 |
Click this button to go to the index for this section. |
crontab(1)
NAME
crontab - Submits a schedule of commands to cron
SYNOPSIS
crontab [file]
crontab -l|-v|-r|-e [username]
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
crontab: XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
-e [username]
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.
[DIGITAL] If username is specified, edits the file for the specified
user. You must have appropriate privileges to use this option.
-l Displays the contents of your crontab file.
-r Removes the crontab file from the crontab directory.
-v [DIGITAL] Displays the name of your crontab file and the date and time
at which you submitted it with crontab.
OPERANDS
file
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 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.
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.
[DIGITAL] 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 .profile file. If you schedule a command to run
when you are not logged in and you want to have commands in your .profile
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).
[DIGITAL] To submit commands to the cron daemon, invoke the crontab
command with the -e option, or perform the following tasks:
1. [DIGITAL] 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.
2. [DIGITAL] 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
3. [DIGITAL] Edit the temporary file and add the commands you want to
run at a specified time.
4. [DIGITAL] Use the crontab command and specify the temporary file to
submit the commands to the cron daemon.
NOTES
1. When entries are made to a crontab file, all previous entries are
erased.
2. 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.
3. [DIGITAL] The file /usr/lib/cron is a symbolic link to /var/adm/cron.
4. [DIGITAL] 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:
0 Successful completion.
>0 An error occurred.
EXAMPLES
1. The following example writes the time to the console every hour on the
hour:
0 * * * * echo The hour is `date`. >/dev/console
2. The following example runs calendar at 6:30 a.m. every Monday,
Wednesday, and Friday:
30 6 * * 1,3,5 /usr/bin/calendar -
3. 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:
EDITOR
Determines the editor used with the -e option.
LANG
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.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
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).
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
Determines the location of message catalogues for the processing of
LC_MESSAGES.
FILES
/var/spool/cron/crontabs
Directory containing the crontab files.
/var/adm/cron/cron.allow
List of allowed users.
/var/adm/cron/cron.deny
List of denied users.
/var/adm/cron/log
Log of cron activity.
/etc/passwd
Contains user information.
$HOME/.profile
User profile.
SEE ALSO
Commands: at(1), cron(8), mail(1), mailx(1), Bourne shell sh(1b), POSIX
shell sh(1p)
Standards: standards(5)