Topic 8

Dates: 3/8/2017
Start-up and Run Levels. Scheduled jobs (at, cron)
Linux System Administration

One time scheduled jobs: at

To schedule a job to run once at a particular time, use command at time_to_run, for example, to run at 8:40 am:

at 0840
Then type-in commands and finish with ^D

Time format examples:

at 1825 Mar 4
at now + 1 minute
at now + 1 hour
at now + 1 day 

To run an executable file or a script:

at -f filename time_to_run 
For example,

at -f /home/jerry/ 2030
at -f /home/jerry/ 11am Mar 30 

Command at puts a scheduled job in a queue in /var/spool/at/; daemon /usr/sbin/atd checks for queued jobs in that directory and runs them.

To check scheduled job status, run

To delete scheduled job, run


Permssions on using at:
  • If /etc/at.allow does not exist, /etc/at.deny is checked, every user name not mentioned in it is then allowed to use at.
  • If neither exists, only the superuser is allowed use of at.
  • An empty /etc/at.deny means that every user is allowed use these commands.

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