NAME

crontab − user crontab file

SYNOPSIS

crontab [file]
crontab −r
crontab −l

DESCRIPTION

crontab copies the specified file, or standard input if no file is specified, into a directory that holds all users’ crontabs.  The −r option removes a user’s crontab from the crontab directory.  crontab −l will list the crontab file for the invoking user. 

Users are permitted to use crontab if their names appear in the file /usr/lib/cron/cron.allow.  If that file does not exist, the file /usr/lib/cron/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 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. 

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/lib/cronmain cron directory
/usr/spool/cron/crontabsspool area
/usr/lib/cron/logaccounting information
/usr/lib/cron/cron.allowlist of allowed users
/usr/lib/cron/cron.denylist of denied users

SEE ALSO

sh(1), cron(1M), queuedefs(4)

WARNINGS

If you inadvertently enter the crontab command with no argument(s), do not attempt to get out with a CTRL-d.  This will cause all entries in your crontab file to be removed.  Instead, exit with a DEL. 

September 02, 1992