Fatal Error Unable to create lock file: Bad file descriptor (9)

503 error on user websites caused by CageFS

Check the logs

tail /var/log/apache2/stderr.log

Fri Apr 29 12:32:02 2022 (95855): Fatal Error Unable to create lock file: Bad file descriptor (9)

To fix the issue follow this guide: Apache: Fatal Error Unable to create lock file: Bad file descriptor (9)

Disable CsageFS for that user:

/usr/sbin/cagefsctl --disable $username

and enable it back:

/usr/sbin/cagefsctl --enable $username