[lxc-users] OOMScoreAdjust= in dbus.service on systemd-based unprivileged containers

[Serge Hallyn]

https://www.mail-archive.com/systemd-devel@lists.freedesktop.org/msg26524.html

?

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> Hello,
> 
> In the past I had troubles getting systemd-based unprivileged containers
> such as Archlinux or Debian Jessie to boot. On the other hand some
> systemd-based unpriv. containers such as Ubuntu Vivid worked fine and
> out of the box. (But I remember Stephane once saying that they were
> somehow patched.)
> 
> With a little trick I can now also get Archlinux unpriv. containers
> booting out of the box, meaning I pacstrap a file-system and then use
> uidmapshift to map ids and gids or create a privileged one with the LXC
> template and then uidmapshift them.
> 
> For this to work the dbus.service file in the unpriv.  Archlinux
> container under /usr/lib/systemd/system/ must be patched. It contains
> the entry:
> 
>     OOMScoreAdjust=-900
> 
> where OOMScoreAdjust
> 
>     "Sets the adjustment level for the Out-Of-Memory killer for executed
>     processes. Takes an integer between -1000 (to disable OOM killing
>     for this process) and 1000 (to make killing of this process under
>     memory pressure very likely). See proc.txt for details."
> 
> (I won't get into detail here as all the relevant parts can be found
> under: https://www.kernel.org/doc/Documentation/filesystems/proc.txt)
> 
> The OOMScoreAdjust score of each process can be seen by doing
> 
>     cat /proc/PID/oom_adj
>     cat /proc/PID/oom_score
>     cat /proc/PID/oom_score_adj
> 
> E.g. the values for dbus-daemon on an Archlinux host will look like
> this:
> 
>     cat /proc/PID/oom_adj
> 
> will be -15 (It is only there for backwards compatibility with older
> kernels where the oom adjustement was made there.).
> 
>     cat /proc/PID/oom_adj_score
> 
> will be -900 as specified in dbus.service on Archlinux.
> 
> Finally,
> 
>     cat /proc/PID/oom_score
> 
> will be 0.
> 
> Both values, -15 and -900 make dbus one of the few processes that is
> killed last when out of memory.
> 
> All unprivileged containers I have run so far (Ubuntu Vivid, Debian
> Jessie) even though they may have the line OOMScoreAdjust in their
> dbus.service file do not adjust this value meaning when they boot they
> show 0 on all three fields under proc.
> 
> When disabling OOMScoreAdjust in the Archlinux dbus.service file of the
> unpriv. container the boot will be immediately succesfull and all three
> values under proc will show 0 just as for an Ubuntu Vivid or Debian
> Jessie unpriv. container.
> 
> So it seems that during boot systemd in Archlinux is trying to adjust
> the oom score under its /proc tree for dbus but somehow fails.
> 
> Maybe this will help some people. Should I also file this on LXC github?
> 
> Best,
> Christian



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