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:
171 If systemd is compiled with libseccomp support on architectures which do
172 not use socketcall() and where seccomp is supported (this effectively
173 means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now
174 install a work-around seccomp filter that makes containers boot even
175 with audit being enabled. This works correctly only on kernels 3.14 and
176 newer though. TL;DR: turn audit off, still.
180 libmount >= 2.30 (from util-linux)
181 (util-linux *must* be built without --enable-libmount-support-mtab)
182 libseccomp >= 2.3.1 (optional)
183 libblkid >= 2.24 (from util-linux) (optional)
184 libkmod >= 15 (optional)
185 PAM >= 1.1.2 (optional)
186 libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
189 libbpf >= 0.1.0 (optional)
190 libfdisk >= 2.32 (from util-linux) (optional)
191 libselinux (optional)
193 liblz4 >= 1.3.0 / 130 (optional)
194 libzstd >= 1.4.0 (optional)
196 libqrencode (optional)
197 libmicrohttpd (optional)
198 libidn2 or libidn (optional)
199 gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
200 openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
201 elfutils >= 158 (optional)
203 tzdata >= 2014f (optional)
206 docbook-xsl (optional, required for documentation)
207 xsltproc (optional, required for documentation)
208 python >= 3.7 (required by meson too, >= 3.9 is required for ukify)
210 python-pefile (optional, required for ukify)
211 python-lxml (optional, required to build the indices)
212 pyelftools (optional, required for systemd-boot)
216 awk, sed, grep, and similar tools
217 clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
218 from source code in C)
220 During runtime, you need the following additional
223 util-linux >= v2.27.1 required (including but not limited to: mount,
224 umount, swapon, swapoff, sulogin,
226 dbus >= 1.4.0 (strictly speaking optional, but recommended)
227 NOTE: If using dbus < 1.9.18, you should override the default
228 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
232 To build in directory build/:
233 meson setup build/ && ninja -C build/
235 Any configuration options can be specified as -Darg=value... arguments
236 to meson. After the build directory is initially configured, meson will
237 refuse to run again, and options must be changed with:
238 meson configure -Darg=value build/
239 meson configure without any arguments will print out available options and
240 their current values.
243 ninja -C build -v some/target
245 sudo meson install -C build/ --no-rebuild
246 DESTDIR=... meson install -C build/
248 A tarball can be created with:
249 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
251 When systemd-hostnamed is used, it is strongly recommended to install
252 nss-myhostname to ensure that, in a world of dynamically changing
253 hostnames, the hostname stays resolvable under all circumstances. In
254 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
256 nss-systemd must be enabled on systemd systems, as that's required for
257 DynamicUser= to work. Note that we ship services out-of-the-box that
258 make use of DynamicUser= now, hence enabling nss-systemd is not
261 Note that the build prefix for systemd must be /usr. (Moreover, packages
262 systemd relies on — such as D-Bus — really should use the same prefix,
263 otherwise you are on your own.) -Dsplit-usr=false (which is the default
264 and does not need to be specified) is the recommended setting.
265 -Dsplit-usr=true can be used to give a semblance of support for systems
266 with programs installed split between / and /usr. Moving everything
267 under /usr is strongly encouraged.
269 Additional packages are necessary to run some tests:
270 - nc (used by test/TEST-12-ISSUE-3171)
271 - python (test-udev which is installed is in python)
273 - python-evdev (used by hwdb parsing tests)
274 - strace (used by test/test-functions)
275 - capsh (optional, used by test-execute)
277 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
278 systemd main branch and latest major or stable releases are generally
279 expected to compile on current versions of popular distributions (at
280 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
281 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
282 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
283 attempt to support also other non-EOL versions of various distros.
284 Features which would break compilation on slightly older distributions
285 will only be introduced if there are significant reasons for this
286 (i.e. supporting them interferes with development or requires too many
287 resources to support). In some cases backports of specific libraries or
288 tools might be required.
290 The policy is similar for architecture support. systemd is regularly
291 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
292 and s390x), but should compile and work also on other architectures, for
293 which support has been added. systemd will emit warnings when
294 architecture-specific constants are not defined.
296 STATIC COMPILATION AND "STANDALONE" BINARIES:
298 systemd provides a public shared libraries libsystemd.so and
299 libudev.so. The latter is deprecated, and the sd-device APIs in
300 libsystemd should be used instead for new code. In addition, systemd is
301 built with a private shared library, libsystemd-shared-<suffix>.so,
302 that also includes the libsystemd code, and by default most systemd
303 binaries are linked to it. Using shared libraries saves disk space and
304 memory at runtime, because only one copy of the code is needed.
