illumos: manual page: crontab.1

CRONTAB(1) User Commands CRONTAB(1)

NAME

crontab - user crontab file

SYNOPSIS

/usr/bin/crontab [-u username] [filename]

/usr/bin/crontab { -e | -l | -r } [username]

/usr/bin/crontab -u username { -e | -g | -l | -r }

/usr/xpg4/bin/crontab [filename]

/usr/xpg4/bin/crontab { -e | -g | -l | -r } [username]

/usr/xpg4/bin/crontab -u username { -e | -l | -r }

/usr/xpg6/bin/crontab [filename]

/usr/xpg6/bin/crontab { -e | -g | -l | -r } [username]

/usr/xpg6/bin/crontab -u username { -e | -l | -r }

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, or for the user specified with the -u
option.

Cron supports a merged crontab with entries coming from either the user's
/var/spool/cron/crontabs file or from the user's /etc/cron.d/crontabs
file. The entries in the user's /var/spool/cron/crontabs file are
editable whereas those in /etc/cron.d/crontabs are system-defined entries
which may not be customized by the user. The dual set of crontab entries
is only of interest to system-defined users such as root. Except where
otherwise explicitly indicated, all variants of the crontab command act
only on the editable crontab files found in /var/spool/cron/crontabs.

crontab Access Control
Users: Access to crontab is allowed:

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

o 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:

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

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

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

o if 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 hyphen (meaning an inclusive range).

A range or asterisk can optionally be followed by a step value as
/<number>. For example, 2-59/3 can be used in the minutes field to
specify every three minutes starting at 2 past the hour, or */2 in the
hours field means every two hours.

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 his .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 an 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

RANDOM_DELAY

Allows the user to specify an upper bound in minutes for which
execution may be delayed. The default is 0 which means no delay. A
value that is larger than the scheduled interval may result in the
command running less often. For example, to have the command run at
some random time within two minutes after the schedule use:

RANDOM_DELAY=2

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.

Only the entries in the user's /var/spool/cron/crontabs file are
editable.

-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.

Entries from the user's /var/spool/cron/crontabs file are listed,
unless the -g option is given, in which case only entries from the
user's /etc/cron.d/crontabs file are listed.

-g
In conjunction with the -l option, lists the global crontab file
for the invoking or specified user (if authorized) instead of the
editable crontab file. This option is not valid unless the -l
option is also given.

-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.

-u username
Specifies the name of the user whose crontab is to be replaced,
viewed or modified. This can only be done by root or by a user with
the solaris.jobs.admin authorization.

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 -namecore 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 step values:

This example runs a job every hour during the night and every 3 hours
during working hours.

0 8-18/3,19-7 * * *

and to run a job every 2 minutes, use:

*/2 * * * *

Example 5: 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=PST
0 0 * * * echo $(date) > midnight.PST
TZ=EST
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

/etc/cron.d/crontabs
system spool area for crontab

/var/cron/log
accounting information

/var/spool/cron/crontabs
spool area for crontab

ATTRIBUTES

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.

If an authorized user other than root modifies another user's crontab
file, the resulting behavior can be unpredictable. Instead, the
authorized user should first use su(8) to become superuser to the other
user's login before making any changes to the crontab file.

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.

January 9, 2022 CRONTAB(1)