Task scheduling (Lec13)

Task Scheduling

1. one time execution == (at,batch) is good to use

2. Recurring execution == want to execute every certain moment (cron, anacron) is good to use

at == you need to give the time to execute this command

batch == you don't need to specify time.  executes command when system load is below certain level. when the load average drops below 1.5 or the value specified in the invocation of atd.

cron == a daemon used to run scheduled tasks such as system backups, updates. it is suitable for running scheduled tasks on machines that will run continuously 24x7 such as servers. minimum term is 1minute

anacron == run commands periodically with a frequency defined in days. it assume that a machien will not be powered on all the time. minimum term is 1day. even though machine is off and later on you power on the machine anacron will execute the backup script.

 

crontab

 

always need to edit with "crontab -e" command 

cron.d == directory which contains script that have to be exectue every minute

cron.daily == every day ...