1 systemd System and Service Manager
7 git@github.com:systemd/systemd.git
8 https://github.com/systemd/systemd
11 https://lists.freedesktop.org/mailman/listinfo/systemd-devel
14 #systemd on irc.libera.chat
17 https://github.com/systemd/systemd/issues
20 https://0pointer.de/blog/projects/systemd.html
21 https://www.freedesktop.org/wiki/Software/systemd
29 LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
33 ≥ 4.3 for ambient capabilities
34 ≥ 4.5 for pids controller in cgroup v2
35 ≥ 4.6 for cgroup namespaces
36 ≥ 4.9 for RENAME_NOREPLACE support in vfat
37 ≥ 4.10 for cgroup-bpf egress and ingress hooks
38 ≥ 4.15 for cgroup-bpf device hook and cpu controller in cgroup v2
39 ≥ 4.17 for cgroup-bpf socket address hooks
40 ≥ 4.20 for PSI (used by systemd-oomd)
41 ≥ 5.3 for bounded loops in BPF program
42 ≥ 5.4 for signed Verity images
43 ≥ 5.7 for BPF links and the BPF LSM hook
45 ⛔ Kernel versions below 3.15 ("minimum baseline") are not supported at
46 all, and are missing required functionality (e.g. CLOCK_BOOTTIME
47 support for timerfd_create()).
49 ⚠️ Kernel versions below 4.15 ("recommended baseline") have significant
50 gaps in functionality and are not recommended for use with this version
51 of systemd (e.g. lack sufficiently comprehensive and working cgroupv2
52 support). Taint flag 'old-kernel' will be set. systemd will most likely
53 still function, but upstream support and testing are limited.
55 Kernel Config Options:
57 CONFIG_CGROUPS (it is OK to disable all controllers)
62 CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
65 CONFIG_FHANDLE (libudev, mount and bind mount handling)
67 udev will fail to work with the legacy sysfs layout:
68 CONFIG_SYSFS_DEPRECATED=n
70 Legacy hotplug slows down the system and confuses udev:
71 CONFIG_UEVENT_HELPER_PATH=""
73 Userspace firmware loading is not supported and should be disabled in
75 CONFIG_FW_LOADER_USER_HELPER=n
77 Some udev rules and virtualization detection relies on it:
80 Support for some SCSI devices serial number retrieval, to create
81 additional symlinks in /dev/disk/ and /dev/tape:
84 Required for PrivateNetwork= in service units:
86 Note that systemd-localed.service and other systemd units use
87 PrivateNetwork so this is effectively required.
89 Required for PrivateUsers= in service units:
92 Optional but strongly recommended:
96 CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
98 CONFIG_SECCOMP_FILTER (required for seccomp support)
99 CONFIG_KCMP (for the kcmp() syscall, used to be under
100 CONFIG_CHECKPOINT_RESTORE before ~5.12)
102 Required for CPUShares= in resource control unit settings:
104 CONFIG_FAIR_GROUP_SCHED
106 Required for CPUQuota= in resource control unit settings:
109 Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
110 IPEgressFilterPath= in resource control unit settings unit settings:
117 Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
118 resource control unit settings:
129 Required for signed Verity images support:
130 CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
131 Required to verify signed Verity images using keys enrolled in the MoK
132 (Machine-Owner Key) keyring:
133 CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING
134 CONFIG_IMA_ARCH_POLICY
135 CONFIG_INTEGRITY_MACHINE_KEYRING
137 Required for RestrictFileSystems= in service units:
141 CONFIG_DEBUG_INFO_BTF
142 CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
144 We recommend to turn off Real-Time group scheduling in the kernel when
145 using systemd. RT group scheduling effectively makes RT scheduling
146 unavailable for most userspace, since it requires explicit assignment of
147 RT budgets to each unit whose processes making use of RT. As there's no
148 sensible way to assign these budgets automatically this cannot really be
149 fixed, and it's best to disable group scheduling hence:
150 CONFIG_RT_GROUP_SCHED=n
152 It's a good idea to disable the implicit creation of networking bonding
153 devices by the kernel networking bonding module, so that the
154 automatically created "bond0" interface doesn't conflict with any such
155 device created by systemd-networkd (or other tools). Ideally there would
156 be a kernel compile-time option for this, but there currently isn't. The
157 next best thing is to make this change through a modprobe.d drop-in.
158 This is shipped by default, see modprobe.d/systemd.conf.
160 Required for systemd-nspawn:
161 CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
163 Required for systemd-oomd:
166 Note that kernel auditing is broken when used with systemd's container
167 code. When using systemd in conjunction with containers, please make
168 sure to either turn off auditing at runtime using the kernel command
169 line option "audit=0", or turn it off at kernel compile time using:
172 If systemd is compiled with libseccomp support on architectures which do
173 not use socketcall() and where seccomp is supported (this effectively
174 means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now
175 install a work-around seccomp filter that makes containers boot even
176 with audit being enabled. This works correctly only on kernels 3.14 and
177 newer though. TL;DR: turn audit off, still.
