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)
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)
211 python-lxml (optional, required to build the indices)
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)
219 gnu-efi >= 3.0.5 (optional, required for systemd-boot)
221 During runtime, you need the following additional
224 util-linux >= v2.27.1 required
225 dbus >= 1.4.0 (strictly speaking optional, but recommended)
226 NOTE: If using dbus < 1.9.18, you should override the default
227 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
231 To build in directory build/:
232 meson setup build/ && ninja -C build/
234 Any configuration options can be specified as -Darg=value... arguments
235 to meson. After the build directory is initially configured, meson will
236 refuse to run again, and options must be changed with:
237 meson configure -Darg=value build/
238 meson configure without any arguments will print out available options and
239 their current values.
242 ninja -C build -v some/target
244 sudo meson install -C build/ --no-rebuild
245 DESTDIR=... meson install -C build/
247 A tarball can be created with:
248 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
250 When systemd-hostnamed is used, it is strongly recommended to install
251 nss-myhostname to ensure that, in a world of dynamically changing
252 hostnames, the hostname stays resolvable under all circumstances. In
253 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
255 nss-systemd must be enabled on systemd systems, as that's required for
256 DynamicUser= to work. Note that we ship services out-of-the-box that
257 make use of DynamicUser= now, hence enabling nss-systemd is not
260 Note that the build prefix for systemd must be /usr. (Moreover, packages
261 systemd relies on — such as D-Bus — really should use the same prefix,
262 otherwise you are on your own.) -Dsplit-usr=false (which is the default
263 and does not need to be specified) is the recommended setting.
264 -Dsplit-usr=true can be used to give a semblance of support for systems
265 with programs installed split between / and /usr. Moving everything
266 under /usr is strongly encouraged.
268 Additional packages are necessary to run some tests:
269 - busybox (used by test/TEST-13-NSPAWN-SMOKE)
270 - nc (used by test/TEST-12-ISSUE-3171)
272 - python3-evdev (used by hwdb parsing tests)
273 - strace (used by test/test-functions)
274 - capsh (optional, used by test-execute)
276 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
277 systemd main branch and latest major or stable releases are generally
278 expected to compile on current versions of popular distributions (at
279 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
280 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
281 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
282 attempt to support also other non-EOL versions of various distros.
283 Features which would break compilation on slightly-older distributions
284 will only be introduced if there are significant reasons for this
285 (i.e. supporting them interferes with development or requires too many
286 resources to support). In some cases backports of specific libraries or
287 tools might be required.
289 The policy is similar wrt. architecture support. systemd is regularly
290 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
291 and s390x), but should compile and work also on other architectures, for
292 which support has been added. systemd will emit warnings when
293 architecture-specific constants are not defined.
296 Default udev rules use the following standard system group names, which
297 need to be resolvable by getgrnam() at any time, even in the very early
298 boot stages, where no other databases and network are available:
300 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
302 During runtime, the journal daemon requires the "systemd-journal" system
303 group to exist. New journal files will be readable by this group (but
304 not writable), which may be used to grant specific users read access. In
305 addition, system groups "wheel" and "adm" will be given read-only access
306 to journal files using systemd-tmpfiles.service.
308 The journal remote daemon requires the "systemd-journal-remote" system
309 user and group to exist. During execution this network facing service
310 will drop privileges and assume this uid/gid for security reasons.
312 Similarly, the network management daemon requires the "systemd-network"
313 system user and group to exist.
315 Similarly, the name resolution daemon requires the "systemd-resolve"
316 system user and group to exist.
318 Similarly, the coredump support requires the "systemd-coredump" system
319 user and group to exist.
322 systemd ships with four glibc NSS modules:
324 nss-myhostname resolves the local hostname to locally configured IP
325 addresses, as well as "localhost" to 127.0.0.1/::1.
327 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
328 caching stub resolver "systemd-resolved".
330 nss-mymachines enables resolution of all local containers registered
331 with machined to their respective IP addresses.
333 nss-systemd enables resolution of users/group registered via the
334 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
335 including all dynamically allocated service users. (See the
336 DynamicUser= setting in unit files.)
338 To make use of these NSS modules, please add them to the "hosts:",
339 "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module
340 should replace the glibc "dns" module in this file (and don't worry, it
341 chain-loads the "dns" module if it can't talk to resolved).
343 The four modules should be used in the following order:
345 passwd: compat systemd
346 group: compat systemd
347 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
350 When calling "systemctl enable/disable/is-enabled" on a unit which is a
351 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
352 this needs to translate the action into the distribution specific
353 mechanism such as chkconfig or update-rc.d. Packagers need to provide
354 this script if you need this functionality (you don't if you disabled
357 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
358 needs to look like, and provide an implementation at the marked places.
360 WARNINGS and TAINT FLAGS:
361 systemd will warn during early boot if /usr is not already mounted at
362 this point (that means: either located on the same file system as / or
363 already mounted in the initrd). While in systemd itself very little
364 will break if /usr is on a separate late-mounted partition, many of its
365 dependencies very likely will break sooner or later in one form or
366 another. For example, udev rules tend to refer to binaries in /usr,
367 binaries that link to libraries in /usr, or binaries that refer to data
368 files in /usr. Since these breakages are not always directly visible,
369 systemd will warn about this. Such setups are not really supported by
370 the basic set of Linux OS components. Taint flag 'split-usr' will be
371 set when this condition is detected.
373 For more information on this issue consult
374 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
376 systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin
377 and /lib* are not symlinks to their counterparts under /usr). Taint flag
378 'unmerged-usr' will be set when this condition is detected.
380 For more information on this issue consult
381 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
383 systemd requires that the /run mount point exists. systemd also
384 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
385 will be set when this condition is detected.
387 Systemd will also warn when the cgroup support is unavailable in the
388 kernel (taint flag 'cgroups-missing'), the system is using the old
389 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
390 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
391 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
392 and 'overflowgid-not-65534'), the UID or GID range assigned to the
393 running systemd instance covers less than 0…65534 (taint flags
394 'short-uid-range' and 'short-gid-range').
396 Taint conditions are logged during boot, but may also be checked at any
399 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
401 See org.freedesktop.systemd1(5) for more information.
404 To run systemd under valgrind, compile with meson option
405 -Dvalgrind=true and have valgrind development headers installed
406 (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
407 triggered by code which violates some rules but is actually safe. Note
408 that valgrind generates nice output only on exit(), hence on shutdown
409 we don't execve() systemd-shutdown.
411 STABLE BRANCHES AND BACKPORTS:
412 Stable branches with backported patches are available in the
413 systemd-stable repo at https://github.com/systemd/systemd-stable.
415 Stable branches are started for certain releases of systemd and named
416 after them, e.g. v238-stable. Stable branches are managed by
417 distribution maintainers on an as needed basis. See
418 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
419 more information and examples.