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, awk, sed, grep, and similar tools
 211         clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
 212                 from source code in C)
 213         gnu-efi >= 3.0.5 (optional, required for systemd-boot)
 214
 215         During runtime, you need the following additional
 216         dependencies:
 217
 218         util-linux >= v2.27.1 required
 219         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 220                 NOTE: If using dbus < 1.9.18, you should override the default
 221                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 222         dracut (optional)
 223         polkit (optional)
 224
 225         To build in directory build/:
 226           meson setup build/ && ninja -C build/
 227
 228         Any configuration options can be specified as -Darg=value... arguments
 229         to meson. After the build directory is initially configured, meson will
 230         refuse to run again, and options must be changed with:
 231           meson configure -Darg=value build/
 232         meson configure without any arguments will print out available options and
 233         their current values.
 234
 235         Useful commands:
 236           ninja -C build -v some/target
 237           meson test -C build/
 238           sudo meson install -C build/ --no-rebuild
 239           DESTDIR=... meson install -C build/
 240
 241         A tarball can be created with:
 242           v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
 243
 244         When systemd-hostnamed is used, it is strongly recommended to install
 245         nss-myhostname to ensure that, in a world of dynamically changing
 246         hostnames, the hostname stays resolvable under all circumstances. In
 247         fact, systemd-hostnamed will warn if nss-myhostname is not installed.
 248
 249         nss-systemd must be enabled on systemd systems, as that's required for
 250         DynamicUser= to work. Note that we ship services out-of-the-box that
 251         make use of DynamicUser= now, hence enabling nss-systemd is not
 252         optional.
 253
 254         Note that the build prefix for systemd must be /usr. (Moreover, packages
 255         systemd relies on — such as D-Bus — really should use the same prefix,
 256         otherwise you are on your own.) -Dsplit-usr=false (which is the default
 257         and does not need to be specified) is the recommended setting.
 258         -Dsplit-usr=true can be used to give a semblance of support for systems
 259         with programs installed split between / and /usr. Moving everything
 260         under /usr is strongly encouraged.
 261
 262         Additional packages are necessary to run some tests:
 263         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 264         - nc                 (used by test/TEST-12-ISSUE-3171)
 265         - python3-pyparsing
 266         - python3-evdev      (used by hwdb parsing tests)
 267         - strace             (used by test/test-functions)
 268         - capsh              (optional, used by test-execute)
 269
 270 POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
 271
 272         systemd main branch and latest major or stable releases are generally
 273         expected to compile on current versions of popular distributions (at
 274         least all non-EOL versions of Fedora, Debian unstable/testing/stable,
 275         latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
 276         CentOS Stream 8 and 9, up-to-date Arch, etc.)  We will generally
 277         attempt to support also other non-EOL versions of various distros.
 278         Features which would break compilation on slightly-older distributions
 279         will only be introduced if there are significant reasons for this
 280         (i.e. supporting them interferes with development or requires too many
 281         resources to support). In some cases backports of specific libraries or
 282         tools might be required.
 283
 284         The policy is similar wrt. architecture support. systemd is regularly
 285         tested on popular architectures (currently amd64, i386, arm64, ppc64el,
 286         and s390x), but should compile and work also on other architectures, for
 287         which support has been added. systemd will emit warnings when
 288         architecture-specific constants are not defined.
 289
 290 USERS AND GROUPS:
 291         Default udev rules use the following standard system group names, which
 292         need to be resolvable by getgrnam() at any time, even in the very early
 293         boot stages, where no other databases and network are available:
 294
 295         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 296
 297         During runtime, the journal daemon requires the "systemd-journal" system
 298         group to exist. New journal files will be readable by this group (but
 299         not writable), which may be used to grant specific users read access. In
 300         addition, system groups "wheel" and "adm" will be given read-only access
 301         to journal files using systemd-tmpfiles.service.
 302
 303         The journal remote daemon requires the "systemd-journal-remote" system
 304         user and group to exist. During execution this network facing service
 305         will drop privileges and assume this uid/gid for security reasons.
