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 reading credentials from SMBIOS:
141 Required for RestrictFileSystems= in service units:
145 CONFIG_DEBUG_INFO_BTF
146 CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
148 We recommend to turn off Real-Time group scheduling in the kernel when
149 using systemd. RT group scheduling effectively makes RT scheduling
150 unavailable for most userspace, since it requires explicit assignment of
151 RT budgets to each unit whose processes making use of RT. As there's no
152 sensible way to assign these budgets automatically this cannot really be
153 fixed, and it's best to disable group scheduling hence:
154 CONFIG_RT_GROUP_SCHED=n
156 It's a good idea to disable the implicit creation of networking bonding
157 devices by the kernel networking bonding module, so that the
158 automatically created "bond0" interface doesn't conflict with any such
159 device created by systemd-networkd (or other tools). Ideally there would
160 be a kernel compile-time option for this, but there currently isn't. The
161 next best thing is to make this change through a modprobe.d drop-in.
162 This is shipped by default, see modprobe.d/systemd.conf.
164 Required for systemd-nspawn:
165 CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
167 Required for systemd-oomd:
170 Note that kernel auditing is broken when used with systemd's container
171 code. When using systemd in conjunction with containers, please make
172 sure to either turn off auditing at runtime using the kernel command
173 line option "audit=0", or turn it off at kernel compile time using:
176 If systemd is compiled with libseccomp support on architectures which do
177 not use socketcall() and where seccomp is supported (this effectively
178 means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now
179 install a work-around seccomp filter that makes containers boot even
180 with audit being enabled. This works correctly only on kernels 3.14 and
181 newer though. TL;DR: turn audit off, still.
185 libmount >= 2.30 (from util-linux)
186 (util-linux *must* be built without --enable-libmount-support-mtab)
187 libseccomp >= 2.3.1 (optional)
188 libblkid >= 2.24 (from util-linux) (optional)
189 libkmod >= 15 (optional)
190 PAM >= 1.1.2 (optional)
191 libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
194 libbpf >= 0.1.0 (optional)
195 libfdisk >= 2.32 (from util-linux) (optional)
196 libselinux (optional)
198 liblz4 >= 1.3.0 / 130 (optional)
199 libzstd >= 1.4.0 (optional)
201 libqrencode (optional)
202 libmicrohttpd (optional)
203 libidn2 or libidn (optional)
204 gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
205 openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
206 elfutils >= 158 (optional)
208 tzdata >= 2014f (optional)
211 docbook-xsl (optional, required for documentation)
212 xsltproc (optional, required for documentation)
213 python >= 3.7 (required by meson too, >= 3.9 is required for ukify)
215 python-pefile (optional, required for ukify)
216 python-lxml (optional, required to build the indices)
217 pyelftools (optional, required for systemd-boot)
221 awk, sed, grep, and similar tools
222 clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
223 from source code in C)
225 During runtime, you need the following additional
228 util-linux >= v2.27.1 required (including but not limited to: mount,
229 umount, swapon, swapoff, sulogin,
231 dbus >= 1.4.0 (strictly speaking optional, but recommended)
232 NOTE: If using dbus < 1.9.18, you should override the default
233 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
237 To build in directory build/:
238 meson setup build/ && ninja -C build/
240 Any configuration options can be specified as -Darg=value... arguments
241 to meson. After the build directory is initially configured, meson will
242 refuse to run again, and options must be changed with:
243 meson configure -Darg=value build/
244 meson configure without any arguments will print out available options and
245 their current values.
248 ninja -C build -v some/target
250 sudo meson install -C build/ --no-rebuild
251 DESTDIR=... meson install -C build/
253 A tarball can be created with:
254 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
256 When systemd-hostnamed is used, it is strongly recommended to install
257 nss-myhostname to ensure that, in a world of dynamically changing
258 hostnames, the hostname stays resolvable under all circumstances. In
259 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
261 nss-systemd must be enabled on systemd systems, as that's required for
262 DynamicUser= to work. Note that we ship services out-of-the-box that
263 make use of DynamicUser= now, hence enabling nss-systemd is not
266 Note that the build prefix for systemd must be /usr/. (Moreover, packages
267 systemd relies on — such as D-Bus — really should use the same prefix,
268 otherwise you are on your own.) Split-usr and unmerged-usr systems are no
269 longer supported, and moving everything under /usr/ is required. Systems
270 with a separate /usr/ partition must mount it before transitioning into it
271 (i.e.: from the initrd). For more information see:
272 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
273 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
275 Additional packages are necessary to run some tests:
276 - nc (used by test/TEST-12-ISSUE-3171)
277 - python (test-udev which is installed is in python)
279 - python-evdev (used by hwdb parsing tests)
280 - strace (used by test/test-functions)
281 - capsh (optional, used by test-execute)
283 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
284 systemd main branch and latest major or stable releases are generally
285 expected to compile on current versions of popular distributions (at
286 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
287 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
288 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
289 attempt to support also other non-EOL versions of various distros.
290 Features which would break compilation on slightly older distributions
291 will only be introduced if there are significant reasons for this
292 (i.e. supporting them interferes with development or requires too many
293 resources to support). In some cases backports of specific libraries or
294 tools might be required.
296 The policy is similar for architecture support. systemd is regularly
297 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
298 and s390x), but should compile and work also on other architectures, for
299 which support has been added. systemd will emit warnings when
300 architecture-specific constants are not defined.
