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)
210 python-lxml (optional, required to build the indices)
215 awk, sed, grep, and similar tools
216 clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
217 from source code in C)
218 gnu-efi >= 3.0.5 (optional, required for systemd-boot)
220 During runtime, you need the following additional
223 util-linux >= v2.27.1 required
224 dbus >= 1.4.0 (strictly speaking optional, but recommended)
225 NOTE: If using dbus < 1.9.18, you should override the default
226 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
230 To build in directory build/:
231 meson setup build/ && ninja -C build/
233 Any configuration options can be specified as -Darg=value... arguments
234 to meson. After the build directory is initially configured, meson will
235 refuse to run again, and options must be changed with:
236 meson configure -Darg=value build/
237 meson configure without any arguments will print out available options and
238 their current values.
241 ninja -C build -v some/target
243 sudo meson install -C build/ --no-rebuild
244 DESTDIR=... meson install -C build/
246 A tarball can be created with:
247 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
249 When systemd-hostnamed is used, it is strongly recommended to install
250 nss-myhostname to ensure that, in a world of dynamically changing
251 hostnames, the hostname stays resolvable under all circumstances. In
252 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
254 nss-systemd must be enabled on systemd systems, as that's required for
255 DynamicUser= to work. Note that we ship services out-of-the-box that
256 make use of DynamicUser= now, hence enabling nss-systemd is not
259 Note that the build prefix for systemd must be /usr. (Moreover, packages
260 systemd relies on — such as D-Bus — really should use the same prefix,
261 otherwise you are on your own.) -Dsplit-usr=false (which is the default
262 and does not need to be specified) is the recommended setting.
263 -Dsplit-usr=true can be used to give a semblance of support for systems
264 with programs installed split between / and /usr. Moving everything
265 under /usr is strongly encouraged.
267 Additional packages are necessary to run some tests:
268 - busybox (used by test/TEST-13-NSPAWN-SMOKE)
269 - nc (used by test/TEST-12-ISSUE-3171)
271 - python3-evdev (used by hwdb parsing tests)
272 - strace (used by test/test-functions)
273 - capsh (optional, used by test-execute)
275 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
276 systemd main branch and latest major or stable releases are generally
277 expected to compile on current versions of popular distributions (at
278 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
279 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
280 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
281 attempt to support also other non-EOL versions of various distros.
282 Features which would break compilation on slightly-older distributions
283 will only be introduced if there are significant reasons for this
284 (i.e. supporting them interferes with development or requires too many
285 resources to support). In some cases backports of specific libraries or
286 tools might be required.
288 The policy is similar wrt. architecture support. systemd is regularly
289 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
290 and s390x), but should compile and work also on other architectures, for
291 which support has been added. systemd will emit warnings when
292 architecture-specific constants are not defined.
295 Default udev rules use the following standard system group names, which
296 need to be resolvable by getgrnam() at any time, even in the very early
297 boot stages, where no other databases and network are available:
299 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
301 During runtime, the journal daemon requires the "systemd-journal" system
302 group to exist. New journal files will be readable by this group (but
303 not writable), which may be used to grant specific users read access. In
304 addition, system groups "wheel" and "adm" will be given read-only access
305 to journal files using systemd-tmpfiles.service.
307 The journal remote daemon requires the "systemd-journal-remote" system
308 user and group to exist. During execution this network facing service
309 will drop privileges and assume this uid/gid for security reasons.
311 Similarly, the network management daemon requires the "systemd-network"
312 system user and group to exist.
314 Similarly, the name resolution daemon requires the "systemd-resolve"
315 system user and group to exist.
317 Similarly, the coredump support requires the "systemd-coredump" system
318 user and group to exist.
321 systemd ships with four glibc NSS modules:
323 nss-myhostname resolves the local hostname to locally configured IP
324 addresses, as well as "localhost" to 127.0.0.1/::1.
326 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
327 caching stub resolver "systemd-resolved".
329 nss-mymachines enables resolution of all local containers registered
330 with machined to their respective IP addresses.
332 nss-systemd enables resolution of users/group registered via the
333 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
334 including all dynamically allocated service users. (See the
335 DynamicUser= setting in unit files.)
337 To make use of these NSS modules, please add them to the "hosts:",
338 "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module
339 should replace the glibc "dns" module in this file (and don't worry, it
340 chain-loads the "dns" module if it can't talk to resolved).
342 The four modules should be used in the following order:
344 passwd: compat systemd
345 group: compat systemd
346 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
349 When calling "systemctl enable/disable/is-enabled" on a unit which is a
350 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
351 this needs to translate the action into the distribution specific
352 mechanism such as chkconfig or update-rc.d. Packagers need to provide
353 this script if you need this functionality (you don't if you disabled
356 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
357 needs to look like, and provide an implementation at the marked places.
359 WARNINGS and TAINT FLAGS:
360 systemd will warn during early boot if /usr is not already mounted at
361 this point (that means: either located on the same file system as / or
362 already mounted in the initrd). While in systemd itself very little
363 will break if /usr is on a separate late-mounted partition, many of its
364 dependencies very likely will break sooner or later in one form or
365 another. For example, udev rules tend to refer to binaries in /usr,
366 binaries that link to libraries in /usr, or binaries that refer to data
367 files in /usr. Since these breakages are not always directly visible,
368 systemd will warn about this. Such setups are not really supported by
369 the basic set of Linux OS components. Taint flag 'split-usr' will be
370 set when this condition is detected.
372 For more information on this issue consult
373 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
375 systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin
376 and /lib* are not symlinks to their counterparts under /usr). Taint flag
377 'unmerged-usr' will be set when this condition is detected.
379 For more information on this issue consult
380 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
382 systemd requires that the /run mount point exists. systemd also
383 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
384 will be set when this condition is detected.
386 Systemd will also warn when the cgroup support is unavailable in the
387 kernel (taint flag 'cgroups-missing'), the system is using the old
388 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
389 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
390 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
391 and 'overflowgid-not-65534'), the UID or GID range assigned to the
392 running systemd instance covers less than 0…65534 (taint flags
393 'short-uid-range' and 'short-gid-range').
395 Taint conditions are logged during boot, but may also be checked at any
398 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
400 See org.freedesktop.systemd1(5) for more information.
403 To run systemd under valgrind, compile with meson option
404 -Dvalgrind=true and have valgrind development headers installed
405 (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
406 triggered by code which violates some rules but is actually safe. Note
407 that valgrind generates nice output only on exit(), hence on shutdown
408 we don't execve() systemd-shutdown.
410 STABLE BRANCHES AND BACKPORTS:
411 Stable branches with backported patches are available in the
412 systemd-stable repo at https://github.com/systemd/systemd-stable.
414 Stable branches are started for certain releases of systemd and named
415 after them, e.g. v238-stable. Stable branches are managed by
416 distribution maintainers on an as needed basis. See
417 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
418 more information and examples.