Checking whether there are any cronjobs currently running

Question

I'm running a webserver in a VM.

In order to create consistent backups, I have to stop Apache, MySQL and other processes for a short time before doing a snapshot of the VM's harddrive (LVM-based).

However, there might be some cronjobs currently running on the VM that need access to the MySQL database. I don't want to interrupt them.

Therefore, I'm looking for a way to determine whether there are currently any cronjobs running. When it's time for a backup, I will wait until I don't "disturb" any cronjob.

Any ideas how to accomplish this?

score 2 · Answer 1 · edited Apr 13 '17 at 12:14

2

What you really need to do is use a locking system because anything that checks for the existence/non-existence of something leaves a window of opportunity for a process to launch and create the inconsistent state you're tryiung to avoid.

Linux provides the flock command there is an example of using it here.

edited Apr 13 '17 at 12:14

Community

1

answered Mar 08 '13 at 08:08

user9517

114,104
20
206
289

score 1 · Accepted Answer · answered Mar 08 '13 at 08:21

1

if [ $(ps h --ppid `pidof crond` | wc -l) -eq 0 ]; then 
   /run/your/backup
else 
    echo "There are some still running cron jobs."
fi

answered Mar 08 '13 at 08:21

quanta

50,327
19
152
213

I guess that's better than "pgrep cron", because the latter would also find any processes that happen to have "cron" in their name, right? – David Scherfgen Mar 08 '13 at 08:36
Yes, you're right. `pgrep, pkill - look up or signal processes based on name and other attributes`. – quanta Mar 08 '13 at 08:39

Checking whether there are any cronjobs currently running

2 Answers2