README

   1 systemd System and Service Manager
   2
   3 DETAILS:
   4         http://0pointer.de/blog/projects/systemd.html
   5
   6 WEB SITE:
   7         https://www.freedesktop.org/wiki/Software/systemd
   8
   9 GIT:
  10         git@github.com:systemd/systemd.git
  11         https://github.com/systemd/systemd
  12
  13 MAILING LIST:
  14         https://lists.freedesktop.org/mailman/listinfo/systemd-devel
  15
  16 IRC:
  17         #systemd on irc.libera.chat
  18
  19 BUG REPORTS:
  20         https://github.com/systemd/systemd/issues
  21
  22 AUTHOR:
  23         Lennart Poettering
  24         Kay Sievers
  25         ...and many others
  26
  27 LICENSE:
  28         LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
  29
  30 REQUIREMENTS:
  31         Linux kernel >= 3.13
  32         Linux kernel >= 4.2 for unified cgroup hierarchy support
  33         Linux kernel >= 4.10 for cgroup-bpf egress and ingress hooks
  34         Linux kernel >= 4.15 for cgroup-bpf device hook
  35         Linux kernel >= 4.17 for cgroup-bpf socket address hooks
  36         Linux kernel >= 5.3 for bounded-loops in BPF program
  37         Linux kernel >= 5.4 for signed Verity images support
  38         Linux kernel >= 5.7 for BPF links and the BPF LSM hook
  39
  40         Kernel Config Options:
  41           CONFIG_DEVTMPFS
  42           CONFIG_CGROUPS (it is OK to disable all controllers)
  43           CONFIG_INOTIFY_USER
  44           CONFIG_SIGNALFD
  45           CONFIG_TIMERFD
  46           CONFIG_EPOLL
  47           CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
  48           CONFIG_SYSFS
  49           CONFIG_PROC_FS
  50           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  51
  52         Kernel crypto/hash API
  53           CONFIG_CRYPTO_USER_API_HASH
  54           CONFIG_CRYPTO_HMAC
  55           CONFIG_CRYPTO_SHA256
  56
  57         udev will fail to work with the legacy sysfs layout:
  58           CONFIG_SYSFS_DEPRECATED=n
  59
  60         Legacy hotplug slows down the system and confuses udev:
  61           CONFIG_UEVENT_HELPER_PATH=""
  62
  63         Userspace firmware loading is not supported and should
  64         be disabled in the kernel:
  65           CONFIG_FW_LOADER_USER_HELPER=n
  66
  67         Some udev rules and virtualization detection relies on it:
  68           CONFIG_DMIID
  69
  70         Support for some SCSI devices serial number retrieval, to
  71         create additional symlinks in /dev/disk/ and /dev/tape:
  72           CONFIG_BLK_DEV_BSG
  73
  74         Required for PrivateNetwork= in service units:
  75           CONFIG_NET_NS
  76         Note that systemd-localed.service and other systemd units use
  77         PrivateNetwork so this is effectively required.
  78
  79         Required for PrivateUsers= in service units:
  80           CONFIG_USER_NS
  81
  82         Optional but strongly recommended:
  83           CONFIG_IPV6
  84           CONFIG_AUTOFS_FS
  85           CONFIG_TMPFS_XATTR
  86           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  87           CONFIG_SECCOMP
  88           CONFIG_SECCOMP_FILTER (required for seccomp support)
  89           CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
  90
  91         Required for CPUShares= in resource control unit settings
  92           CONFIG_CGROUP_SCHED
  93           CONFIG_FAIR_GROUP_SCHED
  94
  95         Required for CPUQuota= in resource control unit settings
  96           CONFIG_CFS_BANDWIDTH
  97
  98         Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
  99         IPEgressFilterPath= in resource control unit settings
 100         unit settings
 101           CONFIG_BPF
 102           CONFIG_BPF_SYSCALL
 103           CONFIG_BPF_JIT
 104           CONFIG_HAVE_EBPF_JIT
 105           CONFIG_CGROUP_BPF
 106
 107         Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
 108         resource control unit settings
 109           CONFIG_BPF
 110           CONFIG_BPF_SYSCALL
 111           CONFIG_BPF_JIT
 112           CONFIG_HAVE_EBPF_JIT
 113           CONFIG_CGROUP_BPF
 114
 115         For UEFI systems:
 116           CONFIG_EFIVAR_FS
 117           CONFIG_EFI_PARTITION
 118
 119         Required for signed Verity images support:
 120           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 121
 122         Required for RestrictFileSystems= in service units:
 123           CONFIG_BPF
 124           CONFIG_BPF_SYSCALL
 125           CONFIG_BPF_LSM
 126           CONFIG_DEBUG_INFO_BTF
 127           CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
 128
 129         We recommend to turn off Real-Time group scheduling in the
 130         kernel when using systemd. RT group scheduling effectively
 131         makes RT scheduling unavailable for most userspace, since it
 132         requires explicit assignment of RT budgets to each unit whose
 133         processes making use of RT. As there's no sensible way to
 134         assign these budgets automatically this cannot really be
 135         fixed, and it's best to disable group scheduling hence.
