Wednesday, December 11, 2013

Use "at" command to schedule execute job on LINUX

 at and batch read commands from standard input or a specified file which are to be executed at a later time, using /bin/sh.

       at      executes commands at a specified time.

       atq     lists  the  user's  pending jobs, unless the user is the superuser; in that case, everybody's jobs are listed.  The format of
               the output lines (one for each job) is: Job number, date, hour, queue, and username.

       atrm    deletes jobs, identified by their job number.

       batch   executes commands when system load levels permit; in other words, when the load average drops below 1.5, or the value  speci‐
               fied in the invocation of atd.

       At  allows  fairly complex time specifications, extending the POSIX.2 standard.  It accepts times of the form HH:MM to run a job at a
       specific time of day.  (If that time is already past, the next day is assumed.)  You may also  specify  midnight,  noon,  or  teatime
       (4pm) and you can have a time-of-day suffixed with AM or PM for running in the morning or the evening.  You can also say what day the
       job will be run, by giving a date in the form month-name day with an optional  year,  or  giving  a  date  of  the  form  MMDD[CC]YY,
       MM/DD/[CC]YY,  DD.MM.[CC]YY  or [CC]YY-MM-DD.  The specification of a date must follow the specification of the time of day.  You can
       also give times like now + count time-units, where the time-units can be minutes, hours, days, or weeks and you can tell  at  to  run
       the job today by suffixing the time with today and to run the job tomorrow by suffixing the time with tomorrow.

       For  example, to run a job at 4pm three days from now, you would do at 4pm + 3 days, to run a job at 10:00am on July 31, you would do
       at 10am Jul 31 and to run a job at 1am tomorrow, you would do at 1am tomorrow.

       The definition of the time specification can be found in /usr/share/doc/at/timespec.

       For both at and batch, commands are read from standard input or the file specified with the -f  option  and  executed.   The  working
       directory, the environment (except for the variables BASH_VERSINFO, DISPLAY, EUID, GROUPS, SHELLOPTS, TERM, UID, and _) and the umask
       are retained from the time of invocation.

       As at is currently implemented as a setuid program, other environment variables (e.g.  LD_LIBRARY_PATH or LD_PRELOAD)  are  also  not
       exported.  This may change in the future.  As a workaround, set these variables explicitly in your job.

       An  at  -  or  batch - command invoked from a su(1) shell will retain the current userid.  The user will be mailed standard error and
       standard output from his commands, if any.  Mail will be sent using the command /usr/sbin/sendmail.  If at is executed from  a  su(1)
       shell, the owner of the login shell will receive the mail.

       The superuser may use these commands in any case.  For other users, permission to use at is determined by the files /etc/at.allow and
       /etc/at.deny.  See at.allow(5) for details.




EXAMPLE : to shutdown the computer in 3 minutes

root@localhost # at now + 3 minutes
warning: commands will be executed using /bin/sh
at> power
at> <EOT>           (ctrl + d: to save and exit the "at" shell)
job 25 at Wed Dec 11 11:56:00 2013
root@localhost #





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