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Old 11-24-2016, 07:50 PM   #1
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Learning cron : CentOS7 : anacron and cron

Both anacron and cron are up, but in sleep at this point:

[user1@server1 cron.hourly]$ ps aux | grep -i anacron
root      4261  0.0  0.0 123308   740 ?        Ss   12:01   0:00 /usr/sbin/anacron -s
user1     5084  0.0  0.0 112648   948 pts/0    R+   12:24   0:00 grep --color=auto -i anacron
[user1@server1 cron.hourly]$ ps aux | grep -i crond
root      1331  0.0  0.1 126332  1660 ?        Ss   11:42   0:00 /usr/sbin/crond -n
user1     5089  0.0  0.0 112648   948 pts/0    R+   12:24   0:00 grep --color=auto -i crond
From man anacron page"
       Anacron  is  used  to  execute  commands periodically, with a frequency
       specified in days.  Unlike cron(8), it does not assume that the machine
       is  running  continuously.   Hence, it can be used on machines that are
       not running 24 hours a day to control regular jobs  as  daily,  weekly,
       and monthly jobs.

       Anacron  reads  a  list  of jobs from the /etc/anacrontab configuration
       file (see anacrontab(5)).  This file contains the  list  of  jobs  that
       Anacron  controls.   Each job entry specifies a period in days, a delay
       in minutes, a unique job identifier, and a shell command.

       For each job, Anacron checks whether this job has been executed in  the
       last  n  days, where n is the time period specified for that job.  If a
       job has not been executed in n days or more,  Anacron  runs  the  job's
       shell command, after waiting for the number of minutes specified as the
       delay parameter.

       After the command exits, Anacron records the date (excludes  the  hour)
       in  a  special timestamp file for that job, so it knows when to execute
       that job again.
And from man cron page:

.......In case systemd is enabled, then  unit  file
       is  installed  into  /lib/systemd/system/crond.service  and  daemon  is
       started by systemctl start crond.service command.  It  returns  immedi‐
       ately,  thus, there is no need to need to start it with the '&' parame‐

       Cron searches /var/spool/cron for crontab files which are  named  after
       accounts in /etc/passwd; The found crontabs are loaded into the memory.
       Cron also searches for /etc/anacrontab and any files in the /etc/cron.d
       directory,  which have a different format (see crontab(5)).  Cron exam‐
       ines all stored crontabs and checks each job to see if it needs  to  be
       run  in  the  current  minute.   When executing commands, any output is
       mailed to the owner of the crontab (or to the  user  specified  in  the
       MAILTO  environment  variable in the crontab, if such exists).  Any job
       output can also be sent to syslog by using the -s option.

Since cron and anacron also checks /etc/anacrontab,
Q1: How do they resolve not executing /etc/anacrontab twice?

Q2: I am not able to find how anacron was started using: systemctl --all.

How do I find out how anacron was started and by who?
man anacron did not help much.


Last edited by fanoflq; 11-24-2016 at 08:03 PM.
Old 11-24-2016, 09:31 PM   #2
Registered: Aug 2002
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anacron is not a service and is started by cron.
1 members found this post helpful.
Old 11-24-2016, 09:50 PM   #3
Registered: Nov 2015
Posts: 397

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Originally Posted by michaelk View Post
anacron is not a service and is started by cron.
Thank you.


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