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man pages section 1: User Commands

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Updated: Thursday, March 14, 2019
 
 

crontab(1)

Name

crontab - user crontab file

Synopsis

/usr/bin/crontab [filename]
/usr/bin/crontab -e [username]
/usr/bin/crontab -l [username]
/usr/bin/crontab -r [username]
/usr/xpg4/bin/crontab [filename]
/usr/xpg4/bin/crontab -e [username]
/usr/xpg4/bin/crontab -l [username]
/usr/xpg4/bin/crontab -r [username]
/usr/xpg6/bin/crontab [filename]
/usr/xpg6/bin/crontab -e [username]
/usr/xpg6/bin/crontab -l [username]
/usr/xpg6/bin/crontab -r [username]

Description

The crontab utility manages a user's access with cron (see cron(8)) by copying, creating, listing, and removing crontab files. If invoked without options, crontab copies the specified file, or the standard input if no file is specified, into a directory that holds all users' crontabs.

If crontab is invoked with filename, this overwrites an existing crontab entry for the user that invokes it.

crontab Access Control

Users: Access to crontab is allowed:

  • if the user's name appears in /etc/cron.d/cron.allow.

  • if /etc/cron.d/cron.allow does not exist and the user's name is not in /etc/cron.d/cron.deny.

Users: Access to crontab is denied:

  • if /etc/cron.d/cron.allow exists and the user's name is not in it.

  • if /etc/cron.d/cron.allow does not exist and user's name is in /etc/cron.d/cron.deny.

  • if neither file exists, only a user with the solaris.jobs.user authorization is allowed to submit a job.

  • if Solaris Auditing is enabled, the user's shell is not audited and the user is not the crontab owner. This can occur if the user logs in by way of a program, such as some versions of SSH, which does not set audit parameters.

The rules for allow and deny apply to root only if the allow/deny files exist.

The allow/deny files consist of one user name per line.

crontab Entry Format

A crontab file consists of lines of six fields each. The fields are separated by spaces or tabs. The first five are integer patterns that specify the following:

minute (0−59),
hour (0−23),
day of the month (1−31),
month of the year (1−12),
day of the week (0−6 with 0=Sunday).

Each of these patterns can be either an asterisk (meaning all legal values) or a list of elements separated by commas. An element is either a number or two numbers separated by a minus sign (meaning an inclusive range). Time specified here is interpreted in the currently active timezone. At the top of the crontab file this is the timezone which is set system-wide in /etc/default/init. A user can add a line such as:

TZ=timezone

...and all subsequent entries will be interpreted using that timezone, until a new TZ=timezone line is encountered. The specification of days can be made by two fields (day of the month and day of the week). Both are adhered to if specified as a list of elements. See EXAMPLES.

The sixth field of a line in a crontab file is a string that is executed by the shell at the specified times. A percent character in this field (unless escaped by \ ) is translated to a NEWLINE character.

Only the first line (up to a ` % ' or end of line) of the command field is executed by the shell. Other lines are made available to the command as standard input. Any blank line or line beginning with a ` # ' is a comment and is ignored.

The shell is invoked from your $HOME directory. As with $TZ, both $SHELL and $HOME can be set by having a line such as:

SHELL=/usr/bin/someshell

...or:

HOME=somedirectory

...which will take precedence for all the remaining entries in the crontab or until there is another HOME or SHELL entry. It is invoked with an arg0 of the basename of the $SHELL that is currently in effect. A user who wants to have their .profile or equivalent file executed must explicitly do so in the crontab file. cron supplies a default environment for every shell, defining HOME, LOGNAME, SHELL, TZ, and PATH. The default PATH for user cron jobs is /usr/bin; while root cron jobs default to /usr/sbin:/usr/bin. The default PATH can be set in /etc/default/cron (see cron(8)). The TZ, HOME, and SHELL environment variables are set to match those that are in effect in the crontab file at the time.

If you do not redirect the standard output and standard error of your commands, any generated output or errors are mailed to you.

crontab Environment Variables

The following variables are supported:

HOME

Allows the user to choose and alternative directory for cron to change directory to prior to running the command. For example:

HOME=/var/tmp
SHELL

The name of the shell to use to run subsequent commands. For example:

SHELL=/usr/bin/ksh
TZ

Allows the user to choose the timezone in which the cron entries are run. This effects both the environment of the command that is run and the timing of the entry. For example, to have your entries run using the timezone for Iceland, use:

TZ=Iceland

Each of these variables affects all of the lines that follow it in the crontab file, until it is reset by a subsequent line resetting that variable. Hence, it is possible to have multiple timezones supported within a single crontab file.

The lines that are not setting these environment variables are the same as crontab entries that conform to the UNIX standard and are described elsewhere in this man page.

Setting cron Jobs Across Timezones

The default timezone of the cron daemon sets the system-wide timezone for cron entries. This, in turn, is by set by default system-wide using /etc/default/init.

