50

Sometimes these things can be hard for first-timers. Being a do-it-myself person, I read that there are two folders for unit files (not in user mode).

/usr/lib/systemd/system/: units provided by installed packages
/etc/systemd/system/: units installed by the system administrator

Conflicting with this understanding is the following answer: https://unix.stackexchange.com/a/47715/33386. Can someone fill in the missing information so that I understand what is going on? (UPDATE: The answer has been updated, and my understanding no longer conflicts with it.)

Also, it seems that the scripts are organized in subfolders within the /etc/systemd/system/ folder:

getty.target.wants
multi-user.target.wants

In another location I read that there are other locations. It seems these are for user-specific services.

/usr/lib/systemd/user/ where services provided by installed packages go.
/etc/systemd/user/ where system-wide user services are placed by the system administrator.
~/.config/systemd/user/ where the user puts its own services.

Update 2015-08-31:

For the sake of others, here is a link to a related question I recently asked: Is there a designated place for scripts that are (indirectly) automatically executed by systemd?

  • 4
    /etc/systemd/system is where you put your scripts, pacman puts package scripts in /usr/lib/systemd/system and issuing systemctl enable foo.service creates symlinks from /usr to /etc... – jasonwryan Aug 23 '15 at 20:42
  • 1
    See man systemd.target: it explains the reasoning behind the groupings. – jasonwryan Aug 31 '15 at 7:46
49

The best place to put system unit files: /etc/systemd/system Just be sure to add a target under the [Install] section, read "How does it know?" for details. UPDATE: /usr/local/lib/systemd/system is another option, read "Gray Area" for details."

The best place to put user unit files: /etc/systemd/user or $HOME/.config/systemd/user but it depends on permissions and the situation.

The truth is that systemd units (or as the intro sentence calls them, "unit configurations") can go anywhere—provided you are willing to make manual symlinks and you are aware of the caveats. It makes life easier to put the unit where systemctl daemon-reload can find it for some good reasons:

  • Using a standard location means that systemd generators will find them and make them easy to enable at boot with systemctl enable. This is because your unit will automatically be added to a unit dependency tree (a unit cache).
  • You do not need to think about permissions, because only the right privileged users can write to the designated areas.

How does it know?

And how exactly does systemctl enable know where to create the symlink? You hard code it within the unit itself under the [install] section. Usually there is a line like

[Install]
WantedBy = multi-user.target

that corresponds to a predefined place on the filesystem. This way, systemctl knows that this unit is dependent on a group of unit files called multi-user.target ("target" is the term used to designate unit dependency groups. You can list all groups with systemctl list-units --type target). The group of unit files to be loaded with a target is put in a targetname.target.wants directory. This is just a directory full of symlinks (or the real thing). If your [Install] section says it is WantedBy the multi-user.target, but if a symlink to it does not exist in the multi-user.target.wants directory, then it will not load. When the systemd unit generators add your unit file to the dependency tree cache at boot (you can manually trigger generators with systemctl daemon-reload), it automatically knows where to put the symlink—in this case in the directory /etc/systemd/system/multi-user.target.wants/ should you enable it.

Key Points in the Manual:

Additional units might be loaded into systemd ("linked") from directories not on the unit load path. See the link command for systemctl(1).

Under systemctl, look for Unit File Commands

Unit File Load Path

Unit files are loaded from a set of paths determined during compilation, described in the two tables below. Unit files found in directories listed earlier override files with the same name in directories lower in the list.

When the variable $SYSTEMD_UNIT_PATH is set, the contents of this variable overrides the unit load path. If $SYSTEMD_UNIT_PATH ends with an empty component (":"), the usual unit load path will be appended to the contents of the variable.

Table 1 and Table 2 from man systemd.unit are good.

Load paths when running in system mode (--system).

  • /etc/systemd/system Local configuration
  • /run/systemd/system Runtime units
  • /usr/lib/systemd/system Units of installed packages

Load path when running in user mode (--user)

  • $XDG_CONFIG_HOME/systemd/user User configuration (only used when $XDG_CONFIG_HOME is set)
  • $HOME/.config/systemd/user User configuration (only used when $XDG_CONFIG_HOME is not set)
  • /etc/systemd/user Local configuration
  • $XDG_RUNTIME_DIR/systemd/user Runtime units (only used when $XDG_RUNTIME_DIR is set)
  • /run/systemd/user Runtime units
  • $XDG_DATA_HOME/systemd/user Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is set)
  • $HOME/.local/share/systemd/user Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is not set)
  • /usr/lib/systemd/user Units of packages that have been installed system-wide

Gray Area

On the one hand, the File Hierarchy Standard specifies that /etc is for local configurations that do not execute binaries. On the other hand it specifies that /usr/local/ "is for use by the system administrator when installing software locally". You could also argue (if not just for the purpose of organization) that all system unit files should go under /usr/local/lib/systemd/system, but this is intended for unit files that are part of "software" not from a package manager. The corresponding systemd user units that are system-wide could go under /usr/local/lib/systemd/user.

  • The advice about putting unit files in /etc/systemd/system, is that general advice for self created unit files? Anything installed by a package manager should always put them in /usr/lib/systemd/system for eg. – slm Aug 6 '18 at 20:25
  • @slm Yes, when the question refers to my systemd unit files, it is intended to imply self-created ones. – Jonathan Komar Sep 6 '18 at 19:44
  • I would distinct: /etc/systemd/user for (guaranteed) system wide user services and ~/.config/systemd/user for custom user specific services. – Suuuehgi May 17 at 21:26
16

/etc/systemd/system is where you put your scripts, pacman puts package scripts in /usr/lib/systemd/system.

Issuing systemctl enable foo.service creates symlinks from /usr to /etc. See the Unit Load Path section of man systemd.unit(5) for more detail.

  • @macmadness86 it's missing because it it unrelated to the question. – jasonwryan May 25 '17 at 6:43
1

I've written 3, one for ntpd, one for a second, static ethernet card, and one for running p0f, the passive OS identifer. I put them all in /etc/systemd/system. Looks like I could maybe let systemd handle the NTP stuff, but I don't think I want to rely on it that much.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.