Systemd

systemd is a modern sysvinit & RC replacement for Linux systems. It is supported in Gentoo as an alternate init system.

Kernel
systemd makes use of many modern Linux kernel features. Right now, the lower bound on kernel version is set in the ebuild to 2.6.39. In addition to that, the following kernel configuration options are required:

For UEFI system you'll also need to enable the following:

In the case you are using BFQ scheduler, it's recommended by BFQ upstream to enable "BFQ hierarchical scheduling support" under "Enable the block layer -> IO Schedulers"

The directory
The directory is used by systemd and other applications as a non-persistent storage for runtime data like pid files, sockets and state files.

The systemd package will create directory itself. However, please note that this change will trigger automatic mounting of it in OpenRC as well, and may trigger using it by different software packages.

Upstream only supports file being a symlink to. Also not creating this symlink will cause problems with mount and df. In the past some utilities wrote information (like mount options) into and thus it was supposed to be file. Currently all software (but nfs ) is supposed to avoid this problem but before you do switch check to be sure that you are not affected by any regressions.

To create the symlink, run:

Ensure /usr is present at boot time
For a split /usr configuration, one must use an initramfs to mount /usr before starting systemd. See the Official Initramfs Gentoo Guide for instructions.

Using LVM2 with Initramfs
In the case you are using sys-fs/lvm2 and booting with an initramfs, you will need to generate it using and running:

Installation
and have a circular dependency which necessitates a 2-stage installation.


 * 1) Install sys-apps/dbus with USE="-systemd". This is probably already done if you have a working desktop environment.
 * 2) Enable the systemd USE flag globally (make.conf) and install sys-apps/systemd. This may also be accomplished by a world update.

The consolekit use flag should also be disabled to prevent conflicts with the systemd-logind service.

Booting with systemd
In order to run systemd, you have to switch the init that your executable kernel (or your initramfs) uses.

Grub Legacy (0.x)
The init=/usr/lib/systemd/systemd argument should be added to the kernel command-line. An example excerpt from would look like:

Should the system boot using openrc, try using real_init instead of init

Grub 2
If using the grub2-mkconfig configuration generator, add the init option to GRUB_CMDLINE_LINUX.

If writing a configuration by hand (experts only), append the init parameter to the linux or linux16 command.

In kernel config
You can also set this in your kernel configuration. See "Processor type and features" -> "Built-in kernel command line". Note that this technique works for both grub and grub2.

Post Installation Configuration
systemd supports a few system configuration files to set the most basic system details. If you decide to set this configurations before rebooting using systemd, you will need to launch the following for being able to use some of the referred tools:

Hostname
A tool called hostnamectl exists for editing and. To change hostname, run:

Refer to man hostnamectl for more options.

Locale
Usually, you will get your locale properly migrated from openRC when installing systemd. If you still want to configure it, the tool localectl is used to set locale and console or X11 keymaps. To change the system locale, run the following command.

To change the virtual console keymap:

And finaly, to set the X11 layout:

If needed you can specify the model, variant and options too:

Time & Date
Time and date can be set using the timedatectl utility.

Automatic module loading
Automatic module loading is configured in a different file, or rather directory of files. The configuration files are stored in /etc/modules-load.d. On boot every file with a list of modules will be loaded. The file format is a list of modules seperated by newline and can have any name you want as long as it ends with .conf. You can seperate out the module loading by program, service or whatever way you like. My virtualbox.conf example is listed below. But I can image one also has an iptables.conf for all the kernel modules needed for your firewall or one big file with all modules.

Handling of log files
Systemd has its own way of handling log files without needing to rely on any external log system (like syslog-ng or rsyslog). Anyway, you can still configure it to use your preferred external tool for handling them. Please type man journald.conf for learning about how to configure journald to suit your needs.

/tmp is now in tmpfs
Unless you explicitly mount some other filesystem to /tmp in your fstab, systemd will mount /tmp as tmpfs. That means it will be emptied on every boot and its size will be limited to 50% of your RAM size. To know why this is the desired behavior and how to modify it, take a look to API File Systems

Configure verbosity of boot process
When migrating to systemd you will probably notice differences regarding verbosity of boot process:
 * quiet option not only affects to kernel output, but also to systemd itself. Then, while you are setting up systemd for your machine, you will probably want to drop it to see any errors could arise more easily. After that, you can add it back to get a quiet (and faster) boot.
 * Even passing quiet option, you can still configure systemd to show its status by also passing systemd.show_status=1.
 * When not using quiet option, you could get some messages overwriting consoles, that is caused by kernel configuration (see man 5 proc and look for /proc/sys/kernel/printk). To tweak it you can pass the loglevel=5 boot parameter to the kernel (or a lower value like 1).

