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Sven Eden 5 years ago
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systemd System and Service Manager
#systemd on
Lennart Poettering
Kay Sievers
...and many others
LGPLv2.1+ for all code
- except src/basic/MurmurHash2.c which is Public Domain
- except src/basic/siphash24.c which is CC0 Public Domain
- except src/journal/lookup3.c which is Public Domain
- except src/udev/* which is (currently still) GPLv2, GPLv2+
Linux kernel >= 3.11
Linux kernel >= 4.2 for unified cgroup hierarchy support
Kernel Config Options:
CONFIG_CGROUPS (it is OK to disable all controllers)
CONFIG_FHANDLE (libudev, mount and bind mount handling)
udev will fail to work with the legacy sysfs layout:
Legacy hotplug slows down the system and confuses udev:
Userspace firmware loading is not supported and should
be disabled in the kernel:
Some udev rules and virtualization detection relies on it:
Support for some SCSI devices serial number retrieval, to
create additional symlinks in /dev/disk/ and /dev/tape:
Required for PrivateNetwork and PrivateDevices in service units:
Note that systemd-localed.service and other systemd units use
PrivateNetwork and PrivateDevices so this is effectively required.
Optional but strongly recommended:
CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
Required for CPUShares= in resource control unit settings
Required for CPUQuota= in resource control unit settings
For systemd-bootchart, several proc debug interfaces are required:
For UEFI systems:
We recommend to turn off Real-Time group scheduling in the
kernel when using systemd. RT group scheduling effectively
makes RT scheduling unavailable for most userspace, since it
requires explicit assignment of RT budgets to each unit whose
processes making use of RT. As there's no sensible way to
assign these budgets automatically this cannot really be
fixed, and it's best to disable group scheduling hence.
Note that kernel auditing is broken when used with systemd's
container code. When using systemd in conjunction with
containers, please make sure to either turn off auditing at
runtime using the kernel command line option "audit=0", or
turn it off at kernel compile time using:
If systemd is compiled with libseccomp support on
architectures which do not use socketcall() and where seccomp
is supported (this effectively means x86-64 and ARM, but
excludes 32-bit x86!), then nspawn will now install a
work-around seccomp filter that makes containers boot even
with audit being enabled. This works correctly only on kernels
3.14 and newer though. TL;DR: turn audit off, still.
glibc >= 2.16
libmount >= 2.20 (from util-linux)
libseccomp >= 1.0.0 (optional)
libblkid >= 2.24 (from util-linux) (optional)
libkmod >= 15 (optional)
PAM >= 1.1.2 (optional)
libcryptsetup (optional)
libaudit (optional)
libacl (optional)
libselinux (optional)
liblzma (optional)
liblz4 >= 119 (optional)
libgcrypt (optional)
libqrencode (optional)
libmicrohttpd (optional)
libpython (optional)
libidn (optional)
elfutils >= 158 (optional)
make, gcc, and similar tools
During runtime, you need the following additional
util-linux >= v2.26 required
dbus >= 1.4.0 (strictly speaking optional, but recommended)
dracut (optional)
PolicyKit (optional)
When building from git, the following tools are needed:
python (optional)
python-lxml (optional, but required to build the indices)
sphinx (optional)
The build system is initialized with ./ A tar ball
can be created with:
git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
When systemd-hostnamed is used, it is strongly recommended to
install nss-myhostname to ensure that, in a world of
dynamically changing hostnames, the hostname stays resolvable
under all circumstances. In fact, systemd-hostnamed will warn
if nss-myhostname is not installed.
To build HTML documentation for python-systemd using sphinx,
please first install systemd (using 'make install'), and then
invoke sphinx-build with 'make sphinx-<target>', with <target>
being 'html' or 'latexpdf'. If using DESTDIR for installation,
pass the same DESTDIR to 'make sphinx-html' invocation.
Default udev rules use the following standard system group
names, which need to be resolvable by getgrnam() at any time,
even in the very early boot stages, where no other databases
and network are available:
audio, cdrom, dialout, disk, input, kmem, lp, tape, tty, video
During runtime, the journal daemon requires the
"systemd-journal" system group to exist. New journal files will
be readable by this group (but not writable), which may be used
to grant specific users read access. In addition, system
groups "wheel" and "adm" will be given read-only access to
journal files using systemd-tmpfiles.service.
The journal gateway daemon requires the
"systemd-journal-gateway" system user and group to
exist. During execution this network facing service will drop
privileges and assume this uid/gid for security reasons.
Similarly, the NTP daemon requires the "systemd-timesync" system
user and group to exist.
Similarly, the network management daemon requires the
"systemd-network" system user and group to exist.
Similarly, the name resolution daemon requires the
"systemd-resolve" system user and group to exist.
Similarly, the kdbus dbus1 proxy daemon requires the
"systemd-bus-proxy" system user and group to exist.
systemd ships with three NSS modules:
nss-myhostname resolves the local hostname to locally
configured IP addresses, as well as "localhost" to
nss-resolve enables DNS resolution via the systemd-resolved
DNS/LLMNR caching stub resolver "systemd-resolved".
nss-mymachines enables resolution of all local containers
registered with machined to their respective IP addresses.
To make use of these NSS modules, please add them to the
"hosts: " line in /etc/nsswitch.conf. The "resolve" module
should replace the glibc "dns" module in this file.
The three modules should be used in the following order:
hosts: files mymachines resolve myhostname
When calling "systemctl enable/disable/is-enabled" on a unit which is a
SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
this needs to translate the action into the distribution specific
mechanism such as chkconfig or update-rc.d. Packagers need to provide
this script if you need this functionality (you don't if you disabled
SysV init support).
