I got this issue on Debian sid right now.
I have this in my /etc/fstab:
tmpfs /tmp tmpfs defaults,noatime,mode=1777,nosuid 0 0
tmpfs /var/spool/rsyslog tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/spool/anacron tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/spool/mqueue tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/spool/mqueue-client tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/cache tmpfs defaults,noatime,nodiratime 0 0
tmpfs /var/cache/locate tmpfs defaults,noatime,nodiratime 0 0
tmpfs /var/cache/ntpsec tmpfs defaults,noatime,nodiratime 0 0
tmpfs /var/cache/apt-show-versions tmpfs defaults,noatime,nodiratime 0 0
tmpfs /var/tmp tmpfs defaults,noatime 0 0
dic 10 11:27:43 KITT (apachectl)[564309]: apache2.service: Failed to set up mount namespacing: /var/cache/apache2/mod_cache_disk: No such file or directory
dic 10 11:27:43 KITT (apachectl)[564309]: apache2.service: Failed at step NAMESPACE spawning /usr/sbin/apachectl: No such file or directory
The issue was fixed with:
mkdir -p /var/cache/apache2/mod_cache_disk
I have to see if the issue still persist at next reboot of the machine as I am mount the /var/cache folder with tmpfs