this issue started when we upgraded an lxc to buster.
solution was to set nesting option for the lxc.
Code:
systemctl status apache2.service
● apache2.service - The Apache HTTP Server
Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Sun 2019-08-11 09:52:05 EDT; 9ms ago
Docs: https://httpd.apache.org/docs/2.4/
Process: 32501 ExecStart=/usr/sbin/apachectl start (code=exited, status=226/NAMESPACE)
Aug 11 09:52:05 backuppc systemd[1]: Starting The Apache HTTP Server...
Aug 11 09:52:05 backuppc systemd[32501]: apache2.service: Failed to set up mount namespacing: Permission denied
Aug 11 09:52:05 backuppc systemd[32501]: apache2.service: Failed at step NAMESPACE spawning /usr/sbin/apachectl: Permission denied
Aug 11 09:52:05 backuppc systemd[1]: apache2.service: Control process exited, code=exited, status=226/NAMESPACE
Aug 11 09:52:05 backuppc systemd[1]: apache2.service: Failed with result 'exit-code'.
Aug 11 09:52:05 backuppc systemd[1]: Failed to start The Apache HTTP Server.
solution was to set nesting option for the lxc.