The following sections describe how to use the at command to perform the following tasks:
Schedule jobs (command and scripts) for execution at a later time
How to display and remove these jobs
How to control access to the at command
By default, users can create, display, and remove their own at job
files. To access at files that belong to root or
other users, you must have superuser privileges.
When you submit an at job, it is assigned a job identification
number along with the .a extension. This designation becomes
the job's file name, as well as its queue number.
Submitting an at job file involves these steps:
Invoking the at utility and specifying a command execution time.
Typing a command or script to execute later.
If output from this command or script is important, be sure to direct the output to a file for later examination.
For example, the following at job removes core files from the user account smith near midnight
on the last day of July.
$at 11:45pm July 31at>rm /home/smith/*core*at>Press Control-dcommands will be executed using /bin/csh job 933486300.a at Tue Jul 31 23:45:00 2004
You can set up a file to control access to the at command,
permitting only specified users to create, remove, or display queue information about
their at jobs. The file that controls access to the at command, /etc/cron.d/at.deny, consists of a list of
user names, one user name per line. The users who are listed in this file cannot access at commands.
The at.deny file, which is created during SunOS software
installation, contains the following user names:
daemon bin smtp nuucp listen nobody noaccess
With superuser privileges, you can edit the at.deny file
to add other user names whose at command access you want to restrict.
How to Create an at Job
Start the at utility, specifying the time you want your job executed.
$at[-m]time[date]
Sends you email after the job is completed.
time
Specifies the hour that you want to schedule the job. Add am or pm if you do not specify the hours according to
the 24-hour clock. Acceptable keywords are midnight, noon, and now. Minutes are optional.
date
Specifies the first three or more letters of a month, a day of the
week, or the keywords today or tomorrow.
At the at prompt, type the commands or scripts that you want to execute, one per line.
You may type more than one command by pressing Return at the end of each line.
Exit the at utility and save the at job by pressing Control-D.
Your at job is assigned a queue number, which is also the job's file name. This number is displayed when you exit the at utility.
Example 15.7. Creating an at Job
The following example shows the at job that user jones created to remove her backup files at 7:30 p.m. She used the
m option so that she would receive an email message after her job completed.
$at -m 1930at>rm /home/jones/*.backupat>Press Control-Djob 897355800.a at Thu Jul 12 19:30:00 2004
She received a email message which confirmed the execution of her at job.
Your “at” job “rm /home/jones/*.backup”
completed.
The following example shows how jones scheduled a large at job for 4:00 a.m. Saturday morning. The job output was directed to a
file named big.file.
$at 4 am Saturdayat>sort -r /usr/dict/words > /export/home/jones/big.file
How to Verify an at Job
To verify that you have created an at job, use the atq command. In the following example, the atq command
confirms that at jobs that belong to jones have
been submitted to the queue.
$ atq
Rank Execution Date Owner Job Queue Job Name
1st Jul 12, 2004 19:30 jones 897355800.a a stdin
2nd Jul 14, 2004 23:45 jones 897543900.a a stdin
3rd Jul 17, 2004 04:00 jones 897732000.a a stdin
How to Display at Jobs
To display information about the execution times of your at jobs, use the at -l command.
$at -l[job-id]
where the
l job-id option identifies
the identification number of the job whose status you want to display.
Example 15.8. Displaying at Jobs
The following example shows output from the at -l command, which provides information on the status of all jobs submitted by a user.
$ at -l
897543900.a Sat Jul 14 23:45:00 2004
897355800.a Thu Jul 12 19:30:00 2004
897732000.a Tue Jul 17 04:00:00 2004
The following example shows the output that is displayed when a single job is specified with the at -l command.
$ at -l 897732000.a
897732000.a Tue Jul 17 04:00:00 2004
How to Remove at Jobs
Become superuser or assume an equivalent role to remove an at job
that belongs to root or another user. Roles contain authorizations
and privileged commands. For more information about roles, see
Configuring RBAC (Task Map) in System Administration Guide: Security Services
.
You do not need to become superuser or assume an equivalent role to remove your
own at job.
Remove the at job from the queue before the job is executed.
$at -r[job-id]
where the
r job-id option specifies
the identification number of the job you want to remove.
Verify that the at job is removed by using the at -l (or the atq) command.
The at -l command displays the jobs remaining in the at queue. The job whose identification number you specified should not appear.
$at -l[job-id]
Example 15.9. Removing at Jobs
In the following example, a user wants to remove an at job that was scheduled to execute at 4 a.m. on July 17th. First, the user displays the at queue to locate the job identification number. Next, the user removes this job from the at queue. Finally, the user verifies that this job has been removed from the queue.
$at -l897543900.a Sat Jul 14 23:45:00 2003 897355800.a Thu Jul 12 19:30:00 2003 897732000.a Tue Jul 17 04:00:00 2003 $at -r 897732000.a$at -l 897732000.aat: 858142000.a: No such file or directory
How to Deny Access to the at Command
Become superuser or assume an equivalent role.
Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services .
Edit the /etc/cron.d/at.deny file
and add the names of users, one user name per line, that will be prevented from using
the at commands.
daemon bin smtp nuucp listen nobody noaccessusername1username2username3. . .
How to Verify That at Command Access Is Denied
To verify that a username was added correctly to the /etc/cron.d/at.deny file, use the at -l command while logged in as the
user. If the user smith cannot access the at command,
the following message is displayed.
#su smithPassword: $at -lat: you are not authorized to use at. Sorry.
Likewise, if the user tries to submit an at job, the following message is displayed:
$ at 2:30pm
at: you are not authorized to use at. Sorry.
This message confirms that the user is listed in the at.deny file.
If at command access is allowed, then the at -l command returns nothing.