[systemd-devel] Trivial denial of service using link to NFS mounted directory

[Andrey Borzenkov]

If symlink points to NFS (hard) mounted directory and NFS server is
down, running "sysyemctl list-unit-files" result in systemd hanging and
no more responding to anything. No way to switch vt (which is spawned
on demand), no way to reboot system, nothing. Killing systemctl itself
does not help, as it is systemd which crawls directories, not systemctl
in this case.

Apparently any other operation which requires systemd to access unit
file would give the same result.

Having (part of) filesystem on NFS is not that unrealistic, so it can
happen even unintentionally.