crontab - Submits a schedule of commands to cron
crontab [file]
crontab -l | -v | -r | -e [username]
Interfaces documented on this reference page conform to
industry standards as follows:
crontab: XCU5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Edits a copy of your crontab entry. If the crontab entry
does not exist, creates an empty entry to edit. The -e
option invokes the editor specified by the EDITOR environment
variable, or uses /usr/bin/vi by default. The
crontab command installs the new entry when editing is
complete.
[Tru64 UNIX] If username is specified, edits the
file for the specified user. You must have appropriate
privileges to use this option. Displays the
contents of your crontab file. Removes the crontab
file from the crontab directory. [Tru64
UNIX] Displays the name of your crontab file and
the date and time at which you submitted it with
crontab.
Path name of file that contains crontab specifications in
the format described.
The crontab command copies the specified file or standard
input if you do not specify a file into the
/var/spool/cron/crontabs directory, which holds all users'
crontab files.
The cron command runs commands according to the instructions
in the crontab files. The crontab files are named
for users, and the commands in the files are run under the
user's authority. For example, the commands in the
/var/spool/cron/crontabs/root file are run under root
authority. When you use the crontab command, the file
under your authority is affected. For example, if adm
invokes the crontab -l command, the
/var/spool/cron/crontabs/adm file is displayed. If the
username argument is included, the specified user's
crontab file is listed and edited rather than the current
user's crontab file. You must have root privileges to
specify the username argument. By default, the vi editor
is used.
Note that the file /var/spool/cron/crontabs/root contains
several entries that will run by default, such as the
following command to back up and clean the /var/adm/wtmp
log file: 0 2 * * 0 /usr/bin/logclean /var/adm/wtmp >
dev/null
You can configure these default commands to suit your
local system requirements.
After cron runs commands according to the contents of your
crontab file, it mails you the output from standard output
and standard error for these commands, unless you redirect
standard output or standard error.
Note
When entries are made to a crontab file by using the
crontab command, all previous entries in the file are
removed.
You can use the crontab command if your user name appears
in the /usr/lib/cron/cron.allow file. If that file does
not exist, the crontab command checks the
/usr/lib/cron/cron.deny file to determine if you should be
denied access to crontab. The allow/deny files contain
one user name per line. If neither file exists, you can
submit a job only if you are operating with superuser
authority.
Each crontab file entry consists of a line with six
fields, separated by spaces and tabs. The information in
the fields specifies when the command runs and the name of
the command. The fields specify the following: The first
field specifies the minute (0 to 59). The second field
specifies the hour (0 to 23). The third field specifies
the day of the month (1 to 31). The fourth field specifies
the month of the year (1 to 12). The fifth field
specifies the day of the week (0 to 6 for Sunday to Saturday).
The sixth field specifies the shell command to be
executed.
You can specify the following values in the fields that
indicate the time: An integer (within the appropriate
range of values) Two integers separated by a dash to indicate
an inclusive range A list of integers separated by
commas An asterisk to select all possible values
You can specify the days on which the command is to execute
in two fields (day of the month and day of the week).
You can specify both fields, or you can specify only one
field. To use only one field to specify the days, the
other field should contain an asterisk (*). If both methods
are used, the command is executed whenever either of
the specifications is met.
[Tru64 UNIX] For example, the following entry runs command
at midnight on the first and fifteenth days of each
month, as well as every Monday: 0 0 1,15 * 1 command
The cron program runs the command named in the sixth field
at the specified date and time. If you include a percent
sign (%) in the sixth field, cron treats everything that
precedes it (in that field) as the command invocation, and
makes all that follows it available to standard input,
unless you escape the percent sign (\%) or double quote it
("%"). An exclamation point (!) in the sixth field is
translated as a newline character.
The shell runs only the first line of the command field
(up to a percent sign or End-of-Line). All other lines
are made available to the command as standard input.
The cron program invokes a subshell from your $HOME directory.
This means that it will not run your file. If you
schedule a command to run when you are not logged in and
you want to have commands in your run, you must explicitly
do so in the crontab file. (For a more detailed discussion
of how sh can be invoked, see the sh command.)
The cron program supplies a default environment for every
shell, defining HOME, LOGNAME, SHELL (=/usr/bin/sh), and
PATH (=:/usr/bin).
[Tru64 UNIX] To submit commands to the cron daemon,
invoke the crontab command with the -e option, or perform
the following tasks: [Tru64 UNIX] Become the user that
corresponds to the appropriate file in the
/usr/spool/cron/crontabs directory. For example, if you
want to submit commands that will run under adm authority,
become user adm. [Tru64 UNIX] Use the crontab command
with the -l option to copy the appropriate file from the
/usr/spool/cron/crontabs directory to a temporary file in
your home directory. For example, if you are user adm,
you could use the following command: crontab -l > temp_adm
[Tru64 UNIX] Edit the temporary file and add the commands
you want to run at a specified time. [Tru64 UNIX] Use
the crontab command and specify the temporary file to submit
the commands to the cron daemon.
When entries are made to a crontab file, all previous
entries are erased. If your user ID is associated with
more than one user name, crontab uses the first user name
that appears in the /etc/passwd file, regardless of which
user name you might actually be using. [Tru64 UNIX] The
file /usr/lib/cron is a symbolic link to /var/adm/cron.
[Tru64 UNIX] If cron.allow exists, the superuser's user
name must appear there for that superuser to be able to
use the command.
The following exit values are returned: Successful completion.
An error occurred.
The following example writes the time to the console every
hour on the hour: 0 * * * * echo The hour is `date`.
>/dev/console The following example runs calendar at 6:30
a.m. every Monday, Wednesday, and Friday: 30 6 * * 1,3,5
/usr/bin/calendar - The following example writes the contents
of happyholidays.txt to all users logged in at 4:00
p.m. each Friday in December and each day between December
10 and December 31 inclusive: 0 16 10-31 12 5
/usr/sbin/wall /var/tmp/happyholidays.txt
ENVIRONMENT VARIABLES [Toc] [Back] The following environment variables affect the execution
of crontab: Determines the editor used with the -e option.
Provides a default value for the internationalization
variables that are unset or null. If LANG is unset or
null, the corresponding value from the default locale is
used. If any of the internationalization variables contain
an invalid setting, the utility behaves as if none of the
variables had been defined. If set to a non-empty string
value, overrides the values of all the other internationalization
variables. Determines the locale for the interpretation
of sequences of bytes of text data as characters
(for example, single-byte as opposed to multibyte characters
in arguments). Determines the locale for the format
and contents of diagnostic messages written to standard
error. Determines the location of message catalogues for
the processing of LC_MESSAGES.
Main cron directory. Directory containing the crontab
files adm, cronuucp, root, sys,and uucp. List of allowed
users. List of denied users. Log of cron activity.
Queue description file for at, batch, and cron. Contains
user information. User profile.
Commands: at(1), cron(8), mail(1), mailx(1), Bourne shell
sh(1b), POSIX shell sh(1p)
Files: queuedefs(4)
Standards: standards(5)
crontab(1)
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