Changing elogind IPCRemove default.

[Mark Hindley]

On Fri, Jan 24, 2020 at 03:22:06PM +0100, Thorsten Glaser wrote:
> On Fri, 24 Jan 2020, Mark Hindley wrote:
> 
> > This is essential for his usage.
> 
> Not just that, it is also essential to not break programs using
> shared memory as well, which I mentioned.

I fully understand that.

That is not really the question here. I am really asking if changing the default
might have any downsides.
 
> > In bug #949698, the reporter is demanding that we change the default for
> > IPCRemove from true to false so that /dev/shm is not cleared on user logout.
> 
> This is just a workaround anyway. The *proper* fix is to only remove
> those files from /dev/shm/ which elogind itself (or something on its
> behalf) created and leave everything else alone, of course.

I am not sure that is correct. 

For good or bad, it appears the behaviour of RemoveIPC originates in
systemd. See

 https://github.com/systemd/systemd/issues/2039

elogind is not trying to clear up after itself (AFAIK it creates no files in
/dev/shm), it is actively limiting the use of resources after a user logs out.

The NEWS file says

 'Traditionally, SysV and POSIX IPC had no life-cycle limits. With this
 functionality, that is corrected. This may be turned off by using the
 RemoveIPC= switch of logind.conf'

I am explicitly *not* arguing that this view is correct. I just want us to fully
understand the implications of changing the default when it is easy for the
sysadmin to configure the behaviour as they want.

Thanks

Mark