PHP-FPM security setting "PrivateTmp=true" writes PHP session files to /tmp instead of session.save_path

Symptoms

All inodes are used in /tmp when PHP-FPM is used.

Description 

When a /tmp partition is smaller in size the inode count has the potential of being reached when PHP-FPM is used. On a CentOS server systemd enables PrivateTmp with "PrivateTmp=true" and forces the files to be written into /tmp

Workaround

The workaround here is to put a root cron job in place to remove sess_* files older than 1 day. This cron job should be run at the end of the day at 11 PM instead of 1 AM as that will just leave one hour of sess_ files in place. The command to add to root's crontab is:

find /tmp/systemd-private*php-fpm.service* -name sess_* ! -mtime -1 -exec rm -f '{}' \;

This command will remove sess_* files older than one day. This can be changed with the mtime variable. The above has -1 one but you can change this to -3 for 3 days instead.