181 libmount >= 2.30 (from util-linux)
182 (util-linux *must* be built without --enable-libmount-support-mtab)
183 libseccomp >= 2.3.1 (optional)
184 libblkid >= 2.24 (from util-linux) (optional)
185 libkmod >= 15 (optional)
186 PAM >= 1.1.2 (optional)
187 libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
190 libbpf >= 0.1.0 (optional)
191 libfdisk >= 2.32 (from util-linux) (optional)
192 libselinux (optional)
194 liblz4 >= 1.3.0 / 130 (optional)
195 libzstd >= 1.4.0 (optional)
197 libqrencode (optional)
198 libmicrohttpd (optional)
199 libidn2 or libidn (optional)
200 gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
201 openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
202 elfutils >= 158 (optional)
204 tzdata >= 2014f (optional)
207 docbook-xsl (optional, required for documentation)
208 xsltproc (optional, required for documentation)
209 python >= 3.7 (required by meson too, >= 3.9 is required for ukify)
211 python-pefile (optional, required for ukify)
212 python-lxml (optional, required to build the indices)
213 pyelftools (optional, required for systemd-boot)
217 awk, sed, grep, and similar tools
218 clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
219 from source code in C)
221 During runtime, you need the following additional
224 util-linux >= v2.27.1 required (including but not limited to: mount,
225 umount, swapon, swapoff, sulogin,
227 dbus >= 1.4.0 (strictly speaking optional, but recommended)
228 NOTE: If using dbus < 1.9.18, you should override the default
229 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
233 To build in directory build/:
234 meson setup build/ && ninja -C build/
236 Any configuration options can be specified as -Darg=value... arguments
237 to meson. After the build directory is initially configured, meson will
238 refuse to run again, and options must be changed with:
239 meson configure -Darg=value build/
240 meson configure without any arguments will print out available options and
241 their current values.
244 ninja -C build -v some/target
246 sudo meson install -C build/ --no-rebuild
247 DESTDIR=... meson install -C build/
249 A tarball can be created with:
250 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
252 When systemd-hostnamed is used, it is strongly recommended to install
253 nss-myhostname to ensure that, in a world of dynamically changing
254 hostnames, the hostname stays resolvable under all circumstances. In
255 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
257 nss-systemd must be enabled on systemd systems, as that's required for
258 DynamicUser= to work. Note that we ship services out-of-the-box that
259 make use of DynamicUser= now, hence enabling nss-systemd is not
262 Note that the build prefix for systemd must be /usr/. (Moreover, packages
263 systemd relies on — such as D-Bus — really should use the same prefix,
264 otherwise you are on your own.) Split-usr and unmerged-usr systems are no
265 longer supported, and moving everything under /usr/ is required. Systems
266 with a separate /usr/ partition must mount it before transitioning into it
267 (i.e.: from the initrd). For more information see:
268 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
269 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
271 Additional packages are necessary to run some tests:
272 - nc (used by test/TEST-12-ISSUE-3171)
273 - python (test-udev which is installed is in python)
275 - python-evdev (used by hwdb parsing tests)
276 - strace (used by test/test-functions)
277 - capsh (optional, used by test-execute)
279 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
280 systemd main branch and latest major or stable releases are generally
281 expected to compile on current versions of popular distributions (at
282 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
283 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
284 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
285 attempt to support also other non-EOL versions of various distros.
286 Features which would break compilation on slightly older distributions
287 will only be introduced if there are significant reasons for this
288 (i.e. supporting them interferes with development or requires too many
289 resources to support). In some cases backports of specific libraries or
290 tools might be required.
292 The policy is similar for architecture support. systemd is regularly
293 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
294 and s390x), but should compile and work also on other architectures, for
295 which support has been added. systemd will emit warnings when
296 architecture-specific constants are not defined.
298 STATIC COMPILATION AND "STANDALONE" BINARIES:
299 systemd provides a public shared libraries libsystemd.so and
300 libudev.so. The latter is deprecated, and the sd-device APIs in
301 libsystemd should be used instead for new code. In addition, systemd is
302 built with a private shared library, libsystemd-shared-<suffix>.so,
303 that also includes the libsystemd code, and by default most systemd
304 binaries are linked to it. Using shared libraries saves disk space and
305 memory at runtime, because only one copy of the code is needed.
