How to properly delete PHP sessions files to free inodes?

So this morning, I noticed I was having trouble using tab-completion while logged into ssh. I received a cannot create temp file for here-document: No space left on device message whenever I attempted a tab-completion.

Confused by the “no space left” message when I was using less than 30% of the disk space on the device, I dug into it a little deeper and realized the lack of available “inodes” was actually the problem.

I managed to clear enough files manually to run the following command: sudo find / -xdev -printf '%h\0' | sort -z | uniq -cz | sort -nrzk 1 | tr '\0' '\n' | head -n 50

That revealed the biggest culprit to be PHP and HHVM session files (FWIW, I don’t use HHVM anymore).

1261734 /var/lib/php5 543376 /var/lib/hhvm/sessions

I’d love to clear these out (especially the HHVM ones) but am not sure of the proper way to do it.

Any advice would be much appreciated.