Linux: Process scheduling

Process scheduling using # at:

1. Executing only once can be performed through # at command.
2. Executing recursively through # crontab command

# at
command execute the tasks only once.
Syn: # at
Eg: # at 1055
at>

Control+d = to save the contents

# service atd restart
to restart the daemon.

# at -l
# atq
will display the "at" schedules in the queue.

# atrm
Eg: # atrm 4
To remove the at schedule from the task



/etc/at.deny
1. This file will be present by default.
2. Will NOT have any entry to the file.
3. Once if the user login name is added to this file,
the specified user(s) is denied to use the command at.


/etc/at.allow
1. This file will NOT be present by default.
2. Root user is given the right to create the file.
3. Once if the user login name is added to this file, only the specified user(s) are allowed to use the command.
4. When the /etc/at.allow file exists, OS reads this file and /etc/at.deny file will NOT be read.



NOTE:
In case a user has the entry in both the file, the user is ALLOWED to execute the at command.

# rpm -qa at*
displays whether the package is installed or not

at package: at-3.1.8-60

at options:
at now => execute the task now
at now +2hrs => execute the task after 2 hours
at next week => to execute the task by next week
at 12pm => to execute the task by 12pm
at 12pm june 23 2009 => to execute the task by 12 pm on june 23 2009
at next month => to execute the task by next month
at next min => to execute the task by next minute
at 10pm sunday => to execute the task by 10pm on sunday

The at tasks stored to the following path
/var/spool/at