Services
At some point you will have to reboot your system in order to get systemd running (in system mode). Be sure to read all of this document to ensure you have systemd configured as completely as possible before rebooting. Note that journalctl(8) works with systemd(8) not running, but that systemctl(8) will not do anything useful without systemd running. You will likely want to complete the service configuration (enabling and starting of services) after you get logged in to your system running systemd.

OpenRC services
Although systemd originally intended to support running old init.d scripts, that support is not suited well for a dependency-based RC like OpenRC and thus is completely disabled on Gentoo. OpenRC provides additional measures to ensure that init.d scripts can't be run when OpenRC was not used to boot the system (otherwise the results would be unpredictable).

Listing available services
All global service files are installed in. Thus, the simplest way of looking up available service units is listing that directory:

The following file suffixes are of interest:
 * - plain service files (e.g. ones just running a daemon directly),
 * - socket listeners (much like inetd),
 * - filesystem triggers for services (running services when files change etc.).

Alternatively, systemctl tool can be used to list all services (including implicit ones):

And finally the systemadm graphical tool can be used. It can be installed with the package.

Installing custom service files
Any custom service files should be copied to the directory. The directory is reserved for service files installed by ebuilds.

Enabling and disabling services
The usual way of enabling a service is using

Services can be disabled likewise:

These commands enable services using their default name in default target (both specified in Install section of the service file). However, sometimes services either don't provide that information or you want to use another name/target.

Enabling a service under a custom name
This is especially a case for template services -- services in which part of the name following @ (at sign) is used as a parameter to the service. This is often used to specify the terminal on which getty will run.

To enable a service under custom name, you have to create a symlink to the service file in correct directory. The name of that directory can either specify a target or another service which will depend on the new one.

For example, to enable stand-alone wpa_supplicant on wlan0, type:

To disable the service, just remove the symlink:

Native services
Some of Gentoo packages already install systemd unit files. For these services, it is enough to enable them. A quick summary of packages installing unit files can be seen on systemd eclass users list.

The following table lists systemd services matching OpenRC ones:

Troubleshooting

 * Upstream debugging guide
 * Upstream debugging guide
 * Upstream debugging guide

systemd-logind & pam_systemd
systemd intends to provide an integrated ConsoleKit replacement called logind. Some applications (like NetworkManager and polkit) provide support for it through USE=systemd. Please note that this flag usually disables ConsoleKit support as well and thus packages may stop working as expected if the procedure described below is not fulfilled. If you're having issues with not being able to detect NetworkManager is running, modify your system-auth file to add pam_systemd.

In order to enable session tracking for systemd-logind, you have to enable the pam_systemd PAM module first. This can be done using USE=systemd on.

Except for tracking user logins (like ConsoleKit does), this will cause all user processes to belong to a cgroup. You can add controllers=... to provide additional cgroup controllers (like cpu for CPU load balancing). You can also add kill-session-processes=1 to ensure that all processes spawned by user are killed on logout. For more information, take a look at pam_systemd man page.

syslog-ng
Systemd creates as datagram socket   so you will need to tell syslog-ng to read from a unix-dgram instead of a unix-stream:

should be replaced with: in order to use the syslog-ng service in systemd.

sys-fs/cryptsetup
Systemd doesn't seem to respect ( ?):

Check for units that failed to start
To check for units that failed to start you can run:

Enable Debug Mode
To get more informations you need to set the following in :

sys-fs/udev
Systemd contains a version of udev so you can safely remove the sys-fs/udev und just keep the virtual virtual/udev.

sys-kernel/genkernel
sys-kernel/genkernel has been replaced by sys-kernel/genkernel-next. You should use it with the "--udev" option, lest you run into strange errors while using "lvcreate" as described here: https://bugs.gentoo.org/show_bug.cgi?id=480066#c19.

However, it might be that the generated initramfs still uses openrc instead of Systemd. In that case it is recommended to create an initramfs with sys-kernel/dracut.

e4rat usage
Please remember to edit /etc/e4rat.conf setting 'init' to /usr/lib/systemd/systemd, otherwise it will keep booting openrc.

External resources

 * FAQ
 * Tips and tricks