 136            CONFIG_RT_GROUP_SCHED=n
 137
 138         It's a good idea to disable the implicit creation of networking bonding
 139         devices by the kernel networking bonding module, so that the
 140         automatically created "bond0" interface doesn't conflict with any such
 141         device created by systemd-networkd (or other tools). Ideally there
 142         would be a kernel compile-time option for this, but there currently
 143         isn't. The next best thing is to make this change through a modprobe.d
 144         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 145
 146         Required for systemd-nspawn:
 147           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 148
 149         Required for systemd-oomd:
 150           CONFIG_PSI
 151
 152         Note that kernel auditing is broken when used with systemd's
 153         container code. When using systemd in conjunction with
 154         containers, please make sure to either turn off auditing at
 155         runtime using the kernel command line option "audit=0", or
 156         turn it off at kernel compile time using:
 157           CONFIG_AUDIT=n
 158         If systemd is compiled with libseccomp support on
 159         architectures which do not use socketcall() and where seccomp
 160         is supported (this effectively means x86-64 and ARM, but
 161         excludes 32-bit x86!), then nspawn will now install a
 162         work-around seccomp filter that makes containers boot even
 163         with audit being enabled. This works correctly only on kernels
 164         3.14 and newer though. TL;DR: turn audit off, still.
 165
 166         glibc >= 2.16
 167         libcap
 168         libmount >= 2.30 (from util-linux)
 169                 (util-linux *must* be built without --enable-libmount-support-mtab)
 170         libseccomp >= 2.3.1 (optional)
 171         libblkid >= 2.24 (from util-linux) (optional)
 172         libkmod >= 15 (optional)
 173         PAM >= 1.1.2 (optional)
 174         libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
 175         libaudit (optional)
 176         libacl (optional)
 177         libbpf >= 0.2.0 (optional)
 178         libfdisk >= 2.33 (from util-linux) (optional)
 179         libselinux (optional)
 180         liblzma (optional)
 181         liblz4 >= 1.3.0 / 130 (optional)
 182         libzstd >= 1.4.0 (optional)
 183         libgcrypt (optional)
 184         libqrencode (optional)
 185         libmicrohttpd (optional)
 186         libpython (optional)
 187         libidn2 or libidn (optional)
 188         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 189         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 190         elfutils >= 158 (optional)
 191         polkit (optional)
 192         tzdata >= 2014f (optional)
 193         pkg-config
 194         gperf
 195         docbook-xsl (optional, required for documentation)
 196         xsltproc    (optional, required for documentation)
 197         python-jinja2
 198         python-lxml (optional, required to build the indices)
 199         python >= 3.5
 200         meson >= 0.53.2 (>= 0.54.0 is required to build with 'meson compile')
 201         ninja
 202         gcc, awk, sed, grep, and similar tools
 203         clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
 204                 from source code in C)
 205         gnu-efi >= 3.0.5 (optional, required for systemd-boot)
 206
 207         During runtime, you need the following additional
 208         dependencies:
 209
 210         util-linux >= v2.27.1 required
 211         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 212                 NOTE: If using dbus < 1.9.18, you should override the default
 213                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 214         dracut (optional)
 215         polkit (optional)
 216
 217         To build in directory build/:
 218           meson setup build/ && meson compile -C build/
 219
 220         Any configuration options can be specified as -Darg=value... arguments
 221         to meson. After the build directory is initially configured, meson will
 222         refuse to run again, and options must be changed with:
 223           meson configure -Darg=value build/
 224         meson configure without any arguments will print out available options and
 225         their current values.
 226
 227         Useful commands:
 228           meson compile -v -C build/ some/target
 229           meson test -C build/
 230           sudo meson install -C build/
 231           DESTDIR=... meson install -C build/
 232
 233         A tarball can be created with:
 234           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 235
 236         When systemd-hostnamed is used, it is strongly recommended to
 237         install nss-myhostname to ensure that, in a world of
 238         dynamically changing hostnames, the hostname stays resolvable
 239         under all circumstances. In fact, systemd-hostnamed will warn
 240         if nss-myhostname is not installed.
