rsyslogd
(1m)
Name
rsyslogd - reliable and extended syslogd
Synopsis
rsyslogd [ -4 ] [ -6 ] [ -A ] [ -d ] [ -f config file ]
[ -i pid file ] [ -l hostlist ] [ -n ] [ -N level ]
[ -q ] [ -Q ] [ -s domainlist ] [ -u userlevel ] [ -v ] [ -w
] [ -x ]
Description
System Administration Commands RSYSLOGD(1M)
NAME
rsyslogd - reliable and extended syslogd
SYNOPSIS
rsyslogd [ -4 ] [ -6 ] [ -A ] [ -d ] [ -f config file ]
[ -i pid file ] [ -l hostlist ] [ -n ] [ -N level ]
[ -q ] [ -Q ] [ -s domainlist ] [ -u userlevel ] [ -v ] [ -w
] [ -x ]
DESCRIPTION
Rsyslogd is a system utility providing support for message
logging. Support of both internet and unix domain sockets
enables this utility to support both local and remote log-
ging.
To use rsyslog's advanced features, you need to look at the
online documentation, because the man pages only cover basic
aspects of operation. For details and configuration exam-
ples, see man page and the online documentation
rsyslogd(1M) is derived from the sysklogd package which in
turn is derived from the stock BSD sources.
Rsyslogd provides a kind of logging that many modern pro-
grams use. Every logged message contains at least a time
and a hostname field, normally a program name field, too,
but that depends on how trusty the logging program is. The
rsyslog package supports free definition of output formats
via templates. It also supports precise timestamps and writ-
ing directly to databases. If the database option is used,
tools like phpLogCon can be used to view the log data.
While the rsyslogd sources have been heavily modified a cou-
ple of notes are in order. First of all there has been a
systematic attempt to ensure that rsyslogd follows its
default, standard BSD behavior. Of course, some configura-
tion file changes are necessary in order to support the tem-
plate system. However, rsyslogd should be able to use a
standard syslog.conf and act like the original syslogd. How-
ever, an original syslogd will not work correctly with a
rsyslog-enhanced configuration file. At best, it will gener-
ate funny looking file names. The second important concept
to note is that this version of rsyslogd interacts transpar-
ently with the version of syslog found in the standard
libraries. If a binary linked to the standard shared
libraries fails to function correctly we would like an exam-
ple of the anomalous behavior.
The main configuration file /etc/rsyslog.conf or an alterna-
tive file, given with the -f option, is read at startup.
Any lines that begin with the hash mark (``#'') and empty
lines are ignored. If an error occurs during parsing the
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System Administration Commands RSYSLOGD(1M)
error element is ignored. It is tried to parse the rest of
the line.
OPTIONS
Note that in version 3 of have been deprecated and replaced
with -c option controls the backward compatibility
-A When sending UDP messages, there are potentially multi-
ple paths to the target destination. By default, rsys-
logd only sends to the first target it can successfully
send to. If -A is given, messages are sent to all tar-
gets. This may improve reliability, but may also cause
message duplication. This option should be enabled only
if it is fully understood.
-4 Causes rsyslogd to listen to IPv4 addresses only. If
neither -4 nor -6 is given, rsyslogd listens to all
configured addresses of the system.
-6 Causes rsyslogd to listen to IPv6 addresses only. If
neither -4 nor -6 is given, rsyslogd listens to all
configured addresses of the system.
-c version
Selects the desired backward compatibility mode. It
must always be the first option on the command line, as
it influences processing of the other options. To use
the rsyslog v3 native interface, specify -c3. To use
compatibility mode , either do not use -c at all or use
-c<version> where version is the rsyslog version that
it shall be compatible with. Using -c0 tells rsyslog to
be command-line compatible to sysklogd, which is the
default if -c is not given. Please note that rsyslogd
issues warning command line option is not given. This
is to alert you that your are running in compatibility
mode. Compatibility mode interferes with your rsys-
log.conf commands and may cause some undesired side-
effects. It is meant to be used with a plain old rsys-
log.conf - if you use new features, things become
messy. So the best advice is to work through this docu-
ment, convert your options and config file and then use
rsyslog in native mode. In order to aid you in this
process, rsyslog logs every compatibility-mode config
file directive it has generated. So you can simply copy
them from your logfile and paste them to the config.
