systemd是一個init程序。根據之前 Upstart的一些介紹大家應該簡要了解了傳統Sysvinit系統的不足之處。不過，這次的systemd的設計思想更為超前，也可以說是借鑑了OSX上launchd的思路。
systemd 227 發布，此版本更新內容如下：
* systemd now depends on util-linux v2.27
* libmount mandates /etc/mtab not to be regular file, and
systemd now enforces this condition at early boot.
* Support for the "pids" cgroup controller has been added.
* Support for the "net_cls" cgroup controller has been added.
This adds a new config directive called NetClass= to CGroup
enabled units.
* 'systemctl is-system-running' now returns 'offline' if the
system is not booted with systemd.
* Watchdog timeouts have been increased to 3 minutes for all
in-tree service files.
* 'machine-id-commit' functionality has been merged into
'machine-id-setup --commit'.
* The WorkingDirectory= directive in unit files may now be set
to the special value '~'.
* "machinectl shell" will now open the shell in the home
directory of the selected user by default.
* The CrashChVT= configuration file setting is renamed to
CrashChangeVT=, following our usual logic of not
abbreviating unnecessarily.
* The PrivateTmp=, PrivateDevices=, PrivateNetwork=,
NoNewPrivileges=, TTYPath=, WorkingDirectory= and
RootDirectory= properties can now be set for transient
units.
* The systemd-analyze tool gained a new "set-log-target" verb
to change the logging target the system manager logs to
dynamically during runtime.
* In nspawn /sys is now mounted as tmpfs, with only a selected
set of subdirectories mounted in from the real sysfs.
* Support for USB FunctionFS activation has been added.
* The "systemctl exit" command now optionally takes an
additional parameter that sets the exit code to return from
the systemd manager when exiting.
* sd-bus gained the new API calls sd_bus_path_encode_many()
and sd_bus_path_decode_many() that allow easy encoding and
decoding of multiple identifier strings inside a D-Bus
object path.
* systemd-cgtop gained support for a -M/--machine= switch to
show the control groups within a certain container only.
* "systemctl kill" gained support for an optional --fail
switch.
* A new systemd.crash_reboot=1 kernel command line option has
been added that triggers a reboot after crashing.
* The RuntimeDirectory= setting now understands unit
specifiers like %i or %f.
* A new (still internal) libary API sd-ipv4acd has been added,
that implements address conflict detection for IPv4.
* File descriptors passed during socket activation may now be
named. A new API sd_listen_fds_with_names() is added to
access the names.
* systemd-networkd gained support for:
- Setting the IPv6 Router Advertisment settings via
IPv6AcceptRouterAdvertisements= in .network files.
- Configuring the HelloTimeSec=, MaxAgeSec= and
ForwardDelaySec= bridge parameters in .netdev files.
- Configuring PreferredSource= for static routes in
.network files.
* The "ask-password" framework used to query for LUKS harddisk
passwords or SSL passwords during boot gained support for
caching passwords in the kernel keyring, if it is
available.
* When downloading tar or raw images using "machinectl
pull-tar" or "machinectl pull-raw", a matching ".nspawn"
file is now also downloaded, if it is available and stored
next to the image file.
* Units of type ".socket" gained a new boolean setting
Writable= which is only useful in conjunction with
ListenSpecial=. If true, enables opening the specified
special file in O_RDWR mode rather than O_RDONLY mode.
* systemd-rfkill has been reworked to become a singleton
service that is activated through /dev/rfkill on each rfkill
state change and saves the settings to disk.
* The journal daemon gained support for vacuuming old journal
files controlled by the number of files that shall remain,
in addition to the already existing control by size and by
date.
* udev will now create /dev/disk/by-path links for ATA devices
on kernels where that is supported.
* Galician, Serbian, Turkish and Korean translations were added.
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