The unit files have no installation config (WantedBy, RequiredBy, Also, Aliassettings in the [Install] section, and DefaultInstance for template units).This means they are not meant to be enabled using systemctl.Possible reasons for having this kind of un

The unit files have no installation config (WantedBy, RequiredBy, Also, Alias
settings in the [Install] section, and DefaultInstance for template units).
This means they are not meant to be enabled using systemctl.
Possible reasons for having this kind of units are:

1) A unit may be statically enabled by being symlinked from another unit's
   .wants/ or .requires/ directory.
2) A unit's purpose may be to act as a helper for some other unit which has
   a requirement dependency on it.
3) A unit may be started when needed via activation (socket, path, timer,
   D-Bus, udev, scripted systemctl call, ...).
4) In case of template units, the unit is meant to be enabled with some
   instance name specified.

systemctl enable rc-local 활성화 하려는데 위와 같이 에러가 발생 한다.

해결 방법은

# vi /lib/systemd/system/rc-local.service

들어가서

맨밑에

[Install]
WantedBy=multi-user.target

추가 하면 된다.

# systemctl enable rc-local
Created symlink /etc/systemd/system/multi-user.target.wants/rc-local.service → /usr/lib/systemd/system/rc-local.service.

그럼 정상적으로 활성화가 된다.