-d Turns on debug mode. Using this the daemon will not
proceed a fork(2) to set itself in the background, but
opposite to that stay in the foreground and write much
debug information on the current tty. See the DEBUG-
GING section for more information.
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System Administration Commands RSYSLOGD(1M)
-f config file
Specify an alternative configuration file instead of
/etc/rsyslog.conf, which is the default.
-i pid file
Specify an alternative pid file instead of the default
one. This option must be used if multiple instances of
rsyslogd should run on a single machine.
-l hostlist
Specify a hostname that should be logged only with its
simple hostname and not the fqdn. Multiple hosts may
be specified using the colon (``:'') separator.
-n Avoid auto-backgrounding. This is needed especially if
the rsyslogd is started and controlled by init(1M),
which is not the case on Solaris.
-N level
Do a coNfig check. Do NOT run in regular mode, just
check configuration file correctness. This option is
meant to verify a config file. To do so, run rsyslogd
interactively in foreground, specifying -f <config-
file> and -N level. The level argument modifies behav-
iour. Currently, 0 is the same as not specifying the -N
option at all (so this makes limited sense) and 1 actu-
ally activates the code. Later, higher levels will mean
more verbosity (this is a forward-compatibility
option).
-q add hostname if DNS fails during ACL processing
During ACL processing, hostnames are resolved to IP
addresses for performance reasons. If DNS fails during
that process, the hostname is added as wildcard text,
which results in proper, but somewhat slower operation
once DNS is up again.
-Q do not resolve hostnames during ACL processing
Do not resolve hostnames to IP addresses during ACL
processing.
-s domainlist
Specify a domainname that should be stripped off before
logging. Multiple domains may be specified using the
colon (``:'') separator. Please be advised that no
sub-domains may be specified but only entire domains.
For example if -s north.de is specified and the host
logging resolves to satu.infodrom.north.de no domain
would be cut, you will have to specify two domains
like: -s north.de:infodrom.north.de.
-u userlevel
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System Administration Commands RSYSLOGD(1M)
This is a "catch all" option for some very seldomly-
used user settings. The "userlevel" variable selects
multiple things. Add the specific values to get the
combined effect of them. A value of 1 prevents rsys-
logd from parsing hostnames and tags inside messages.
A value of 2 prevents rsyslogd from changing to the
root directory. This is almost never a good idea in
production use. This option was introduced in support
of the internal testbed. To combine these two fea-
tures, use a userlevel of 3 (1+2). Whenever you use an
-u option, make sure you really understand what you do
and why you do it.
-v Print version and exit.
-w Suppress warnings issued when messages are received
from non-authorized machines (those, that are in no
AllowedSender list).
-x Disable DNS for remote messages.
SIGNALS
Rsyslogd reacts to a set of signals. You may easily send a
signal to rsyslogd using the following:
kill -SIGNAL $(cat /var/run/rsyslogd.pid)
Note that -SIGNAL must be replaced with the actual signal
you are trying to send, e.g. with HUP. So it then becomes:
kill -HUP $(cat /var/run/rsyslogd.pid)
HUP This lets rsyslogd perform close all open files. Also,
in v3 a full restart will be done in order to read
changed configuration files. Note that this means a
full rsyslogd restart is done. This has, among others,
the consequence that TCP and other connections are torn
down. Also, if any queues are not running in disk
assisted mode or are not set to persist data on shut-
down, queue data is lost. HUPing rsyslogd is an
extremely expensive operation and should only be done
when actually necessary. Actually, it is a rsyslgod
stop immediately followed by a restart. Future versions
will remove this restart functionality of HUP (it will
go away in v5). So it is advised to use HUP only for
closing files, and a "real restart" (e.g. svcadm
restart svc:/system/system-log:rsyslog) to activate
configuration changes.
TERM , INT , QUIT
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System Administration Commands RSYSLOGD(1M)
Rsyslogd will die.
USR1 Switch debugging on/off. This option can only be used
if rsyslogd is started with the -d debug option.
CHLD Wait for childs if some were born, because of wall'ing
messages.
SECURITY THREATS
There is the potential for the rsyslogd daemon to be used as
a conduit for a denial of service attack. A rogue pro-
gram(mer) could very easily flood the rsyslogd daemon with
syslog messages resulting in the log files consuming all the
remaining space on the filesystem. Activating logging over
the inet domain sockets will of course expose a system to
risks outside of programs or individuals on the local
machine.
