complete example that others can run which shows the
problem including all files needed to run the example. This should
preferably be small and simple, so try to remove as many options as
possible.
A combination of yes, seq, cat, echo, wc, and sleep can reproduce
most errors.
If your example requires large files, see if you can make them with
something like seq 100000000 > bigfile or yes | head -n 1000000000 >
file. If you need multiple columns: paste <(seq 1000) <(seq 1000
1999)
If your example requires remote execution, see if you can use
localhost - maybe using another login.
If you have access to a different system (maybe a VirtualBox on your
own machine), test if your MCVE shows the problem on that system. If
it does not, read below.
o The output of your example. If your problem is not easily reproduced
by others, the output might help them figure out the problem.
o Whether you have watched the intro videos
(https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1), walked
through the tutorial (man parallel_tutorial), and read the EXAMPLE
section in the man page (man parallel - search for EXAMPLE:).
Bug dependent on environment
If you suspect the error is dependent on your environment or
distribution, please see if you can reproduce the error on one of these
VirtualBox images:
https://sourceforge.net/projects/virtualboximage/files/
https://www.osboxes.org/virtualbox-images/
Specifying the name of your distribution is not enough as you may have
installed software that is not in the VirtualBox images.
If you cannot reproduce the error on any of the VirtualBox images
above, see if you can build a VirtualBox image on which you can
reproduce the error. If not you should assume the debugging will be
done through you. That will put more burden on you and it is extra
important you give any information that help. In general the problem
will be fixed faster and with less work for you if you can reproduce
the error on a VirtualBox.
In summary
Your report must include:
o parallel --version
o output + error message
o full example including all files
o VirtualBox image, if you cannot reproduce it on other systems
AUTHOR
When using GNU parallel for a publication please cite:
O. Tange (2011): GNU Parallel - The Command-Line Power Tool, ;login:
The USENIX Magazine, February 2011:42-47.
This helps funding further development; and it won't cost you a cent.
If you pay 10000 EUR you should feel free to use GNU Parallel without
citing.
Copyright (C) 2007-10-18 Ole Tange, http://ole.tange.dk
Copyright (C) 2008-2010 Ole Tange, http://ole.tange.dk
Copyright (C) 2010-2021 Ole Tange, http://ole.tange.dk and Free
Software Foundation, Inc.
Parts of the manual concerning xargs compatibility is inspired by the
manual of xargs from GNU findutils 4.4.2.
LICENSE
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or at your
option any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program. If not, see <https://www.gnu.org/licenses/>.
Documentation license I
Permission is granted to copy, distribute and/or modify this
documentation under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, with no Front-Cover Texts, and
with no Back-Cover Texts. A copy of the license is included in the
file LICENSES/GFDL-1.3-or-later.txt.
Documentation license II
You are free:
to Share to copy, distribute and transmit the work
to Remix to adapt the work
Under the following conditions:
Attribution
You must attribute the work in the manner specified by the
author or licensor (but not in any way that suggests that they
endorse you or your use of the work).
Share Alike
If you alter, transform, or build upon this work, you may
distribute the resulting work only under the same, similar or
a compatible license.
With the understanding that:
Waiver Any of the above conditions can be waived if you get
permission from the copyright holder.
Public Domain
Where the work or any of its elements is in the public domain
under applicable law, that status is in no way affected by the
license.
Other Rights
In no way are any of the following rights affected by the
license:
o Your fair dealing or fair use rights, or other applicable
copyright exceptions and limitations;
o The author's moral rights;
o Rights other persons may have either in the work itself or
in how the work is used, such as publicity or privacy
rights.
Notice For any reuse or distribution, you must make clear to others
the license terms of this work.
A copy of the full license is included in the file as
LICENCES/CC-BY-SA-4.0.txt
DEPENDENCIES
GNU parallel uses Perl, and the Perl modules Getopt::Long, IPC::Open3,
Symbol, IO::File, POSIX, and File::Temp.
For --csv it uses the Perl module Text::CSV.
For remote usage it uses rsync with ssh.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | shell/parallel |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
parallel_tutorial(1), env_parallel(1), parset(1), parsort(1),
parallel_alternatives(1), parallel_design(7), niceload(1), sql(1),
ssh(1), ssh-agent(1), sshpass(1), ssh-copy-id(1), rsync(1)
NOTES
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from
https://ftp.gnu.org/gnu/parallel/parallel-20211122.tar.bz2.
Further information about this software can be found on the open source
community website at https://www.gnu.org/software/parallel.
20211022 2021-10-24 PARALLEL(1)