Consider to move global flock file location

[buhtz]

Describe the problem, feature or ask a question:

This is just a note about an issue that might become relevant in the future.

There is in ongoing discussion and conflict in context of systemd and Debian about world-writeable directories for flock files.

• https://lwn.net/Articles/1041316/
• https://lwn.net/Articles/1032947/
• https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch05s09.html
• debian#1110981: should not use /run/lock/ for private lock files
• debian#1115317: advice for using /var/lock (which is a link to /run/lock)

I need to do further research to decide about if this is a problem for BIT and how we handle that. One option would be to move the flock file somewhere to /tmp/*.

Problem: The current implementation in common/flock.py tries several locations for the flock file. In the final end it switches from a global (all-user) to a user-specific flock file. This happens without any entry to the syslog or other warnings.