Re: Why do we have to support tmpfs for /var/run (policy changes in 3.8.1)
Michael Biebl <biebl@debian.org> writes:
> Why is a system service that is started by inetd or D-Bus not a daemon?
> Remember the times when exim4 or samba could still be started via inetd
> (although those no longer support inetd mode afaik).
Why would you store your PID somewhere if you're started from inetd
(that's the main thing daemons use it for)? There's nothing to manage;
when you're running in inetd mode, you process one connection and exit.
There's no purpose served by storing the PID anywhere (and indeed since
multiple copies can be running at the same time, it's not clear how you
would even do such a thing).
> There are still daemons though (like proftpd comes to mind), which ship a
> subdirectory in /var/run and support inetd.
What does it use the directory for?
> PolicyKit stores credentials in /var/run/PolicyKit which are of
> temporary nature and are automatically cleaned up on boot.
Oh, okay, so you're similar to sudo where you're taking advantage of the
fact that /var/run is cleaned on boot but isn't world-writable.
sudo appears to create its directory dynamically if it doesn't already
exist. I assume the reason why you can't take that approach is that
PolicyKit doesn't run as root and hence can't create directories in
/var/run?
I believe the original motivation for tmpfs /var/run in Solaris was that
it was pointless to maintain scripts that try to clean /var/run (or /tmp
or any other defined-transient directory) on boot, which can be dangerous
and tricky if you don't write them carefully, when you can just put them
in tmpfs and have the cleaning happen automatically without doing any
work. It simplifies the boot process and eliminates a whole class of
potential directory traversal races that you otherwise have to think
about. Potential additional boot speed from writing all the startup PID
files to a tmpfs file system (and benefits for flash drives as the only
system storage and similar special configurations) are just a bonus.
--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>
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