README

   1 systemd System and Service Manager
   2
   3 WEB SITE:
   4         https://systemd.io
   5
   6 GIT:
   7         git@github.com:systemd/systemd.git
   8         https://github.com/systemd/systemd
   9
  10 MAILING LIST:
  11         https://lists.freedesktop.org/mailman/listinfo/systemd-devel
  12
  13 IRC:
  14         #systemd on irc.libera.chat
  15
  16 BUG REPORTS:
  17         https://github.com/systemd/systemd/issues
  18
  19 OLDER DOCUMENTATION:
  20
  21         http://0pointer.de/blog/projects/systemd.html
  22         https://www.freedesktop.org/wiki/Software/systemd
  23
  24 AUTHOR:
  25         Lennart Poettering
  26         Kay Sievers
  27         ...and many others
  28
  29 LICENSE:
  30         LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
  31
  32 REQUIREMENTS:
  33         Linux kernel ≥ 3.15
  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
  45
  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.
  50
  51         Kernel Config Options:
  52           CONFIG_DEVTMPFS
  53           CONFIG_CGROUPS (it is OK to disable all controllers)
  54           CONFIG_INOTIFY_USER
  55           CONFIG_SIGNALFD
  56           CONFIG_TIMERFD
  57           CONFIG_EPOLL
  58           CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
  59           CONFIG_SYSFS
  60           CONFIG_PROC_FS
  61           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  62
  63         Kernel crypto/hash API:
  64           CONFIG_CRYPTO_USER_API_HASH
  65           CONFIG_CRYPTO_HMAC
  66           CONFIG_CRYPTO_SHA256
  67
  68         udev will fail to work with the legacy sysfs layout:
  69           CONFIG_SYSFS_DEPRECATED=n
  70
  71         Legacy hotplug slows down the system and confuses udev:
  72           CONFIG_UEVENT_HELPER_PATH=""
  73
  74         Userspace firmware loading is not supported and should be disabled in
  75         the kernel:
  76           CONFIG_FW_LOADER_USER_HELPER=n
  77
  78         Some udev rules and virtualization detection relies on it:
  79           CONFIG_DMIID
  80
  81         Support for some SCSI devices serial number retrieval, to create
  82         additional symlinks in /dev/disk/ and /dev/tape:
  83           CONFIG_BLK_DEV_BSG
  84
  85         Required for PrivateNetwork= in service units:
  86           CONFIG_NET_NS
  87         Note that systemd-localed.service and other systemd units use
  88         PrivateNetwork so this is effectively required.
  89
  90         Required for PrivateUsers= in service units:
  91           CONFIG_USER_NS
  92
  93         Optional but strongly recommended:
  94           CONFIG_IPV6
  95           CONFIG_AUTOFS_FS
  96           CONFIG_TMPFS_XATTR
  97           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  98           CONFIG_SECCOMP
  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)
 102
 103         Required for CPUShares= in resource control unit settings:
 104           CONFIG_CGROUP_SCHED
 105           CONFIG_FAIR_GROUP_SCHED
 106
 107         Required for CPUQuota= in resource control unit settings:
 108           CONFIG_CFS_BANDWIDTH
 109
 110         Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
 111         IPEgressFilterPath= in resource control unit settings unit settings:
 112           CONFIG_BPF
 113           CONFIG_BPF_SYSCALL
 114           CONFIG_BPF_JIT
 115           CONFIG_HAVE_EBPF_JIT
 116           CONFIG_CGROUP_BPF
 117
 118         Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
 119         resource control unit settings:
 120           CONFIG_BPF
 121           CONFIG_BPF_SYSCALL
 122           CONFIG_BPF_JIT
 123           CONFIG_HAVE_EBPF_JIT
 124           CONFIG_CGROUP_BPF
 125
 126         For UEFI systems:
 127           CONFIG_EFIVAR_FS
 128           CONFIG_EFI_PARTITION
 129
 130         Required for signed Verity images support:
 131           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 132
 133         Required for RestrictFileSystems= in service units:
 134           CONFIG_BPF
 135           CONFIG_BPF_SYSCALL
 136           CONFIG_BPF_LSM
 137           CONFIG_DEBUG_INFO_BTF
 138           CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
 139
 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
 147
 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.