 241
 242         nss-systemd must be enabled on systemd systems, as that's required for
 243         DynamicUser= to work. Note that we ship services out-of-the-box that
 244         make use of DynamicUser= now, hence enabling nss-systemd is not
 245         optional.
 246
 247         Note that the build prefix for systemd must be /usr. (Moreover,
 248         packages systemd relies on — such as D-Bus — really should use the same
 249         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 250         default and does not need to be specified) is the recommended setting.
 251         -Dsplit-usr=true can be used to give a semblance of support for systems
 252         with programs installed split between / and /usr. Moving everything
 253         under /usr is strongly encouraged.
 254
 255         Additional packages are necessary to run some tests:
 256         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 257         - nc                 (used by test/TEST-12-ISSUE-3171)
 258         - python3-pyparsing
 259         - python3-evdev      (used by hwdb parsing tests)
 260         - strace             (used by test/test-functions)
 261         - capsh              (optional, used by test-execute)
 262
 263 USERS AND GROUPS:
 264         Default udev rules use the following standard system group
 265         names, which need to be resolvable by getgrnam() at any time,
 266         even in the very early boot stages, where no other databases
 267         and network are available:
 268
 269         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 270
 271         During runtime, the journal daemon requires the
 272         "systemd-journal" system group to exist. New journal files will
 273         be readable by this group (but not writable), which may be used
 274         to grant specific users read access. In addition, system
 275         groups "wheel" and "adm" will be given read-only access to
 276         journal files using systemd-tmpfiles.service.
 277
 278         The journal remote daemon requires the
 279         "systemd-journal-remote" system user and group to
 280         exist. During execution this network facing service will drop
 281         privileges and assume this uid/gid for security reasons.
 282
 283         Similarly, the network management daemon requires the
 284         "systemd-network" system user and group to exist.
 285
 286         Similarly, the name resolution daemon requires the
 287         "systemd-resolve" system user and group to exist.
 288
 289         Similarly, the coredump support requires the
 290         "systemd-coredump" system user and group to exist.
 291
 292 NSS:
 293         systemd ships with four glibc NSS modules:
 294
 295         nss-myhostname resolves the local hostname to locally configured IP
 296         addresses, as well as "localhost" to 127.0.0.1/::1.
 297
 298         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 299         caching stub resolver "systemd-resolved".
 300
 301         nss-mymachines enables resolution of all local containers registered
 302         with machined to their respective IP addresses.
 303
 304         nss-systemd enables resolution of users/group registered via the
 305         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 306         including all dynamically allocated service users. (See the
 307         DynamicUser= setting in unit files.)
 308
 309         To make use of these NSS modules, please add them to the "hosts:",
 310         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 311         module should replace the glibc "dns" module in this file (and don't
 312         worry, it chain-loads the "dns" module if it can't talk to resolved).
 313
 314         The four modules should be used in the following order:
 315
 316                 passwd: compat systemd
 317                 group: compat systemd
 318                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 319
 320 SYSV INIT.D SCRIPTS:
 321         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 322         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 323         this needs to translate the action into the distribution specific
 324         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 325         this script if you need this functionality (you don't if you disabled
 326         SysV init support).
 327
 328         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 329         needs to look like, and provide an implementation at the marked places.
 330
 331 WARNINGS:
 332         systemd will warn during early boot if /usr is not already mounted at
 333         this point (that means: either located on the same file system as / or
 334         already mounted in the initrd). While in systemd itself very little
 335         will break if /usr is on a separate, late-mounted partition, many of
 336         its dependencies very likely will break sooner or later in one form or
 337         another. For example, udev rules tend to refer to binaries in /usr,
 338         binaries that link to libraries in /usr or binaries that refer to data
 339         files in /usr. Since these breakages are not always directly visible,
 340         systemd will warn about this, since this kind of file system setup is
 341         not really supported anymore by the basic set of Linux OS components.
 342
 343         systemd requires that the /run mount point exists. systemd also
 344         requires that /var/run is a symlink to /run.
 345
 346         For more information on this issue consult
 347         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 348
 349         To run systemd under valgrind, compile with meson option
 350         -Dvalgrind=true and have valgrind development headers installed
 351         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 352         triggered by code which violates some rules but is actually safe. Note
 353         that valgrind generates nice output only on exit(), hence on shutdown
 354         we don't execve() systemd-shutdown.
 355
 356 STABLE BRANCHES AND BACKPORTS:
 357         Stable branches with backported patches are available in the
 358         systemd-stable repo at https://github.com/systemd/systemd-stable.
 359
 360         Stable branches are started for certain releases of systemd and named
 361         after them, e.g. v238-stable. Stable branches are managed by
 362         distribution maintainers on an as needed basis. See
 363         https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 364         more information and examples.