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In Fedora 15 and above, /var/run and /var/lock are tmpfs filesystems. As such, they are created empty on every reboot. For files intended to be placed into those directories, this should normally not pose any problems. For directories, however, we often need to create the directories ahead of time. This is best done using the tmpfiles.d mechanism that both upstart and systemd share.
tmpfiles.d configuration
Example spec file
Why not create the directories with XXXXXX instead?
There are multiple ways to try creating the directories but most suffer some disadvantage that tmpfiles.d addresses:
Have the daemon create the directory when it starts up
Many times, daemons run as an unprivileged user who would not be allowed to create new directories directly into /var/run or /var/lock.
Have the init script create the directory when it starts up the daemon
Since the init script is run by root, before the daemon drops privileges, why not create the directories there?
- This code would need to be implemented in every init script packaged. Since both upstart and systemd support tmpfiles.d, we can cut down on the number of places we have to put code like this.
- Having to add the mkdir to the systemd unit files when tmpfiles.d is already in place introduces the need to run shell code for that init script. Systemd is no longer able to handle starting the daemon by itself which slows things down. The shell code also introduces imperative constructs into the otherwise declarative structure which is nice to avoid.
- Properly labelling the created directories is done automatically by the tmpfiles.d mechanism but would have to be manually done by the init script.