systemd is a modern sysvinit & RC replacement for Linux systems.
It is supported in Gentoo as an alternate init system. systemd
makes use of many modern Linux kernel features. Right now, the
lower bound on kernel version is set in the ebuild to 2.6.38. In
addition to that, the following kernel configuration options
should be enabled: The /run directory is used by systemd (and
some applications) as a non-persistent storage for runtime data
like pidfiles, sockets and state files. The systemd ebuild will
create /run 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 suggests that the /etc/mtab file should be a symlink to
/proc/self/mounts. This is not obligatory and can create
problems with mount -o user and NFS mounts. To create the
symlink: Often systemd guides mention creating the file
/etc/machine-id as a global replacement for the D-Bus specific
/var/lib/dbus/machine-id. In Gentoo