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User Commandscrontab(1)


 crontab - user crontab file


 crontab [filename]
 crontab [-elr] username



The crontab utility manages a user's access with cron (see cron(1M)) 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 will overwrite 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 authorization is allowed to submit a job.

Notice that 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 may 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). Note that the specification of days may 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 line beginning with a `#' is a comment and will be ignored. The file should not contain blank lines.

The shell is invoked from your $HOME directory with an arg0 of sh. Users who desire to have their .profile executed must explicitly do so in the crontab file. cron supplies a default environment for every shell, defining HOME, LOGNAME, SHELL(=/bin/sh), 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(1M).

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



The following options are supported:

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. If a username is given, the specified user's crontab file is edited, rather than the current user's crontab file; this may only be done by a user with the authorization. The environment variable EDITOR determines which editor is invoked with the -e option. The default editor is ed(1). Notice that all crontab jobs should be submitted using crontab; you should not add jobs by just editing the crontab file because cron will not be aware of changes made this way.

If all lines in the crontab file are deleted, the old crontab file will be restored. The correct way to delete all lines is to remove the crontab file via the -r option.

Lists the crontab file for the invoking user. Only a user with the authorization can specify a username following the -r or -l options to remove or list the crontab file of the specified user.
Removes a user's crontab from the crontab directory.


 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
0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.
Example 3. Specifying days of the month and week

This example
0 0 1,15 * 1
would run a command on the first and fifteenth of each month, as well as on every Monday.

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.



See environ(5) for descriptions of the following environment variables that affect the execution of crontab: LC_TYPE, LC_MESSAGES, and NLSPATH.

Determine the editor to be invoked when the -e option is specified. The default editor is ed(1). If both the EDITOR and VISUAL environment variables are set, the value of the VISUAL variable is selected as the editor.



The following exit values are returned:

Successful completion.
An error occurred.


main cron directory
list of allowed users
contains cron default settings
list of denied users
accounting information
spool area for crontab



See attributes(5) for descriptions of the following attributes:




atq(1), atrm(1), auths(1), ed(1), sh(1), cron(1M), su(1M), auth_attr(4), attributes(5), environ(5)



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

If an authorized user modifies another user's crontab file, resulting behavior may be unpredictable. Instead, the super-user should first use su(1M) to become super-user to the other user's login before making any changes to the crontab file.

When updating cron, check first for existing crontab entries that may be scheduled close to the time of the update. Such entries may 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 may 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.

SunOS 5.9Go To TopLast Changed 3 Dec 2001

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.