Re: Fwd: What could be causing a oneshot unit not to be run when a machine reboots?

[Andrei Borzenkov <arvidjaar@xxxxxxxxx>]

On 14.03.2021 09:03, John Ioannidis wrote:
> I have the following service file:
> 
> [Unit]
> Description=D
> After=network.target
> 
> [Service]
> ExecStart=/usr/local/sbin/mktags.py
> Type=oneshot
> User=root
> 

This is default anyway

> [Install]
> WantedBy=multi-user.target
> 
> 
> Occasionally, when the machine reboots, it does not run. Here is the
> evidence:
> 
> # uptime
> 05:50:11 up 20 min,  1 user,  load average: 0.14, 0.03, 0.01
> 
> The machine has been up for 20 minutes, so it rebooted at 05:30
> 
> # systemctl status mktags.service
> * mktags.service - D
>     Loaded: loaded (/etc/systemd/system/mktags.service; enabled; vendor
> preset: enabled)
>     Active: inactive (dead)
> 
> Weird... no indication of what the last process was... let's check
> journalctl:
> 
> # journalctl -u mktags.service | tail -4
> -- Reboot --
> Mar 14 05:25:22 sll9 systemd[1]: Starting D...
> Mar 14 05:25:22 sll9 systemd[1]: mktags.service: Succeeded.
> Mar 14 05:25:22 sll9 systemd[1]: Finished D.
> 
> The last time the service ran was five minutes *before* I rebooted. Other
> times the service runs fine. On the same machine, a bit later:
> 
> # uptime
> 05:57:31 up 2 min,  1 user,  load average: 0.31, 0.33, 0.14
> 
> 
> # systemctl status mktags.service
> * mktags.service - D
>     Loaded: loaded (/etc/systemd/system/mktags.service; enabled; vendor
> preset: enabled)
>     Active: inactive (dead) since Sun 2021-03-14 05:55:14 UTC; 2min 24s ago
>    Process: 468 ExecStart=/usr/local/sbin/mktags.py (code=exited,
> status=0/SUCCESS)
>   Main PID: 468 (code=exited, status=0/SUCCESS)
> (more output indicated that the process indeed ran).
> 

When network.target became active in each case?

> 
> 
> How do I even debug something like this? I have added code in mktags.py to
> print stuff to stderr, so that journalctl picks it up. When the service
> runs, the expected output is there. Where it does not run, it is not there
> of course.
> 
> I cannot detect any other errors elsewhere; if the service fails to start,
> and I reboot, it invariably runs then. Obviously this is not a solution;
> these are unattended machines running on GCE!
> 
> 
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