306 It is possible to build static versions of systemd public shared
307 libraries (via the configuration options '-Dstatic-libsystemd' and
308 '-Dstatic-libudev'). This allows the libsystemd and libudev code to be
309 linked statically into programs. In addition, it is possible to disable
310 the use of libsystemd-shared-<suffix>.so for various components (via
311 the configuration options '-Dlink-*-shared'). In this mode, the
312 libsystemd and libsystemd-shared code is linked statically into
313 selected binaries. This option is intended for systems where some of
314 the components are intended to be delivered independently of the main
315 systemd package. Finally, some binaries can be compiled in a second
316 version (via the configuration option '-Dstandalone-binaries'). The
317 version suffixed with ".standalone" has the libsystemd and
318 libsystemd-shared code linked statically. Those binaries are intended
319 as replacements to be used in limited installations where the full
320 systemd is not installed. Yet another option is to rebuild systemd with
321 a different '-Dshared-lib-tag' setting, allowing different systemd
322 binaries to be linked to instances of the private shared library that
323 can be installed in parallel.
325 Using the default shared linking is recommended. Mixing versions of
326 systemd components that would normally be built and used together (in
327 particular various daemons and the manager) is not recommended: we do
328 not test such combinations upstream and cannot provide support.
329 Distributors making use of those options are responsible if things do
330 not work as expected.
333 Default udev rules use the following standard system group names, which
334 need to be resolvable by getgrnam() at any time, even in the very early
335 boot stages, where no other databases and network are available:
337 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
339 During runtime, the journal daemon requires the "systemd-journal" system
340 group to exist. New journal files will be readable by this group (but
341 not writable), which may be used to grant specific users read access. In
342 addition, system groups "wheel" and "adm" will be given read-only access
343 to journal files using systemd-tmpfiles-setup.service.
345 The journal remote daemon requires the "systemd-journal-remote" system
346 user and group to exist. During execution this network facing service
347 will drop privileges and assume this uid/gid for security reasons.
349 Similarly, the network management daemon requires the "systemd-network"
350 system user and group to exist.
352 Similarly, the name resolution daemon requires the "systemd-resolve"
353 system user and group to exist.
355 Similarly, the coredump support requires the "systemd-coredump" system
356 user and group to exist.
359 systemd ships with four glibc NSS modules:
361 nss-myhostname resolves the local hostname to locally configured IP
362 addresses, as well as "localhost" to 127.0.0.1/::1.
364 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
365 caching stub resolver "systemd-resolved".
367 nss-mymachines enables resolution of all local containers registered
368 with machined to their respective IP addresses.
370 nss-systemd enables resolution of users/group registered via the
371 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
372 including all dynamically allocated service users. (See the
373 DynamicUser= setting in unit files.)
375 To make use of these NSS modules, please add them to the "hosts:",
376 "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module
377 should replace the glibc "dns" module in this file (and don't worry, it
378 chain-loads the "dns" module if it can't talk to resolved).
380 The four modules should be used in the following order:
382 passwd: compat systemd
383 group: compat systemd
384 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
387 When calling "systemctl enable/disable/is-enabled" on a unit which is a
388 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
389 this needs to translate the action into the distribution specific
390 mechanism such as chkconfig or update-rc.d. Packagers need to provide
391 this script if you need this functionality (you don't if you disabled
394 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
395 needs to look like, and provide an implementation at the marked places.
397 WARNINGS and TAINT FLAGS:
398 systemd will warn during early boot if /usr is not already mounted at
399 this point (that means: either located on the same file system as / or
400 already mounted in the initrd). While in systemd itself very little
401 will break if /usr is on a separate late-mounted partition, many of its
402 dependencies very likely will break sooner or later in one form or
403 another. For example, udev rules tend to refer to binaries in /usr,
404 binaries that link to libraries in /usr, or binaries that refer to data
405 files in /usr. Since these breakages are not always directly visible,
406 systemd will warn about this. Such setups are not really supported by
407 the basic set of Linux OS components. Taint flag 'split-usr' will be
408 set when this condition is detected.
410 For more information on this issue consult
411 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
413 systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin
414 and /lib* are not symlinks to their counterparts under /usr). Taint flag
415 'unmerged-usr' will be set when this condition is detected.
417 For more information on this issue consult
418 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
420 systemd requires that the /run mount point exists. systemd also
421 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
422 will be set when this condition is detected.
424 Systemd will also warn when the cgroup support is unavailable in the
425 kernel (taint flag 'cgroups-missing'), the system is using the old
426 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
427 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
428 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
429 and 'overflowgid-not-65534'), the UID or GID range assigned to the
430 running systemd instance covers less than 0…65534 (taint flags
431 'short-uid-range' and 'short-gid-range').
433 Taint conditions are logged during boot, but may also be checked at any
436 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
438 See org.freedesktop.systemd1(5) for more information.
441 To run systemd under valgrind, compile systemd with the valgrind
442 development headers available (i.e. valgrind-devel or equivalent).
443 Otherwise, false positives will be triggered by code which violates
444 some rules but is actually safe. Note that valgrind generates nice
445 output only on exit(), hence on shutdown we don't execve()
448 STABLE BRANCHES AND BACKPORTS:
449 Stable branches with backported patches are available in the
450 systemd-stable repo at https://github.com/systemd/systemd-stable.
452 Stable branches are started for certain releases of systemd and named
453 after them, e.g. v238-stable. Stable branches are managed by
454 distribution maintainers on an as needed basis. See
455 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
456 more information and examples.