CRONTAB(1)CRONTAB(1)NAMEcrontab - user crontab file
SYNOPSIScrontab [file]
crontab-r [file]
crontab-l [file]
crontab-e [file]
DESCRIPTIONcrontab 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. The -e option spawns an
editor which contains the user's current crontab (as output by crontab
-l), and automatically updates the crontab when the user saves the file
and exits the editor. The name of the editor to invoke can be specified
by the environment variable VISUAL or EDITOR; else, vi is used by
default.
Normal users may only remove, list, or edit their own crontab files which
is the default. The superuser (root) may supply any username following
-r, -l, or -e to remove, list, or edit that user's crontab.
If the file /etc/cron.d/cron.allow exists, only users whose names appear
in the file are permitted to use crontab. This restriction applies to all
users, including root. If that file does not exist, the file
/etc/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 would run a command only on Mondays).
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CRONTAB(1)CRONTAB(1)
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, USER, SHELL(=/bin/sh),
PATH(=/usr/sbin:/usr/bsd:/sbin:/usr/bin:/etc:/usr/etc:/usr/bin/X11), and
TZ.
If you do not redirect the standard output and standard error of your
commands, any generated output or errors will be mailed to you.
Any errors encountered while parsing the crontab file (or stdin) will
cause crontab to abort with no changes being made to any existing
crontab.
FILES
/etc/cron.d main cron directory
/var/spool/cron/crontabs spool area
/var/cron/log accounting information
/etc/cron.d/cron.allow optional list of allowed users
/etc/cron.d/cron.deny list of denied users
/etc/cron.d/FIFO to communicate crontab changes to cron
SEE ALSOsh(1), cron(1M)NOTES
If you inadvertently enter the crontab command with no argument(s), you
may exit without overwriting the existing crontab entry either by
generating an interrupt (typically by typing ^C or DEL), or by providing
empty input (typically by typing ^D on the first empty line).
If a job is scheduled during the 'witching hour' - the time during a
change from the main to alternate time zone, the job will either be run
once (if the actual time exists twice) or not at all (if the actual time
never exists).
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