The snapshot plugin works fine. Snapshots can be made

The snapshot plugin works fine. Snapshots can be made and restored.
However it indicates an error in:
Settings -> Server Info

Snapshot uses _SESSIONS to store temporary information about database tables and files during the backup and restore processing. Sessions are a default part of PHP.
Session save path: /var/lib/php5
Session save path is not a valid directory.
Session save path is not writeable.

I am unable to solve this, as I can not adjust the php.ini on this hosting service. Adding a directory on my highest level /var/lib/php5 also does not solve it.

First: Do I need to solve it? (everything seems to work fine)
Second: If it needs to be resolved, how do I go about it?

Thanks, Ben