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
21 http://0pointer.de/blog/projects/systemd.html
22 https://www.freedesktop.org/wiki/Software/systemd
30 LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
34 ≥ 4.3 for ambient capabilities
35 ≥ 4.5 for pids controller in cgroup v2
36 ≥ 4.6 for cgroup namespaces
37 ≥ 4.9 for RENAME_NOREPLACE support in vfat
38 ≥ 4.10 for cgroup-bpf egress and ingress hooks
39 ≥ 4.15 for cgroup-bpf device hook and cpu controller in cgroup v2
40 ≥ 4.17 for cgroup-bpf socket address hooks
41 ≥ 4.20 for PSI (used by systemd-oomd)
42 ≥ 5.3 for bounded loops in BPF program
43 ≥ 5.4 for signed Verity images
44 ≥ 5.7 for BPF links and the BPF LSM hook
46 Kernel versions below 4.15 have significant gaps in functionality and
47 are not recommended for use with this version of systemd. Taint flag
48 'old-kernel' will be set. Systemd will most likely still function, but
49 upstream support and testing are limited.
51 Kernel Config Options:
53 CONFIG_CGROUPS (it is OK to disable all controllers)
58 CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
61 CONFIG_FHANDLE (libudev, mount and bind mount handling)
63 Kernel crypto/hash API:
64 CONFIG_CRYPTO_USER_API_HASH
68 udev will fail to work with the legacy sysfs layout:
69 CONFIG_SYSFS_DEPRECATED=n
71 Legacy hotplug slows down the system and confuses udev:
72 CONFIG_UEVENT_HELPER_PATH=""
74 Userspace firmware loading is not supported and should be disabled in
76 CONFIG_FW_LOADER_USER_HELPER=n
78 Some udev rules and virtualization detection relies on it:
81 Support for some SCSI devices serial number retrieval, to create
82 additional symlinks in /dev/disk/ and /dev/tape:
85 Required for PrivateNetwork= in service units:
87 Note that systemd-localed.service and other systemd units use
88 PrivateNetwork so this is effectively required.
90 Required for PrivateUsers= in service units:
93 Optional but strongly recommended:
97 CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
99 CONFIG_SECCOMP_FILTER (required for seccomp support)
100 CONFIG_KCMP (for the kcmp() syscall, used to be under
101 CONFIG_CHECKPOINT_RESTORE before ~5.12)
103 Required for CPUShares= in resource control unit settings:
105 CONFIG_FAIR_GROUP_SCHED
107 Required for CPUQuota= in resource control unit settings:
110 Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
111 IPEgressFilterPath= in resource control unit settings unit settings:
118 Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
119 resource control unit settings:
130 Required for signed Verity images support:
131 CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
133 Required for RestrictFileSystems= in service units:
137 CONFIG_DEBUG_INFO_BTF
138 CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
140 We recommend to turn off Real-Time group scheduling in the kernel when
141 using systemd. RT group scheduling effectively makes RT scheduling
142 unavailable for most userspace, since it requires explicit assignment of
143 RT budgets to each unit whose processes making use of RT. As there's no
144 sensible way to assign these budgets automatically this cannot really be
145 fixed, and it's best to disable group scheduling hence:
146 CONFIG_RT_GROUP_SCHED=n
148 It's a good idea to disable the implicit creation of networking bonding
149 devices by the kernel networking bonding module, so that the
150 automatically created "bond0" interface doesn't conflict with any such
151 device created by systemd-networkd (or other tools). Ideally there would
152 be a kernel compile-time option for this, but there currently isn't. The
153 next best thing is to make this change through a modprobe.d drop-in.
154 This is shipped by default, see modprobe.d/systemd.conf.
156 Required for systemd-nspawn:
157 CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
159 Required for systemd-oomd:
162 Note that kernel auditing is broken when used with systemd's container
163 code. When using systemd in conjunction with containers, please make
164 sure to either turn off auditing at runtime using the kernel command
165 line option "audit=0", or turn it off at kernel compile time using:
167 If systemd is compiled with libseccomp support on architectures which do
168 not use socketcall() and where seccomp is supported (this effectively
169 means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now
170 install a work-around seccomp filter that makes containers boot even
171 with audit being enabled. This works correctly only on kernels 3.14 and
172 newer though. TL;DR: turn audit off, still.