If some form of daylight savings or summer/winter time is in effect, then jobs scheduled during the switchover period could be executed once, twice, or not at all.

Options

The following options are supported:

–e

Edits a copy of the current user's crontab file, or creates an empty file to edit if crontab does not exist. When editing is complete, the file is installed as the user's crontab file.

The environment variable EDITOR determines which editor is invoked with the –e option. All crontab jobs should be submitted using crontab. Do not add jobs by just editing the crontab file, because cron is not aware of changes made this way.

If all lines in the crontab file are deleted, the old crontab file is restored. The correct way to delete all lines is to remove the crontab file using the –r option.

If username is specified, the specified user's crontab file is edited, rather than the current user's crontab file. This can only be done by root or by a user with the solaris.jobs.admin authorization.

–l

Lists the crontab file for the invoking user. Only root or a user with the solaris.jobs.admin authorization can specify a username following the –l option to list the crontab file of the specified user.

–r

Removes a user's crontab from the crontab directory. Only root or a user with the solaris.jobs.admin authorization can specify a username following the –r option to remove the crontab file of the specified user.

Examples

Example 1 Cleaning up Core Files

This example cleans up core files every weekday morning at 3:15 am:


15 3 * * 1-5 find $HOME -name core 2>/dev/null | xargs rm –f 
Example 2 Mailing a Birthday Greeting

This example mails a birthday greeting:

0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.
Example 3 Specifying Days of the Month and Week

This example runs a command on the first and fifteenth of each month, as well as on every Monday:

0 0 1,15 * 1

To specify days by only one field, the other field should be set to *. For example:

0 0 * * 1

would run a command only on Mondays.

Example 4 Using Environment Variables

The following entries take advantage of crontab support for certain environment variables.

TZ=GMT
HOME=/local/home/user
SHELL=/usr/bin/ksh
0 0 * * * echo $(date) >        midnight.GMT
TZ=US/Pacific
0 0 * * * echo $(date) >        midnight.PST
TZ=US/Eastern
HOME=/local/home/myuser
SHELL=/bin/csh

The preceding entries allow two jobs to run. The first one would run at midnight in the GMT timezone and the second would run at midnight in the PST timezone. Both would be run in the directory /local/home/user using the Korn shell. The file concludes with TZ, HOME, and SHELL entries that return those variable to their default values.

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of crontab: LANG, LC_ALL , LC_CTYPE, LC_MESSAGES, and NLSPATH.

/usr/bin/crontab

EDITOR

Determine the editor to be invoked when the –e option is specified. This is overridden by the VISUAL environmental variable. The default editor is vi(1).

PATH

The PATH in crontab's environment specifies the search path used to find the editor.

VISUAL

Determine the visual editor to be invoked when the –e option is specified. If VISUAL is not specified, then the environment variable EDITOR is used. If that is not set, the default is vi(1).

/usr/xpg4/bin/crontab

EDITOR

Determine the editor to be invoked when the –e option is specified. The default editor is /usr/xpg4/bin/vi.

/usr/xpg6/bin/crontab

EDITOR

Determine the editor to be invoked when the –e option is specified. The default editor is /usr/xpg6/bin/vi.

Exit Status

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

Files

/etc/cron.d

main cron directory

/etc/cron.d/cron.allow

list of allowed users

/etc/default/cron

contains cron default settings

/etc/cron.d/cron.deny

list of denied users

/var/cron/log

accounting information

/var/spool/cron/crontabs

spool area for crontab

Attributes

See attributes(7) for descriptions of the following attributes:

/usr/bin/crontab

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os
Interface Stability
Committed
Standard

/usr/xpg4/bin/crontab

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/xopen/xcu4
Interface Stability
Standard

/usr/xpg6/bin/crontab

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/xopen/xcu6
Interface Stability
Standard

See Also

atq(1), atrm(1), auths(1), ed(1), sh(1), vi(1), auth_attr(5), attributes(7), environ(7), standards(7), cron(8), su(8)

Notes

If you inadvertently enter the crontab command with no arguments, do not attempt to get out with Control-d. This removes all entries in your crontab file. Instead, exit with Control-c.

When updating cron, check first for existing crontab entries that can be scheduled close to the time of the update. Such entries can be lost if the update process completes after the scheduled event. This can happen because, when cron is notified by crontab to update the internal view of a user's crontab file, it first removes the user's existing internal crontab and any internal scheduled events. Then it reads the new crontab file and rebuilds the internal crontab and events. This last step takes time, especially with a large crontab file, and can complete after an existing crontab entry is scheduled to run if it is scheduled too close to the update. To be safe, start a new job at least 60 seconds after the current date and time.

Simultaneous modifications of the same crontab file may lead to unexpected results.

Care should be taken when adding TZ, SHELL and HOME variables to the crontab file when the crontab file could be shared with applications that do not expect those variables to be changed from the default. Resetting the values to their defaults at the bottom of the file will minimize the risk of problems.