crontab(1) (User Environment Utilities) crontab(1)
NAME
crontab - user crontab file
SYNOPSIS
crontab [file]
crontab -e [ username ]
crontab -r [ username ]
crontab -l [ username ]
DESCRIPTION
crontab copies the specified file, or standard input if no file is
specified, into a directory that holds all users' crontabs. The -e
option 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 privileged user. The environment variable EDITOR determines which
editor is invoked with the -e option. The default editor is vi(1).
The -r option removes a user's crontab from the crontab directory.
crontab -l will list the crontab file for the invoking user. Only a
privileged user can specify a username following the -r or -l options
to remove or list the crontab file of the specified user.
Users are permitted to use crontab if their names appear in the file
/usr/sbin/cron.d/cron.allow. If that file does not exist, the file
/usr/sbin/cron.d/cron.deny is checked to determine if the user should
be denied access to crontab. If neither file exists, only root is
allowed to submit a job. If cron.allow does not exist and cron.deny
exists but is empty, global usage is permitted. The allow/deny files
consist of one user name per line.
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). If both are
specified as a list of elements, both are adhered to. For 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
7/91 Page 1
crontab(1) (User Environment Utilities) crontab(1)
would run a command only on Mondays).
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 new-line
character. Only the first line (up to a % or end of line) of the
command field is executed by the shell. The other lines are made
available to the command as standard input.
Any line beginning with a # is a comment and will be ignored.
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), and
PATH(=:/bin:/usr/bin:/usr/lbin).
If you do not redirect the standard output and standard error of your
commands, any generated output or errors will be mailed to you.
FILES
/usr/sbin/cron.d main cron directory
/var/spool/cron/crontabsspool area
/usr/sbin/cron.d/logaccounting information
/usr/sbin/cron.d/cron.allowlist of allowed users
/usr/sbin/cron.d/cron.denylist of denied users
SEE ALSO
atq(1), atrm(1), sh(1), su(1), vi(1).
cron(1M) in the System Administrator's Reference Manual.
WARNINGS
If you inadvertently enter the crontab command with no argument(s),
do not attempt to get out with a CONTROL-D. This will cause all
entries in your crontab file to be removed. Instead, exit with a
DEL.
If a privileged user modifies another user's crontab file, resulting
behavior may be unpredictable. Instead, the privileged user should
first su(1M) to the other user's login before making any changes to
the crontab file."
Page 2 7/91