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                      ≥ 4.5 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                      ≥ 5.3 for bounded loops in BPF program
  41                      ≥ 5.4 for signed Verity images
  42                      ≥ 5.7 for BPF links and the BPF LSM hook
  43
  44         Kernel versions below 4.15 have significant gaps in functionality and
  45         are not recommended for use with this version of systemd. Taint flag
  46         'old-kernel' will be set. Systemd will most likely still function, but
  47         upstream support and testing are limited.
  48
  49         Kernel Config Options:
  50           CONFIG_DEVTMPFS
  51           CONFIG_CGROUPS (it is OK to disable all controllers)
  52           CONFIG_INOTIFY_USER
  53           CONFIG_SIGNALFD
  54           CONFIG_TIMERFD
  55           CONFIG_EPOLL
  56           CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
  57           CONFIG_SYSFS
  58           CONFIG_PROC_FS
  59           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  60
  61         Kernel crypto/hash API
  62           CONFIG_CRYPTO_USER_API_HASH
  63           CONFIG_CRYPTO_HMAC
  64           CONFIG_CRYPTO_SHA256
  65
  66         udev will fail to work with the legacy sysfs layout:
  67           CONFIG_SYSFS_DEPRECATED=n
  68
  69         Legacy hotplug slows down the system and confuses udev:
  70           CONFIG_UEVENT_HELPER_PATH=""
  71
  72         Userspace firmware loading is not supported and should
  73         be disabled in the kernel:
  74           CONFIG_FW_LOADER_USER_HELPER=n
  75
  76         Some udev rules and virtualization detection relies on it:
  77           CONFIG_DMIID
  78
  79         Support for some SCSI devices serial number retrieval, to
  80         create additional symlinks in /dev/disk/ and /dev/tape:
  81           CONFIG_BLK_DEV_BSG
  82
  83         Required for PrivateNetwork= in service units:
  84           CONFIG_NET_NS
  85         Note that systemd-localed.service and other systemd units use
  86         PrivateNetwork so this is effectively required.
  87
  88         Required for PrivateUsers= in service units:
  89           CONFIG_USER_NS
  90
  91         Optional but strongly recommended:
  92           CONFIG_IPV6
  93           CONFIG_AUTOFS_FS
  94           CONFIG_TMPFS_XATTR
  95           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  96           CONFIG_SECCOMP
  97           CONFIG_SECCOMP_FILTER (required for seccomp support)
  98           CONFIG_KCMP (for the kcmp() syscall, used to be under CONFIG_CHECKPOINT_RESTORE before ~5.12)
  99
 100         Required for CPUShares= in resource control unit settings
 101           CONFIG_CGROUP_SCHED
 102           CONFIG_FAIR_GROUP_SCHED
 103
 104         Required for CPUQuota= in resource control unit settings
 105           CONFIG_CFS_BANDWIDTH
 106
 107         Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
 108         IPEgressFilterPath= in resource control unit settings
 109         unit settings
 110           CONFIG_BPF
 111           CONFIG_BPF_SYSCALL
 112           CONFIG_BPF_JIT
 113           CONFIG_HAVE_EBPF_JIT
 114           CONFIG_CGROUP_BPF
 115
 116         Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
 117         resource control unit settings
 118           CONFIG_BPF
 119           CONFIG_BPF_SYSCALL
 120           CONFIG_BPF_JIT
 121           CONFIG_HAVE_EBPF_JIT
 122           CONFIG_CGROUP_BPF
 123
 124         For UEFI systems:
 125           CONFIG_EFIVAR_FS
 126           CONFIG_EFI_PARTITION
 127
 128         Required for signed Verity images support:
 129           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 130
 131         Required for RestrictFileSystems= in service units:
 132           CONFIG_BPF
 133           CONFIG_BPF_SYSCALL
 134           CONFIG_BPF_LSM
 135           CONFIG_DEBUG_INFO_BTF
 136           CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
 137
 138         We recommend to turn off Real-Time group scheduling in the
 139         kernel when using systemd. RT group scheduling effectively
 140         makes RT scheduling unavailable for most userspace, since it
 141         requires explicit assignment of RT budgets to each unit whose
 142         processes making use of RT. As there's no sensible way to
 143         assign these budgets automatically this cannot really be
 144         fixed, and it's best to disable group scheduling hence.