307 It is possible to build static versions of systemd public shared
308 libraries (via the configuration options '-Dstatic-libsystemd' and
309 '-Dstatic-libudev'). This allows the libsystemd and libudev code to be
310 linked statically into programs. Note that mixing & matching different
311 versions of libsystemd and systemd is generally not recommended, since
312 various of its APIs wrap internal state and protocols of systemd
313 (e.g. logind and udev databases), which are not considered
314 stable. Hence, using static libraries is not recommended since it
315 generally means that version of the static libsystemd linked into
316 applications and the host systemd are not in sync, and will thus create
317 compatibility problems.
319 In addition, it is possible to disable the use of
320 libsystemd-shared-<suffix>.so for various components (via the
321 configuration options '-Dlink-*-shared'). In this mode, the libsystemd
322 and libsystemd-shared code is linked statically into selected
323 binaries. This option is intended for systems where some of the
324 components are intended to be delivered independently of the main
325 systemd package. Finally, some binaries can be compiled in a second
326 version (via the configuration option '-Dstandalone-binaries'). The
327 version suffixed with ".standalone" has the libsystemd and
328 libsystemd-shared code linked statically. Those binaries are intended
329 as replacements to be used in limited installations where the full
330 systemd suite is not installed. Yet another option is to rebuild
331 systemd with a different '-Dshared-lib-tag' setting, allowing different
332 systemd binaries to be linked to instances of the private shared
333 library that can be installed in parallel.
335 Again: Using the default shared linking is recommended, building static
336 or "standalone" versions is not. Mixing versions of systemd components
337 that would normally be built and used together (in particular various
338 daemons and the manager) is not recommended: we do not test such
339 combinations upstream and cannot provide support. Distributors making
340 use of those options are responsible if things do not work as expected.
343 Default udev rules use the following standard system group names, which
344 need to be resolvable by getgrnam() at any time, even in the very early
345 boot stages, where no other databases and network are available:
347 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
349 During runtime, the journal daemon requires the "systemd-journal" system
350 group to exist. New journal files will be readable by this group (but
351 not writable), which may be used to grant specific users read access. In
352 addition, system groups "wheel" and "adm" will be given read-only access
353 to journal files using systemd-tmpfiles-setup.service.
355 The journal remote daemon requires the "systemd-journal-remote" system
356 user and group to exist. During execution this network facing service
357 will drop privileges and assume this uid/gid for security reasons.
359 Similarly, the network management daemon requires the "systemd-network"
360 system user and group to exist.
362 Similarly, the name resolution daemon requires the "systemd-resolve"
363 system user and group to exist.
365 Similarly, the coredump support requires the "systemd-coredump" system
366 user and group to exist.
369 systemd ships with four glibc NSS modules:
371 nss-myhostname resolves the local hostname to locally configured IP
372 addresses, as well as "localhost" to 127.0.0.1/::1.
374 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
375 caching stub resolver "systemd-resolved".
377 nss-mymachines enables resolution of all local containers registered
378 with machined to their respective IP addresses.
380 nss-systemd enables resolution of users/group registered via the
381 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
382 including all dynamically allocated service users. (See the
383 DynamicUser= setting in unit files.)
385 To make use of these NSS modules, please add them to the "hosts:",
386 "passwd:", "group:", "shadow:" and "gshadow:" lines in
389 The four modules should be used in the following order:
391 passwd: files systemd
392 group: files [SUCCESS=merge] systemd
393 shadow: files systemd
394 gshadow: files systemd
395 hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
398 When calling "systemctl enable/disable/is-enabled" on a unit which is a
399 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
400 this needs to translate the action into the distribution specific
401 mechanism such as chkconfig or update-rc.d. Packagers need to provide
402 this script if you need this functionality (you don't if you disabled
405 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
406 needs to look like, and provide an implementation at the marked places.
408 WARNINGS and TAINT FLAGS:
409 systemd requires that the /run mount point exists. systemd also
410 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
411 will be set when this condition is detected.
413 Systemd will also warn when the cgroup support is unavailable in the
414 kernel (taint flag 'cgroups-missing'), the system is using the old
415 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
416 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
417 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
418 and 'overflowgid-not-65534'), the UID or GID range assigned to the
419 running systemd instance covers less than 0…65534 (taint flags
420 'short-uid-range' and 'short-gid-range').
422 Taint conditions are logged during boot, but may also be checked at any
425 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
427 See org.freedesktop.systemd1(5) for more information.
430 To run systemd under valgrind, compile systemd with the valgrind
431 development headers available (i.e. valgrind-devel or equivalent).
432 Otherwise, false positives will be triggered by code which violates
433 some rules but is actually safe. Note that valgrind generates nice
434 output only on exit(), hence on shutdown we don't execve()
437 STABLE BRANCHES AND BACKPORTS:
438 Stable branches with backported patches are available in the
439 systemd-stable repo at https://github.com/systemd/systemd-stable.
441 Stable branches are started for certain releases of systemd and named
442 after them, e.g. v238-stable. Stable branches are managed by
443 distribution maintainers on an as needed basis. See
444 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
445 more information and examples.