 306
 307         Similarly, the network management daemon requires the "systemd-network"
 308         system user and group to exist.
 309
 310         Similarly, the name resolution daemon requires the "systemd-resolve"
 311         system user and group to exist.
 312
 313         Similarly, the coredump support requires the "systemd-coredump" system
 314         user and group to exist.
 315
 316 NSS:
 317         systemd ships with four glibc NSS modules:
 318
 319         nss-myhostname resolves the local hostname to locally configured IP
 320         addresses, as well as "localhost" to 127.0.0.1/::1.
 321
 322         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 323         caching stub resolver "systemd-resolved".
 324
 325         nss-mymachines enables resolution of all local containers registered
 326         with machined to their respective IP addresses.
 327
 328         nss-systemd enables resolution of users/group registered via the
 329         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 330         including all dynamically allocated service users. (See the
 331         DynamicUser= setting in unit files.)
 332
 333         To make use of these NSS modules, please add them to the "hosts:",
 334         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module
 335         should replace the glibc "dns" module in this file (and don't worry, it
 336         chain-loads the "dns" module if it can't talk to resolved).
 337
 338         The four modules should be used in the following order:
 339
 340                 passwd: compat systemd
 341                 group: compat systemd
 342                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 343
 344 SYSV INIT.D SCRIPTS:
 345         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 346         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 347         this needs to translate the action into the distribution specific
 348         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 349         this script if you need this functionality (you don't if you disabled
 350         SysV init support).
 351
 352         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 353         needs to look like, and provide an implementation at the marked places.
 354
 355 WARNINGS and TAINT FLAGS:
 356         systemd will warn during early boot if /usr is not already mounted at
 357         this point (that means: either located on the same file system as / or
 358         already mounted in the initrd). While in systemd itself very little
 359         will break if /usr is on a separate late-mounted partition, many of its
 360         dependencies very likely will break sooner or later in one form or
 361         another. For example, udev rules tend to refer to binaries in /usr,
 362         binaries that link to libraries in /usr or binaries that refer to data
 363         files in /usr. Since these breakages are not always directly visible,
 364         systemd will warn about this. Such setups are not really supported by
 365         the basic set of Linux OS components. Taint flag 'split-usr' will be
 366         set when this condition is detected.
 367
 368         For more information on this issue consult
 369         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 370
 371         systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin
 372         and /lib* are not symlinks to their counterparts under /usr). Taint flag
 373         'unmerged-usr' will be set when this condition is detected.
 374
 375         For more information on this issue consult
 376         https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge
 377
 378         systemd requires that the /run mount point exists. systemd also
 379         requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
 380         will be set when this condition is detected.
 381
 382         Systemd will also warn when the cgroup support is unavailable in the
 383         kernel (taint flag 'cgroups-missing'), the system is using the old
 384         cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
 385         running in non-UTC mode (taint flag 'local-hwclock'), the kernel
 386         overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
 387         and 'overflowgid-not-65534'), the UID or GID range assigned to the
 388         running systemd instance covers less than 0…65534 (taint flags
 389         'short-uid-range' and 'short-gid-range').
 390
 391         Taint conditions are logged during boot, but may also be checked at any
 392         time with:
 393
 394           busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
 395
 396 VALGRIND:
 397         To run systemd under valgrind, compile with meson option
 398         -Dvalgrind=true and have valgrind development headers installed
 399         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 400         triggered by code which violates some rules but is actually safe. Note
 401         that valgrind generates nice output only on exit(), hence on shutdown
 402         we don't execve() systemd-shutdown.
 403
 404 STABLE BRANCHES AND BACKPORTS:
 405         Stable branches with backported patches are available in the
 406         systemd-stable repo at https://github.com/systemd/systemd-stable.
 407
 408         Stable branches are started for certain releases of systemd and named
 409         after them, e.g. v238-stable. Stable branches are managed by
 410         distribution maintainers on an as needed basis. See
 411         https://www.freedesktop.org/wiki/Software/systemd/Backports for some
 412         more information and examples.