Please see src/systemctl/systemd-sysv-install.SKELETON for how this
needs to look like, and provide an implementation at the marked places.
systemd will warn you during boot if /etc/mtab is not a
symlink to /proc/mounts. Please ensure that /etc/mtab is a
proper symlink.
systemd will warn you during boot if /usr is on a different
file system than /. While in systemd itself very little will
break if /usr is on a separate partition, many of its
dependencies very likely will break sooner or later in one
form or another. For example, udev rules tend to refer to
binaries in /usr, binaries that link to libraries in /usr or
binaries that refer to data files in /usr. Since these
breakages are not always directly visible, systemd will warn
about this, since this kind of file system setup is not really
supported anymore by the basic set of Linux OS components.
systemd requires that the /run mount point exists. systemd also
requires that /var/run is a symlink to /run.
For more information on this issue consult
To run systemd under valgrind, compile with VALGRIND defined
(e.g. ./configure CPPFLAGS='... -DVALGRIND=1'). Otherwise,
false positives will be triggered by code which violates
some rules but is actually safe.
Currently, systemd-timesyncd defaults to use the Google NTP
servers if not specified otherwise at configure time. You
really should not ship an OS or device with this default
setting. See DISTRO_PORTING for details.
Elogind User, Seat and Session Manager
Elogind is the systemd project's "logind", extracted out to be a
standalone daemon. It integrates with PAM to know the set of users
that are logged in to a system and whether they are logged in
graphically, on the console, or remotely. Elogind exposes this
information via the standard org.freedesktop.login1 D-Bus interface,
as well as through the file system using systemd's standard
/run/systemd layout. Elogind also provides "libelogind", which is a
subset of the facilities offered by "libsystemd". There is a
"libelogind.pc" pkg-config file as well.
All of the credit for elogind should go to the systemd developers.
For more on systemd, see All of the blame
should go to Andy Wingo, who extracted elogind from systemd.
Elogind was branched from systemd version 219, and preserves the git
history of the systemd project. The version of elogind is the
upstream systemd version, followed by the patchlevel of elogind. For
example version 219.12 is the twelfth elogind release, which aims to
provide a subset of the interfaces of systemd 219.
To contribute to elogind, fork the current source code from github:
Send a pull request for the changes you like.
To chat about elogind:
#guix on
Finally, bug reports:
Why bother?
Elogind has been developed for use in GuixSD, the OS distribution of
GNU Guix. See for more on Guix. GuixSD uses a
specific init manager (DMD), for reasons that are not relevant here,
but still aims to eventually be a full-featured distribution that can
run GNOME and other desktop environments. However, to run GNOME these
days means that you need to have support for the login1 D-Bus
interface, which is currently only provided by systemd. That is the
origin of this project: to take the excellent logind functionality
from systemd and provide it as a standalone package.
We like systemd. We realize that there are people out there that hate
it. You're welcome to use elogind for whatever purpose you like --
as-is, or as a jumping-off point for other things -- but please don't
use it as part of some anti-systemd vendetta. Systemd hackers are
smart folks that are trying to solve interesting problems on the free
desktop, and their large adoption is largely because they solve
problems that users and developers of user-focused applications care
about. We are appreciative of their logind effort and think that
everyone deserves to run it if they like, even if they use a different
PID 1.
Differences relative to systemd
The pkg-config file is called libelogind, not libsystemd or
The headers are in <elogind/...>, so like <elogind/sd-login.h> instead
of <systemd/sd-login.h>.
Libelogind just implements login-related functionality. It also
provides the sd-bus API.
Unlike systemd, whose logind arranges to run user sessions in cgroups
via RPC calls to systemd, in elogind there is no systemd so there are
no cgroups. This has a few implications:
* Elogind does not create "slices" for users. Elogind will not
record that users are associated with slices.
* Systemd's logind waits for all user jobs to stop before recording
that a user's session has gone away. Since we have no cgroups,
elogind just removes the session directly when
indicates the user has logged out.
* The /run/systemd/slices directory will always be empty.
* Support for lingering is not so great.
Elogind does not manage virtual terminals.
Elogind does monitor power button and the lid switch, like systemd,
but instead of doing RPC to systemd to suspend, poweroff, or restart
the machine, elogind just does this directly. For suspend, hibernate,
and hybrid-sleep, elogind uses the same code as systemd-sleep.
Instead of using a separate sleep.conf file to configure the sleep
behavior, this is included in the [Sleep] section of
/etc/elogind/login.conf. See the example login.conf for more. For
shutdown, reboot, and kexec, elogind shells out to "halt", "reboot",
and "kexec" binaries.
The loginctl command has the poweroff, reboot, sleep, hibernate, and
hybrid-sleep commands from systemd, as well as the --ignore-inhibitors
The PAM module is called, not
LGPLv2.1+ for all code
- except src/shared/MurmurHash2.c which is Public Domain
- except src/shared/siphash24.c which is CC0 Public Domain
- except src/journal/lookup3.c which is Public Domain
glibc >= 2.14
libmount >= 2.20 (from util-linux)
libseccomp >= 1.0.0 (optional)
libblkid >= 2.24 (from util-linux) (optional)
PAM >= 1.1.2 (optional)
libacl (optional)
libselinux (optional)
make, gcc, and similar tools
During runtime, you need the following additional dependencies:
dbus >= 1.4.0 (strictly speaking optional, but recommended)
PolicyKit (optional)
When building from git, you need the following additional
gtkdocize (optional)