176 libmount >= 2.30 (from util-linux)
177 (util-linux *must* be built without --enable-libmount-support-mtab)
178 libseccomp >= 2.3.1 (optional)
179 libblkid >= 2.24 (from util-linux) (optional)
180 libkmod >= 15 (optional)
181 PAM >= 1.1.2 (optional)
182 libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
185 libbpf >= 0.2.0 (optional)
186 libfdisk >= 2.32 (from util-linux) (optional)
187 libselinux (optional)
189 liblz4 >= 1.3.0 / 130 (optional)
190 libzstd >= 1.4.0 (optional)
192 libqrencode (optional)
193 libmicrohttpd (optional)
195 libidn2 or libidn (optional)
196 gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
197 openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
198 elfutils >= 158 (optional)
200 tzdata >= 2014f (optional)
203 docbook-xsl (optional, required for documentation)
204 xsltproc (optional, required for documentation)
206 python-lxml (optional, required to build the indices)
211 awk, sed, grep, and similar tools
212 clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
213 from source code in C)
214 gnu-efi >= 3.0.5 (optional, required for systemd-boot)
216 During runtime, you need the following additional
219 util-linux >= v2.27.1 required
220 dbus >= 1.4.0 (strictly speaking optional, but recommended)
221 NOTE: If using dbus < 1.9.18, you should override the default
222 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
226 To build in directory build/:
227 meson setup build/ && ninja -C build/
229 Any configuration options can be specified as -Darg=value... arguments
230 to meson. After the build directory is initially configured, meson will
231 refuse to run again, and options must be changed with:
232 meson configure -Darg=value build/
233 meson configure without any arguments will print out available options and
234 their current values.
237 ninja -C build -v some/target
239 sudo meson install -C build/ --no-rebuild
240 DESTDIR=... meson install -C build/
242 A tarball can be created with:
243 v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
245 When systemd-hostnamed is used, it is strongly recommended to install
246 nss-myhostname to ensure that, in a world of dynamically changing
247 hostnames, the hostname stays resolvable under all circumstances. In
248 fact, systemd-hostnamed will warn if nss-myhostname is not installed.
250 nss-systemd must be enabled on systemd systems, as that's required for
251 DynamicUser= to work. Note that we ship services out-of-the-box that
252 make use of DynamicUser= now, hence enabling nss-systemd is not
255 Note that the build prefix for systemd must be /usr. (Moreover, packages
256 systemd relies on — such as D-Bus — really should use the same prefix,
257 otherwise you are on your own.) -Dsplit-usr=false (which is the default
258 and does not need to be specified) is the recommended setting.
259 -Dsplit-usr=true can be used to give a semblance of support for systems
260 with programs installed split between / and /usr. Moving everything
261 under /usr is strongly encouraged.
263 Additional packages are necessary to run some tests:
264 - busybox (used by test/TEST-13-NSPAWN-SMOKE)
265 - nc (used by test/TEST-12-ISSUE-3171)
267 - python3-evdev (used by hwdb parsing tests)
268 - strace (used by test/test-functions)
269 - capsh (optional, used by test-execute)
271 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
273 systemd main branch and latest major or stable releases are generally
274 expected to compile on current versions of popular distributions (at
275 least all non-EOL versions of Fedora, Debian unstable/testing/stable,
276 latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
277 CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
278 attempt to support also other non-EOL versions of various distros.
279 Features which would break compilation on slightly-older distributions
280 will only be introduced if there are significant reasons for this
281 (i.e. supporting them interferes with development or requires too many
282 resources to support). In some cases backports of specific libraries or
283 tools might be required.
285 The policy is similar wrt. architecture support. systemd is regularly
286 tested on popular architectures (currently amd64, i386, arm64, ppc64el,
287 and s390x), but should compile and work also on other architectures, for
288 which support has been added. systemd will emit warnings when
289 architecture-specific constants are not defined.
