systemd is a system and service manager, replacement for SysVinit and Upstart. After a six months shift, during which it has been more granularly tested, Fedora 15 brings in, by default, a new system daemon whose code is designed from scratch, with the objective to take the maximum advantage offered by modern Linux kernel.
With systemd, Fedora 15 boots-up faster, particularly on SSD; native systemd service configuration files (or units) are much easier to understand and configure compared to sysvinit scripts, as systemd uses
.service files instead of bash script; all daemons are sorted into their own Linux cgroups, which you may explore beneath
/cgroup/systemd in the file system hierarchy; administrative features of the init system are considerably extended.
Refer to https://fedoraproject.org/wiki/Systemd for more complete information on systemd in Fedora.
== /run directory =-
Fedora 15 has a /run directory for storing runtime data. /run is now a tmpfs, and /var/run is bind mounted to it. /var/lock is bind mounted to /run/lock. Applications can use /run the same way as /var/run. Several programs including udev, dracut, mdadm, mount and initscripts used used hidden directories under /dev for runtime data during early bootup before /var is mounted. However /dev/ is supposed to be used for only device nodes and there is consensus between major distributions to shift to using /run instead. Fedora 15 is leading this change and the change including the benefits are explained in more detail here.
/var/run and /var/lock
/var/run and /var/lock are now bind mounted to /run and /run/lock from tmpfs, and hence emptied on reboot. Applications must ensure to recreate their own files/dirs on startup, and cannot rely that doing this at package installation will suffice. It is possible to use systemd's tmpfiles.d mechanism to recreate directories and files beneath /var/run and /var/lock on boot, if necessary. See tmpfiles.d(5) for details (http://0pointer.de/public/systemd-man/tmpfiles.d.html) and the conf files in /etc/tmpfiles.d for examples of such configuration. Fedora packaging guidelines for tmpfiles.d is at
4kB Sector disk boot support
Booting 4kB sector disks in UEFI environments is now supported.