crontab(1)crontab(1)NAMEcrontab - Submits a schedule of commands to cron
SYNOPSIScrontab [file]
crontab-l | -v | -r | -e [username]
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
crontab: XCU5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
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.
OPERANDS
Path name of file that contains crontab specifications in the format
described.
DESCRIPTION
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 com‐
mands 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 com‐
mand, the /var/spool/cron/crontabs/adm file is displayed. If the user‐
name 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 fol‐
lowing: 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 spec‐
ified 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 per‐
cent 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, defin‐
ing 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 appropri‐
ate 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.
NOTES
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.
EXIT STATUS
The following exit values are returned: Successful completion. An
error occurred.
EXAMPLES
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
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 argu‐
ments). Determines the locale for the format and contents of diagnos‐
tic messages written to standard error. Determines the location of
message catalogues for the processing of LC_MESSAGES.
FILES
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.
SEE ALSO
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)
