Systemd fails to start openvpn in lxd managed 16.04 container

I've been looking for a fix for this also. What I have found to work is to comment out the LimitNPROC line in /lib/systemd/system/[email protected].

Don't forget to run systemctl daemon-reload after that.

It's better to avoid modyfying systemd units originating from system packages. Just use systemd override drop-in:

systemctl edit openvpn@

Unit name for openvpn server might be different, eg. for package version 2.4.5-xenial0 it will be

systemctl edit openvpn-server@

Then put into editor:

[Service]
LimitNPROC=infinity

It should create /etc/systemd/system/[email protected]/override.conf file (or similar for corresponding unit name). To activate it you may want to reload systemd with

systemctl daemon-reload

If starting the unit is successful with LimitNPROC=infinity then go back and change the limit to a higher value than the default of 10. The limit is important to prevent the service from consuming all available pids which can cause a denial of service.

Credits:
override: https://unix.stackexchange.com/a/398541/218321
"unlimited limit": https://unix.stackexchange.com/a/345596/218321