[Lxc-users] upstart /etc/init/screen-cleanup.conf

[Trent W. Buck]

"Serge E. Hallyn" <serge.hallyn at canonical.com>
writes:

> Quoting Trent W. Buck (trentbuck at gmail.com):
>> A race condition in my containers means that occasionally
>> /var/run/screen/ isn't present when startup finishes and I SSH in.
>> This results in an error when normal users try to run screen.
>> 
>> I believe the race is against my lxc integration job:
>> 
>>     root at imago:~# cat /etc/init/lxc.conf
>>     start on startup
>>     task
>>     script
>>     [...]
>>      find /var/run/ -xdev -not -path /var/run/ -delete
>> 
>> The screen-cleanup job is
>> 
>>     root at imago:~# grep -v ^$ /etc/init/screen-cleanup.conf
>>     start on filesystem
>>     task
>>     script
>>       SCREENDIR=/var/run/screen
>>       if [ -L $SCREENDIR ] || [ ! -d $SCREENDIR ]; then
>>         rm -f $SCREENDIR
>>         mkdir $SCREENDIR
>>         chown root:utmp $SCREENDIR
>>       fi
>>       [...]
>> 
>> Obviously the *right* solution is to use a tmpfs for /var/run, as
>> non-containerized Ubuntu does.  Since this breaks lxc-start's
>> reboot/halt (via utmp) detection, I'm looking for the next best
>> workaround.
>> 
>> I think this is probably to disable /etc/init/mountall.conf and spoof
>
> If you're saying that what you need is for this to run before mountall.conf,
> then you can make sure that screen-cleanup.conf finishes before mountall
> starts by making it
>
> 	start on starting mountall
>
> Then it will finish before mountall really starts.

screen-cleanup creates /var/run/screen -- it needs to run *after*
lxc.conf deletes everything in /var/tmp.  It (lxc) does that to simulate
mounting a tmpfs on /var/run, which is something the mountall job
normally does, and what it normally emits a filesystem event after.

But with the lxc job above, /var/run is deleted asynchronously from the
mountall run, meaning that screen-cleanup can earlier.  Changing
screen-cleanup to depend on anything mountall emits wouldn't help,
AFAICT -- and more to the point, it'd only fix screen-cleanup and not
arbitrary other jobs that might be created when a new package is
installed.