 145            CONFIG_RT_GROUP_SCHED=n
 146
 147         It's a good idea to disable the implicit creation of networking bonding
 148         devices by the kernel networking bonding module, so that the
 149         automatically created "bond0" interface doesn't conflict with any such
 150         device created by systemd-networkd (or other tools). Ideally there
 151         would be a kernel compile-time option for this, but there currently
 152         isn't. The next best thing is to make this change through a modprobe.d
 153         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 154
 155         Required for systemd-nspawn:
 156           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 157
 158         Required for systemd-oomd:
 159           CONFIG_PSI
 160
 161         Note that kernel auditing is broken when used with systemd's
 162         container code. When using systemd in conjunction with
 163         containers, please make sure to either turn off auditing at
 164         runtime using the kernel command line option "audit=0", or
 165         turn it off at kernel compile time using:
 166           CONFIG_AUDIT=n
 167         If systemd is compiled with libseccomp support on
 168         architectures which do not use socketcall() and where seccomp
 169         is supported (this effectively means x86-64 and ARM, but
 170         excludes 32-bit x86!), then nspawn will now install a
 171         work-around seccomp filter that makes containers boot even
 172         with audit being enabled. This works correctly only on kernels
 173         3.14 and newer though. TL;DR: turn audit off, still.
 174
 175         glibc >= 2.16
 176         libcap
 177         libmount >= 2.30 (from util-linux)
 178                 (util-linux *must* be built without --enable-libmount-support-mtab)
 179         libseccomp >= 2.3.1 (optional)
 180         libblkid >= 2.24 (from util-linux) (optional)
 181         libkmod >= 15 (optional)
 182         PAM >= 1.1.2 (optional)
 183         libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
 184         libaudit (optional)
 185         libacl (optional)
 186         libbpf >= 0.2.0 (optional)
 187         libfdisk >= 2.32 (from util-linux) (optional)
 188         libselinux (optional)
 189         liblzma (optional)
 190         liblz4 >= 1.3.0 / 130 (optional)
 191         libzstd >= 1.4.0 (optional)
 192         libgcrypt (optional)
 193         libqrencode (optional)
 194         libmicrohttpd (optional)
 195         libpython (optional)
 196         libidn2 or libidn (optional)
 197         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 198         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 199         elfutils >= 158 (optional)
 200         polkit (optional)
 201         tzdata >= 2014f (optional)
 202         pkg-config
 203         gperf
 204         docbook-xsl (optional, required for documentation)
 205         xsltproc    (optional, required for documentation)
 206         python-jinja2
 207         python-lxml (optional, required to build the indices)
 208         python >= 3.5
 209         meson >= 0.53.2 (>= 0.54.0 is required to build with 'meson compile')
 210         ninja
 211         gcc, 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/ && meson compile -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           meson compile -v -C build/ some/target
 238           meson test -C build/
 239           sudo meson install -C build/
 240           DESTDIR=... meson install -C build/
 241
 242         A tarball can be created with:
 243           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 244
 245         When systemd-hostnamed is used, it is strongly recommended to
 246         install nss-myhostname to ensure that, in a world of
 247         dynamically changing hostnames, the hostname stays resolvable
 248         under all circumstances. In fact, systemd-hostnamed will warn
 249         if nss-myhostname is not installed.
 250
 251         nss-systemd must be enabled on systemd systems, as that's required for
 252         DynamicUser= to work. Note that we ship services out-of-the-box that
 253         make use of DynamicUser= now, hence enabling nss-systemd is not
 254         optional.
 255
 256         Note that the build prefix for systemd must be /usr. (Moreover,
 257         packages systemd relies on — such as D-Bus — really should use the same
 258         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 259         default and does not need to be specified) is the recommended setting.
 260         -Dsplit-usr=true can be used to give a semblance of support for systems
 261         with programs installed split between / and /usr. Moving everything
 262         under /usr is strongly encouraged.
 263
 264         Additional packages are necessary to run some tests:
 265         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 266         - nc                 (used by test/TEST-12-ISSUE-3171)
 267         - python3-pyparsing
 268         - python3-evdev      (used by hwdb parsing tests)
 269         - strace             (used by test/test-functions)
 270         - capsh              (optional, used by test-execute)
 271
 272 USERS AND GROUPS:
 273         Default udev rules use the following standard system group
 274         names, which need to be resolvable by getgrnam() at any time,
 275         even in the very early boot stages, where no other databases
 276         and network are available:
 277
 278         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 279
 280         During runtime, the journal daemon requires the
 281         "systemd-journal" system group to exist. New journal files will
 282         be readable by this group (but not writable), which may be used
 283         to grant specific users read access. In addition, system
 284         groups "wheel" and "adm" will be given read-only access to
 285         journal files using systemd-tmpfiles.service.
