Systemd – How to Create a New .slice File in Debian

cgroupdebiansystemd

I'm struggling to understand how to set up a new slice on my debian 10 system. I have created a file, system-db.slice by copying system.slice and changing a couple of things:

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=System DB Slice
Documentation=man:systemd.special(7)
DefaultDependencies=no
Before=slices.target
Requires=system.slice
After=system.slice

This doesn't appear to do anything at all; it doesn't show up in systemd-cgls, for example. On the other hand, systemctl finds it:

# systemctl status system-db.slice
● system-db.slice - System DB Slice
   Loaded: loaded (/etc/systemd/system/system-db.slice; static; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:systemd.special(7)

Clearly there are some things I haven't done or done wrong. How should I have done this? And where can I learn more about this?

Best Answer

The slice is only started when a service that uses the slice is started. You do not start it manually. Rather, you add Slice=my.slice to the unit that you want to be restricted by this slice.

Related Solutions

Systemd – How to Set Environment Variable in Service

Times change and so do best practices.

The current best way to do this is to run systemctl edit myservice, which will create an override file for you or let you edit an existing one.

In normal installations this will create a directory /etc/systemd/system/myservice.service.d, and inside that directory create a file whose name ends in .conf (typically, override.conf), and in this file you can add to or override any part of the unit shipped by the distribution.

For instance, in a file /etc/systemd/system/myservice.service.d/myenv.conf:

[Service]
Environment="SECRET=pGNqduRFkB4K9C2vijOmUDa2kPtUhArN"
Environment="ANOTHER_SECRET=JP8YLOc2bsNlrGuD6LVTq7L36obpjzxd"

Also note that if the directory exists and is empty, your service will be disabled! If you don't intend to put something in the directory, ensure that it does not exist.

For reference, the old way was:

The recommended way to do this is to create a file /etc/sysconfig/myservice which contains your variables, and then load them with EnvironmentFile.

For complete details, see Fedora's documentation on how to write a systemd script.

Find the location of a systemd unit file service

For units that are defined in actual, static files, this can be seen in systemctl status:

$ systemctl status halt-local.service
● halt-local.service - /usr/sbin/halt.local Compatibility
   Loaded: loaded (/lib/systemd/system/halt-local.service; static)
   Active: inactive (dead)

But there are units that are not defined by files, e.g. with systemd-cron installed. These have no useful location listed with status:

$ systemctl status cron-jojo-0.timer
● cron-jojo-0.timer - [Cron] "*/10 * * * * ..."
   Loaded: loaded (/var/spool/cron/crontabs/jojo)
   Active: active (waiting) since Mon 2015-05-18 14:53:01 UTC; 9min ago

In either case, though, the FragmentPath field is educating:

$ systemctl show -p FragmentPath cron-daily.service
FragmentPath=/lib/systemd/system/cron-daily.service
$ systemctl show -p FragmentPath cron-jojo-0.service
FragmentPath=/run/systemd/generator/cron-jojo-0.service
$ systemctl show -p FragmentPath halt-local.service
FragmentPath=/lib/systemd/system/halt-local.service

Best Answer

Related Solutions

Systemd – How to Set Environment Variable in Service

Find the location of a systemd unit file service

Related Topic