Comments (3)
micschk
commented on September 27, 2024
1
What do you mean by 'running separate from Apache'? Because I think any the cronjobs you're editing are those of the user which Apache is running PHP as anyway, also 'at' does its best to copy the whole environment for the command to be run in later.
I've just removed the whole dependency on the 'at' command (doesn't work on OSX, my dev box), and changed the Crontab::run() to: sprintf("sh -c "%s" > /dev/null 2>&1 &", $command)
Then, $process->run(); instead of $process->start();, as start() doesn't seem to move it to leave the command running in the background after returning from php (this could be the reason for any unreliable behaviour, eg when the function returns before the $process->start() has finished (should call $process->wait() for this)).
$process->run() with the background command seems to work fine. If you would like, I can PR my changes.
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bogdanghervan
commented on September 27, 2024
@micschk, thank you for your detailed note!
What do you mean by 'running separate from Apache'?
What I was trying to achieve is "detach" any commands being run from the Apache process triggering them, so whenever you would restart Apache your jobs would still run and not be killed pending the restart, since whenever Apache is stopped or restarted, all processes in the process group (see PGID below) receive a SIGTERM, including those launched by CronKeep.
Here's a short experiment running a script called test.sh that sleeps for 10 minutes when launched (/var/www/test.sh 2>&1 | logger -ttest).
Launched from CronKeep without at:
$ ps axfj # output truncated for brevity
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
1 2881 2881 2881 ? -1 Ss 0 0:00 /usr/sbin/apache2 -k start
2881 2884 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2885 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2886 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2887 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2888 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2901 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2903 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2904 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2905 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2906 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2907 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
2881 2908 2881 2881 ? -1 S 33 0:00 \_ /usr/sbin/apache2 -k start
1 2914 2881 2881 ? -1 S 33 0:00 /bin/bash /var/www/test.sh
2914 2918 2881 2881 ? -1 S 33 0:00 \_ sleep 600
1 2915 2881 2881 ? -1 S 33 0:00 logger -ttest
Launched from CronKeep with at:
$ ps axfj # output truncated for brevity
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
1 2985 2985 2985 ? -1 Ss 1 0:00 atd
2985 3005 2985 2985 ? -1 S 1 0:00 \_ atd
3005 3006 2985 2985 ? -1 SN 33 0:00 \_ sh
3006 3007 2985 2985 ? -1 SN 33 0:00 \_ /bin/bash /var/www/test.sh
3007 3011 2985 2985 ? -1 SN 33 0:00 | \_ sleep 600
3006 3008 2985 2985 ? -1 SN 33 0:00 \_ logger -ttest
Admittedly the job moves under atd (the at daemon) and people can restart Apache freely, which they probably do more often than they care about atd.
The same job launched by the cron daemon:
$ ps axfj # output truncated for brevity
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
1 2651 2651 2651 ? -1 Ss 0 0:00 cron
2651 3031 2651 2651 ? -1 S 0 0:00 \_ CRON
3031 3032 3032 3032 ? -1 Ss 33 0:00 \_ /bin/sh -c /var/www/test.sh 2>
3032 3033 3032 3032 ? -1 S 33 0:00 \_ /bin/bash /var/www/test.sh
3033 3037 3032 3032 ? -1 S 33 0:00 | \_ sleep 600
3032 3034 3032 3032 ? -1 S 33 0:00 \_ logger -ttest
We can see how the job spawned by the cron service gets its very own session (see column SID). This means that when we stop cron orphaned processes will be inherited by init and keep on running:
$ service cron stop
$ ps axfj # output truncated for brevity
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
1 3032 3032 3032 ? -1 Ss 33 0:00 /bin/sh -c /var/www/test.sh 2>&1 | log
3032 3033 3032 3032 ? -1 S 33 0:00 \_ /bin/bash /var/www/test.sh
3033 3037 3032 3032 ? -1 S 33 0:00 | \_ sleep 600
3032 3034 3032 3032 ? -1 S 33 0:00 \_ logger -ttest
I think what we really need is wrap the job being called by a script which calls setsid or setpgid as it starts, to make that process a session leader (or group leader respectively). I will experiment around and come back with my findings since I'd also like to get rid of the dependency on at.
Also, please note that we cannot afford to wait for a cron job to finish in the CronKeep UI since people can have long-running scripts that can run for hours.
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RaspiGuru
commented on September 27, 2024
Hi micschk,
I made changes according to your comments (commented on 24 Nov 2016) and everything woks fine.
Great thanks
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