 286
 287         The journal remote daemon requires the
 288         "systemd-journal-remote" system user and group to
 289         exist. During execution this network facing service will drop
 290         privileges and assume this uid/gid for security reasons.
 291
 292         Similarly, the network management daemon requires the
 293         "systemd-network" system user and group to exist.
 294
 295         Similarly, the name resolution daemon requires the
 296         "systemd-resolve" system user and group to exist.
 297
 298         Similarly, the coredump support requires the
 299         "systemd-coredump" system user and group to exist.
 300
 301 NSS:
 302         systemd ships with four glibc NSS modules:
 303
 304         nss-myhostname resolves the local hostname to locally configured IP
 305         addresses, as well as "localhost" to 127.0.0.1/::1.
 306
 307         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 308         caching stub resolver "systemd-resolved".
 309
 310         nss-mymachines enables resolution of all local containers registered
 311         with machined to their respective IP addresses.
 312
 313         nss-systemd enables resolution of users/group registered via the
 314         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 315         including all dynamically allocated service users. (See the
 316         DynamicUser= setting in unit files.)
 317
 318         To make use of these NSS modules, please add them to the "hosts:",
 319         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 320         module should replace the glibc "dns" module in this file (and don't
 321         worry, it chain-loads the "dns" module if it can't talk to resolved).
 322
 323         The four modules should be used in the following order:
 324
 325                 passwd: compat systemd
 326                 group: compat systemd
 327                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 328
 329 SYSV INIT.D SCRIPTS:
 330         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 331         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 332         this needs to translate the action into the distribution specific
 333         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 334         this script if you need this functionality (you don't if you disabled
 335         SysV init support).
 336
 337         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 338         needs to look like, and provide an implementation at the marked places.
 339
 340 WARNINGS and TAINT FLAGS:
 341         systemd will warn during early boot if /usr is not already mounted at
 342         this point (that means: either located on the same file system as / or
 343         already mounted in the initrd). While in systemd itself very little
 344         will break if /usr is on a separate late-mounted partition, many of its
 345         dependencies very likely will break sooner or later in one form or
 346         another. For example, udev rules tend to refer to binaries in /usr,
 347         binaries that link to libraries in /usr or binaries that refer to data
 348         files in /usr. Since these breakages are not always directly visible,
 349         systemd will warn about this. Such setups are not really supported by
 350         the basic set of Linux OS components. Taint flag 'split-usr' will be
 351         set when this condition is detected.
 352
 353         For more information on this issue consult
 354         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 355
 356         systemd requires that the /run mount point exists. systemd also
 357         requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
 358         will be set when this condition is detected.
 359
 360         Systemd will also warn when the cgroup support is unavailable in the
 361         kernel (taint flag 'cgroups-missing'), the system is using the old
 362         cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
 363         running in non-UTC mode (taint flag 'local-hwclock'), the kernel
 364         overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
 365         and 'overflowgid-not-65534'), the UID or GID range assigned to the
 366         running systemd instance covers less than 0…65534 (taint flags
 367         'short-uid-range' and 'short-gid-range').
 368
 369         Taint conditions are logged during boot, but may also be checked at any
 370         time with:
 371
 372           busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
 373
 374 VALGRIND:
 375         To run systemd under valgrind, compile with meson option
 376         -Dvalgrind=true and have valgrind development headers installed
 377         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 378         triggered by code which violates some rules but is actually safe. Note
 379         that valgrind generates nice output only on exit(), hence on shutdown
 380         we don't execve() systemd-shutdown.
 381
 382 STABLE BRANCHES AND BACKPORTS:
 383         Stable branches with backported patches are available in the
 384         systemd-stable repo at https://github.com/systemd/systemd-stable.
 385
 386         Stable branches are started for certain releases of systemd and named
 387         after them, e.g. v238-stable. Stable branches are managed by
 388         distribution maintainers on an as needed basis. See
 389         https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 390         more information and examples.