data: Remove all /var/tmp/flatpak-cache-* directories on boot

[bertogg]

No one is clearing those directories so they pile up and can take a significant amount of disk space.

Resolves: #1119

[TingPing]

This looks correct to me. The cache is indeed only used for the lifetime of a users session.

I'll give a moment for any other maintainer to chime in also.

[JakobDev]

The cache is indeed only used for the lifetime of a users session.

If it's only for a user session, why is it in /var/tmp and not in /tmp?

[evelikov]

The cache is indeed only used for the lifetime of a users session.

If it's only for a user session, why is it in /var/tmp and not in /tmp?

AFAICT the existing code hard-codes the /var/tmp one - see

flatpak/common/flatpak-dir.c

Line 1953 in 14c5483

path = g_strdup ("/var/tmp/flatpak-cache-XXXXXX");

- and does not use /tmp.

[TingPing]

If it's only for a user session, why is it in /var/tmp and not in /tmp?

Well /tmp is a tmpfs, so not comparable, but it is stored in /var/tmp for system packages as its likely on the same filesystem as /var/lib/flatpak.

[bertogg]

If it's only for a user session, why is it in /var/tmp and not in /tmp?

Well /tmp is a tmpfs, so not comparable, but it is stored in /var/tmp for system packages as its likely on the same filesystem as /var/lib/flatpak.

Also it's my understanding that /tmp should not be used for large files.