Gentoo Configuration Guide: systemd
As of now, the Gentoo Handbook, which is the official Gentoo installation guide, mainly focuses on steps to install a system based on OpenRC instead of systemd. After all, as a project mainly maintained by Gentoo developers, it would be a surprise if Gentoo did not introduce OpenRC as the distribution’s init system with primary support. For people who want to use systemd on Gentoo, the Handbook does include some instructions in itself, but it sometimes asks the users to refer to the standalone systemd article too. In my opinion, that article is very comprehensive but is not well organized: steps that should be performed during the installation process scatter around the entire article, making it easy to miss required steps. Therefore, this article is created as my effort to come up with a clear and working procedure for getting systemd to work on Gentoo.
How to Interpret This Article’s Instructions
The general installation steps of Gentoo are the same regardless of which init system is used, but there are some details that would change with the choice of init system. Users who want to use systemd can follow all Handbook’s instructions to install the operating system, but when it comes to a step in the Handbook for which this article has extra comments, notes or remarks, please pay attention to the relevant information here.
Configuring the Kernel
Users who want to create their own kernel configuration should make sure all mandatory options required by systemd listed here are enabled.
For systemd, an initramfs is probably needed to ensure that /usr is mounted
at boot time. More related information can be found here.
Note that if a distribution kernel package is used, there is no
need to worry about this matter because all distribution kernel packages build
and use an initramfs by default.
Configuring the System
Host and Domain Information
If the Handbook’s instruction says that the hostnamectl command should be
used, do not follow it. Instead, set the hostname later when the
systemd-firstboot command is being run (which is mentioned at the bottom of
the Configuring the system chapter).
This is because in the chroot environment, hostnamectl attempts to change the
hostname for the running host system (e.g. the livecd system if the minimal
installation CD or the LiveGUI image is used) rather than the new system that
is chrooted into. If the host system uses systemd, then its hostname will be
subtlely altered in this way. If it uses OpenRC (which is true for the minimal
installation CD and the LiveGUI image), hostnamectl will exit with an error.
Network
systemd has a component called systemd-networkd that already provides network
interface management capabilities – including DHCP, so users can elect to use
it directly without installing any other packages. To use systemd-networkd,
please ignore all related Handbook instructions and peruse the information
given here.
Installing Tools
Cron Daemon
Although systemd supports timer units, which can replace cron daemons, some
Gentoo packages will still install cron scripts into directories like
/etc/cron.{daily,hourly} for tasks they need to run every day or every hour
respectively, even if systemd is installed on the system and the systemd USE
flag is enabled.
For example, below is a list of scripts installed into /etc/cron.daily on my
system, which runs systemd:
leo@nvme-fussy ~ $ ls /etc/cron.daily/
logrotate man-db mlocate suse.de-snapper
While those packages are shipped with one or more corresponding systemd timer units, they are disabled by default, so users must manually enable them, which is something they might forget to do.
Therefore, the easiest way to ensure that all scheduled tasks can run as
intended is to install a cron daemon, even if systemd is used. The cron daemon
runs every script under a /etc/cron.* directory at regular intervals, so as
long as a package installs its cron script to one of the /etc/cron.*
directories, which most Gentoo packages that contain a scheduled task do, it
will be picked up and handled by the cron daemon without any extra user
intervention required. There would be no more hassle of manually finding and
enabling systemd timer units for newly-installed packages.
At this point, the Handbook draws readers’ attention to sys-process/cronie.
Cronie should work fine on systemd; however, there exists
sys-process/systemd-cron, a package that integrates those cron scripts under
/etc/cron.* directories with systemd better and more tightly. systemd-cron
is not a standalone cron daemon like Cronie; rather, it is mainly just a set of
systemd timer units that can run all scripts under /etc/cron.* directories at
appropriate times.
Users who wish to install a cron daemon on systemd and use
sys-process/systemd-cron as the cron daemon can refer to information over
here.
Installing a DHCP Client
If systemd-networkd has been chosen for network interface management, then
because it already has a built-in DHCP client, it is not necessary to install a
standalone one.
Remarks to the systemd Article on Gentoo Wiki
Those should be all the instructions users need to properly configure systemd on Gentoo. The systemd article on Gentoo Wiki contains some additional useful information pertaining to systemd configuration, and systemd users are suggested to use it as a reference. There are a few additional notes for information in that article.
/etc/mtab
The systemd article says /etc/mtab should be a symbolic link to
/proc/self/mounts, but chances are this link has already been created in the
stage3 archive the user has downloaded. To check it, please run:
$ ls -l /etc/mtab
If something like the following is shown, then the link has been established correctly, and there is no need to create it again:
lrwxrwxrwx 1 root root 17 Nov 18 23:41 /etc/mtab -> /proc/self/mounts