302 STATIC COMPILATION AND "STANDALONE" BINARIES:
303 systemd provides a public shared libraries libsystemd.so and
304 libudev.so. The latter is deprecated, and the sd-device APIs in
305 libsystemd should be used instead for new code. In addition, systemd is
306 built with a private shared library, libsystemd-shared-<suffix>.so,
307 that also includes the libsystemd code, and by default most systemd
308 binaries are linked to it. Using shared libraries saves disk space and
309 memory at runtime, because only one copy of the code is needed.
311 It is possible to build static versions of systemd public shared
312 libraries (via the configuration options '-Dstatic-libsystemd' and
313 '-Dstatic-libudev'). This allows the libsystemd and libudev code to be
314 linked statically into programs. Note that mixing & matching different
315 versions of libsystemd and systemd is generally not recommended, since
316 various of its APIs wrap internal state and protocols of systemd
317 (e.g. logind and udev databases), which are not considered
318 stable. Hence, using static libraries is not recommended since it
319 generally means that version of the static libsystemd linked into
320 applications and the host systemd are not in sync, and will thus create
321 compatibility problems.
323 In addition, it is possible to disable the use of
324 libsystemd-shared-<suffix>.so for various components (via the
325 configuration options '-Dlink-*-shared'). In this mode, the libsystemd
326 and libsystemd-shared code is linked statically into selected
327 binaries. This option is intended for systems where some of the
328 components are intended to be delivered independently of the main
329 systemd package. Finally, some binaries can be compiled in a second
330 version (via the configuration option '-Dstandalone-binaries'). The
331 version suffixed with ".standalone" has the libsystemd and
332 libsystemd-shared code linked statically. Those binaries are intended
333 as replacements to be used in limited installations where the full
334 systemd suite is not installed. Yet another option is to rebuild
335 systemd with a different '-Dshared-lib-tag' setting, allowing different
336 systemd binaries to be linked to instances of the private shared
337 library that can be installed in parallel.
339 Again: Using the default shared linking is recommended, building static
340 or "standalone" versions is not. Mixing versions of systemd components
341 that would normally be built and used together (in particular various
342 daemons and the manager) is not recommended: we do not test such
343 combinations upstream and cannot provide support. Distributors making
344 use of those options are responsible if things do not work as expected.
347 Default udev rules use the following standard system group names, which
348 need to be resolvable by getgrnam() at any time, even in the very early
349 boot stages, where no other databases and network are available:
351 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
353 During runtime, the journal daemon requires the "systemd-journal" system
354 group to exist. New journal files will be readable by this group (but
355 not writable), which may be used to grant specific users read access. In
356 addition, system groups "wheel" and "adm" will be given read-only access
357 to journal files using systemd-tmpfiles-setup.service.
359 The journal remote daemon requires the "systemd-journal-remote" system
360 user and group to exist. During execution this network facing service
361 will drop privileges and assume this uid/gid for security reasons.
363 Similarly, the network management daemon requires the "systemd-network"
364 system user and group to exist.
366 Similarly, the name resolution daemon requires the "systemd-resolve"
367 system user and group to exist.
369 Similarly, the coredump support requires the "systemd-coredump" system
370 user and group to exist.
373 systemd ships with four glibc NSS modules:
375 nss-myhostname resolves the local hostname to locally configured IP
376 addresses, as well as "localhost" to 127.0.0.1/::1.
378 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
379 caching stub resolver "systemd-resolved".
381 nss-mymachines enables resolution of all local containers registered
382 with machined to their respective IP addresses.
384 nss-systemd enables resolution of users/group registered via the
385 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
386 including all dynamically allocated service users. (See the
387 DynamicUser= setting in unit files.)
389 To make use of these NSS modules, please add them to the "hosts:",
390 "passwd:", "group:", "shadow:" and "gshadow:" lines in
393 The four modules should be used in the following order:
395 passwd: files systemd
396 group: files [SUCCESS=merge] systemd
397 shadow: files systemd
398 gshadow: files systemd
399 hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
402 When calling "systemctl enable/disable/is-enabled" on a unit which is a
403 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
404 this needs to translate the action into the distribution specific
405 mechanism such as chkconfig or update-rc.d. Packagers need to provide
406 this script if you need this functionality (you don't if you disabled
409 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
410 needs to look like, and provide an implementation at the marked places.
412 WARNINGS and TAINT FLAGS:
413 systemd requires that the /run mount point exists. systemd also
414 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
415 will be set when this condition is detected.
417 Systemd will also warn when the cgroup support is unavailable in the
418 kernel (taint flag 'cgroups-missing'), the system is using the old
419 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
420 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
421 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
422 and 'overflowgid-not-65534'), the UID or GID range assigned to the
423 running systemd instance covers less than 0…65534 (taint flags
424 'short-uid-range' and 'short-gid-range').
426 Taint conditions are logged during boot, but may also be checked at any
429 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
431 See org.freedesktop.systemd1(5) for more information.
434 To run systemd under valgrind, compile systemd with the valgrind
435 development headers available (i.e. valgrind-devel or equivalent).
436 Otherwise, false positives will be triggered by code which violates
437 some rules but is actually safe. Note that valgrind generates nice
438 output only on exit(), hence on shutdown we don't execve()
441 STABLE BRANCHES AND BACKPORTS:
442 Stable branches with backported patches are available in the
443 systemd-stable repo at https://github.com/systemd/systemd-stable.
445 Stable branches are started for certain releases of systemd and named
446 after them, e.g. v238-stable. Stable branches are managed by
447 distribution maintainers on an as needed basis. See
448 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
449 more information and examples.