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.
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.
This change is compliant with the Filesystem Hierarchy Standard, which allows distributions to create new directories in the root hierarchy as long as there is careful consideration of the consequences. Lennart Poettering has filed a request to update the FHS standard to include this change as well.
/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.