 155
 156         Required for systemd-nspawn:
 157           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 158
 159         Required for systemd-oomd:
 160           CONFIG_PSI
 161
 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:
 166           CONFIG_AUDIT=n
 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.
 173
 174         glibc >= 2.16
 175         libcap
 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
 183         libaudit (optional)
 184         libacl (optional)
 185         libbpf >= 0.2.0 (optional)
 186         libfdisk >= 2.32 (from util-linux) (optional)
 187         libselinux (optional)
 188         liblzma (optional)
 189         liblz4 >= 1.3.0 / 130 (optional)
 190         libzstd >= 1.4.0 (optional)
 191         libgcrypt (optional)
 192         libqrencode (optional)
 193         libmicrohttpd (optional)
 194         libpython (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)
 199         polkit (optional)
 200         tzdata >= 2014f (optional)
 201         pkg-config
 202         gperf
 203         docbook-xsl (optional, required for documentation)
 204         xsltproc    (optional, required for documentation)
 205         python-jinja2
 206         python-lxml (optional, required to build the indices)
 207         python >= 3.5
 208         meson >= 0.53.2
 209         ninja
 210         gcc >= 4.7
 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)
 215
 216         During runtime, you need the following additional
 217         dependencies:
 218
 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).
 223         dracut (optional)
 224         polkit (optional)
 225
 226         To build in directory build/:
 227           meson setup build/ && ninja -C build/
 228
 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.
 235
 236         Useful commands:
 237           ninja -C build -v some/target
 238           meson test -C build/
 239           sudo meson install -C build/ --no-rebuild
 240           DESTDIR=... meson install -C build/
 241
 242         A tarball can be created with:
 243           v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
 244
 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.
 249
 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
 253         optional.
 254
 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.
 262
 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)
 266         - python3-pyparsing
 267         - python3-evdev      (used by hwdb parsing tests)
 268         - strace             (used by test/test-functions)
 269         - capsh              (optional, used by test-execute)
 270
 271 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
 272
 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.
 284
 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.
 290
 291 USERS AND GROUPS:
 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:
 295
 296         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 297
 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.
 303
 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.
 307
 308         Similarly, the network management daemon requires the "systemd-network"
 309         system user and group to exist.
 310
 311         Similarly, the name resolution daemon requires the "systemd-resolve"
 312         system user and group to exist.
 313
 314         Similarly, the coredump support requires the "systemd-coredump" system
 315         user and group to exist.
 316
 317 NSS:
 318         systemd ships with four glibc NSS modules:
 319
 320         nss-myhostname resolves the local hostname to locally configured IP
 321         addresses, as well as "localhost" to 127.0.0.1/::1.
 322
 323         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 324         caching stub resolver "systemd-resolved".
 325
 326         nss-mymachines enables resolution of all local containers registered
 327         with machined to their respective IP addresses.
 328
 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.)
 333
 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).
 338
 339         The four modules should be used in the following order:
 340
 341                 passwd: compat systemd
 342                 group: compat systemd
 343                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 344
 345 SYSV INIT.D SCRIPTS:
 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
 351         SysV init support).
 352
 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.
 355
 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.
 368
 369         For more information on this issue consult
 370         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 371
 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.
 375
 376         For more information on this issue consult
 377         https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
 378
 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.
 382
 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').
 391
 392         Taint conditions are logged during boot, but may also be checked at any
 393         time with:
 394
 395           busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
 396
 397         See org.freedesktop.systemd1(5) for more information.
 398
 399 VALGRIND:
 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.
 406
 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.
 410
 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.