There are a number of methods of protecting a machine:
1. Implement kernel firewalling to limit which hosts or
networks have access to the 514/UDP socket.
2. Logging can be directed to an isolated or non-root
filesystem which, if filled, will not impair the
machine.
3. The ext2 filesystem can be used which can be configured
to limit a certain percentage of a filesystem to usage
by root only. NOTE that this will require rsyslogd to
be run as a non-root process. ALSO NOTE that this will
prevent usage of remote logging on the default port
since rsyslogd will be unable to bind to the 514/UDP
socket.
4. Disabling inet domain sockets will limit risk to the
local machine.
Message replay and spoofing
If remote logging is enabled, messages can easily be spoofed
and replayed. As the messages are transmitted in clear-
text, an attacker might use the information obtained from
the packets for malicious things. Also, an attacker might
replay recorded messages or spoof a sender's IP address,
which could lead to a wrong perception of system activity.
These can be prevented by using GSS-API authentication and
encryption. Be sure to think about syslog network security
before enabling it.
DEBUGGING
When debugging is turned on using -d option then rsyslogd
will be very verbose by writing much of what it does on
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System Administration Commands RSYSLOGD(1M)
stdout.
FILES
/etc/rsyslog.conf
Configuration file for rsyslogd. See rsyslog.conf(5)
for exact information.
/dev/log
The Unix domain socket to from where local syslog mes-
sages are read.
/var/run/rsyslogd.pid
The file containing the process id of rsyslogd.
/usr/lib/rsyslog
Default directory for rsyslogd modules.
ENVIRONMENT
RSYSLOG_DEBUG
Controls runtime debug support.It contains an option
string with the following options possible (all are
case insensitive):
LogFuncFlow
Print out the logical flow of functions (entering
and exiting them)
FileTrace
Specifies which files to trace LogFuncFlow. If not
set (the default), a LogFuncFlow trace is provided
for all files. Set to limit it to the files speci-
fied.FileTrace may be specified multiple times,
one file each (e.g. export RSYSLOG_DEBUG="Log-
FuncFlow FileTrace=vm.c FileTrace=expr.c"
PrintFuncDB
Print the content of the debug function database
whenever debug information is printed (e.g. abort
case)!
PrintAllDebugInfoOnExit
Print all debug information immediately before
rsyslogd exits (currently not implemented!)
PrintMutexAction
Print mutex action as it happens. Useful for find-
ing deadlocks and such.
NoLogTimeStamp
Do not prefix log lines with a timestamp (default
is to do that).
NoStdOut
Do not emit debug messages to stdout. If RSYS-
LOG_DEBUGLOG is not set, this means no messages
will be displayed at all.
Help Display a very short list of commands - hopefully
a life saver if you can't access the documenta-
tion...
RSYSLOG_DEBUGLOG
If set, writes (almost) all debug message to the
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System Administration Commands RSYSLOGD(1M)
specified log file in addition to stdout.
RSYSLOG_MODDIR
Provides the default directory in which loadable mod-
ules reside.
Further Information
Please visit http://www.rsyslog.com/doc for additional
information, tutorials and a support forum.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+-----------------------------+-------------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-------------------------------+
|Availability |pkg:/system/rsyslog |
+-----------------------------+-------------------------------+
|Service |svc:/system/system-log:rsyslog |
+-----------------------------+-------------------------------+
Solaris Usage
The rsyslog instance of the system-log service is not
enabled by default. To enable it, first "svcadm disable
svc:/system/system-log:default", then "svcadm enable
svc:/system/system-log:rsyslog". If you wish to enable log
rotation, then add each file referenced in rsyslog.conf(4)
to /etc/logadm.conf.
SEE ALSO
rsyslog.conf(4), logger(1), syslog(3C), services(4)
logadm.conf(4)
COLLABORATORS
rsyslogd is derived from sysklogd sources, which in turn was
taken from the BSD sources. Special thanks to Greg Wettstein
(greg@wind.enjellic.com) and Martin Schulze (joey@linux.de)
for the fine sysklogd package.
Rainer Gerhards
Adiscon GmbH
Grossrinderfeld, Germany
rgerhards@adiscon.com
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