Dbus change of location from system_bus_socket

[Simon McVittie]

On Wed, 23 May 2018 at 16:03:11 +0200, Lennart Poettering wrote:
> On systemd systems /var/run *must* be a symlink to /run, thus making
> both directories synonymous. This is explicitly documented, and if you
> don't have such a symlink in place you will encounter breakage all
> over the place.

This is also true on all Debian derivatives (whether they use systemd
or not) since around 2011, and is a design that I would strongly recommend
in all OS distributions that have a FHS-like filesystem layout. There is
no reason to make those directories distinct: it will only break things,
for no benefit.

The system dbus-daemon still canonically listens on
/var/run/dbus/system_bus_socket, and by default this is even true on
systemd systems. For example, Debian's /lib/systemd/system/dbus.socket
has ListenStream=/var/run/dbus/system_bus_socket. If the dbus package
in CentOS/RHEL listens on /run/dbus/system_bus_socket, that would have
to be a local change: please contact that distribution's support channels.

https://bugs.freedesktop.org/show_bug.cgi?id=101628 tracks our attempts to
change the upstream default system bus address from ${localstatedir}/run
(normally /var/run) to ${runstatedir} (often /run). Unfortunately,
some (IMO misguided) OS distributions have both /var/run and /run and
make them distinct (the only example I know of is Slackware). If you
maintain such a distribution, even if you do not use systemd, I would
strongly recommend the approach taken in Debian and Ubuntu (years before
we adopted systemd): /run should be a tmpfs, and /var/run should be a
symbolic link or a bind-mount to /run. See 2011-era Debian sysv-rc and
initscripts packages for the migration paths that we used back then.

    smcv