292 Default udev rules use the following standard system group names, which
293 need to be resolvable by getgrnam() at any time, even in the very early
294 boot stages, where no other databases and network are available:
296 audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
298 During runtime, the journal daemon requires the "systemd-journal" system
299 group to exist. New journal files will be readable by this group (but
300 not writable), which may be used to grant specific users read access. In
301 addition, system groups "wheel" and "adm" will be given read-only access
302 to journal files using systemd-tmpfiles.service.
304 The journal remote daemon requires the "systemd-journal-remote" system
305 user and group to exist. During execution this network facing service
306 will drop privileges and assume this uid/gid for security reasons.
308 Similarly, the network management daemon requires the "systemd-network"
309 system user and group to exist.
311 Similarly, the name resolution daemon requires the "systemd-resolve"
312 system user and group to exist.
314 Similarly, the coredump support requires the "systemd-coredump" system
315 user and group to exist.
318 systemd ships with four glibc NSS modules:
320 nss-myhostname resolves the local hostname to locally configured IP
321 addresses, as well as "localhost" to 127.0.0.1/::1.
323 nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
324 caching stub resolver "systemd-resolved".
326 nss-mymachines enables resolution of all local containers registered
327 with machined to their respective IP addresses.
329 nss-systemd enables resolution of users/group registered via the
330 User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
331 including all dynamically allocated service users. (See the
332 DynamicUser= setting in unit files.)
334 To make use of these NSS modules, please add them to the "hosts:",
335 "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module
336 should replace the glibc "dns" module in this file (and don't worry, it
337 chain-loads the "dns" module if it can't talk to resolved).
339 The four modules should be used in the following order:
341 passwd: compat systemd
342 group: compat systemd
343 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
346 When calling "systemctl enable/disable/is-enabled" on a unit which is a
347 SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
348 this needs to translate the action into the distribution specific
349 mechanism such as chkconfig or update-rc.d. Packagers need to provide
350 this script if you need this functionality (you don't if you disabled
353 Please see src/systemctl/systemd-sysv-install.SKELETON for how this
354 needs to look like, and provide an implementation at the marked places.
356 WARNINGS and TAINT FLAGS:
357 systemd will warn during early boot if /usr is not already mounted at
358 this point (that means: either located on the same file system as / or
359 already mounted in the initrd). While in systemd itself very little
360 will break if /usr is on a separate late-mounted partition, many of its
361 dependencies very likely will break sooner or later in one form or
362 another. For example, udev rules tend to refer to binaries in /usr,
363 binaries that link to libraries in /usr, or binaries that refer to data
364 files in /usr. Since these breakages are not always directly visible,
365 systemd will warn about this. Such setups are not really supported by
366 the basic set of Linux OS components. Taint flag 'split-usr' will be
367 set when this condition is detected.
369 For more information on this issue consult
370 https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
372 systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin
373 and /lib* are not symlinks to their counterparts under /usr). Taint flag
374 'unmerged-usr' will be set when this condition is detected.
376 For more information on this issue consult
377 https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
379 systemd requires that the /run mount point exists. systemd also
380 requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
381 will be set when this condition is detected.
383 Systemd will also warn when the cgroup support is unavailable in the
384 kernel (taint flag 'cgroups-missing'), the system is using the old
385 cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
386 running in non-UTC mode (taint flag 'local-hwclock'), the kernel
387 overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
388 and 'overflowgid-not-65534'), the UID or GID range assigned to the
389 running systemd instance covers less than 0…65534 (taint flags
390 'short-uid-range' and 'short-gid-range').
392 Taint conditions are logged during boot, but may also be checked at any
395 busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
397 See org.freedesktop.systemd1(5) for more information.
400 To run systemd under valgrind, compile with meson option
401 -Dvalgrind=true and have valgrind development headers installed
402 (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
403 triggered by code which violates some rules but is actually safe. Note
404 that valgrind generates nice output only on exit(), hence on shutdown
405 we don't execve() systemd-shutdown.
407 STABLE BRANCHES AND BACKPORTS:
408 Stable branches with backported patches are available in the
409 systemd-stable repo at https://github.com/systemd/systemd-stable.
411 Stable branches are started for certain releases of systemd and named
412 after them, e.g. v238-stable. Stable branches are managed by
413 distribution maintainers on an as needed basis. See
414 https://www.freedesktop.org/wiki/Software/systemd/Backports for some
415 more information and examples.