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         LGPLv2.1+ for all code
  29         - except src/basic/MurmurHash2.c which is Public Domain
  30         - except src/basic/siphash24.c which is CC0 Public Domain
  31         - except src/journal/lookup3.c which is Public Domain
  32         - except src/udev/* which is (currently still) GPLv2, GPLv2+
  33         - except tools/chromiumos/* which is BSD-style
  34
  35 REQUIREMENTS:
  36         Linux kernel >= 3.13
  37         Linux kernel >= 4.2 for unified cgroup hierarchy support
  38         Linux kernel >= 4.10 for cgroup-bpf egress and ingress hooks
  39         Linux kernel >= 4.15 for cgroup-bpf device hook
  40         Linux kernel >= 4.17 for cgroup-bpf socket address hooks
  41         Linux kernel >= 5.3 for bounded-loops in BPF program
  42         Linux kernel >= 5.4 for signed Verity images support
  43         Linux kernel >= 5.7 for BPF links
  44
  45         Kernel Config Options:
  46           CONFIG_DEVTMPFS
  47           CONFIG_CGROUPS (it is OK to disable all controllers)
  48           CONFIG_INOTIFY_USER
  49           CONFIG_SIGNALFD
  50           CONFIG_TIMERFD
  51           CONFIG_EPOLL
  52           CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
  53           CONFIG_SYSFS
  54           CONFIG_PROC_FS
  55           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  56
  57         Kernel crypto/hash API
  58           CONFIG_CRYPTO_USER_API_HASH
  59           CONFIG_CRYPTO_HMAC
  60           CONFIG_CRYPTO_SHA256
  61
  62         udev will fail to work with the legacy sysfs layout:
  63           CONFIG_SYSFS_DEPRECATED=n
  64
  65         Legacy hotplug slows down the system and confuses udev:
  66           CONFIG_UEVENT_HELPER_PATH=""
  67
  68         Userspace firmware loading is not supported and should
  69         be disabled in the kernel:
  70           CONFIG_FW_LOADER_USER_HELPER=n
  71
  72         Some udev rules and virtualization detection relies on it:
  73           CONFIG_DMIID
  74
  75         Support for some SCSI devices serial number retrieval, to
  76         create additional symlinks in /dev/disk/ and /dev/tape:
  77           CONFIG_BLK_DEV_BSG
  78
  79         Required for PrivateNetwork= in service units:
  80           CONFIG_NET_NS
  81         Note that systemd-localed.service and other systemd units use
  82         PrivateNetwork so this is effectively required.
  83
  84         Required for PrivateUsers= in service units:
  85           CONFIG_USER_NS
  86
  87         Optional but strongly recommended:
  88           CONFIG_IPV6
  89           CONFIG_AUTOFS_FS
  90           CONFIG_TMPFS_XATTR
  91           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  92           CONFIG_SECCOMP
  93           CONFIG_SECCOMP_FILTER (required for seccomp support)
  94           CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
  95
  96         Required for CPUShares= in resource control unit settings
  97           CONFIG_CGROUP_SCHED
  98           CONFIG_FAIR_GROUP_SCHED
  99
 100         Required for CPUQuota= in resource control unit settings
 101           CONFIG_CFS_BANDWIDTH
 102
 103         Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
 104         IPEgressFilterPath= in resource control unit settings
 105         unit settings
 106           CONFIG_BPF
 107           CONFIG_BPF_SYSCALL
 108           CONFIG_BPF_JIT
 109           CONFIG_HAVE_EBPF_JIT
 110           CONFIG_CGROUP_BPF
 111
 112         Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
 113         resource control unit settings
 114           CONFIG_BPF
 115           CONFIG_BPF_SYSCALL
 116           CONFIG_BPF_JIT
 117           CONFIG_HAVE_EBPF_JIT
 118           CONFIG_CGROUP_BPF
 119
 120         For UEFI systems:
 121           CONFIG_EFIVAR_FS
 122           CONFIG_EFI_PARTITION
 123
 124         Required for signed Verity images support:
 125           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 126
 127         We recommend to turn off Real-Time group scheduling in the
 128         kernel when using systemd. RT group scheduling effectively
 129         makes RT scheduling unavailable for most userspace, since it
 130         requires explicit assignment of RT budgets to each unit whose
 131         processes making use of RT. As there's no sensible way to
 132         assign these budgets automatically this cannot really be
 133         fixed, and it's best to disable group scheduling hence.
 134            CONFIG_RT_GROUP_SCHED=n
 135
 136         It's a good idea to disable the implicit creation of networking bonding
 137         devices by the kernel networking bonding module, so that the
 138         automatically created "bond0" interface doesn't conflict with any such
 139         device created by systemd-networkd (or other tools). Ideally there
 140         would be a kernel compile-time option for this, but there currently
 141         isn't. The next best thing is to make this change through a modprobe.d
 142         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 143
 144         Required for systemd-nspawn:
 145           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 146
 147         Required for systemd-oomd:
 148           CONFIG_PSI
 149
 150         Note that kernel auditing is broken when used with systemd's
 151         container code. When using systemd in conjunction with
 152         containers, please make sure to either turn off auditing at
 153         runtime using the kernel command line option "audit=0", or
 154         turn it off at kernel compile time using:
 155           CONFIG_AUDIT=n
 156         If systemd is compiled with libseccomp support on
 157         architectures which do not use socketcall() and where seccomp
 158         is supported (this effectively means x86-64 and ARM, but
 159         excludes 32-bit x86!), then nspawn will now install a
 160         work-around seccomp filter that makes containers boot even
 161         with audit being enabled. This works correctly only on kernels
 162         3.14 and newer though. TL;DR: turn audit off, still.
 163
 164         glibc >= 2.16
 165         libcap
 166         libmount >= 2.30 (from util-linux)
 167                 (util-linux *must* be built without --enable-libmount-support-mtab)
 168         libseccomp >= 2.3.1 (optional)
 169         libblkid >= 2.24 (from util-linux) (optional)
 170         libkmod >= 15 (optional)
 171         PAM >= 1.1.2 (optional)
 172         libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
 173         libaudit (optional)
 174         libacl (optional)
 175         libbpf >= 0.2.0 (optional)
 176         libfdisk >= 2.33 (from util-linux) (optional)
 177         libselinux (optional)
 178         liblzma (optional)
 179         liblz4 >= 1.3.0 / 130 (optional)
 180         libzstd >= 1.4.0 (optional)
 181         libgcrypt (optional)
 182         libqrencode (optional)
 183         libmicrohttpd (optional)
 184         libpython (optional)
 185         libidn2 or libidn (optional)
 186         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 187         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 188         elfutils >= 158 (optional)
 189         polkit (optional)
 190         tzdata >= 2014f (optional)
 191         pkg-config
 192         gperf
 193         docbook-xsl (optional, required for documentation)
 194         xsltproc    (optional, required for documentation)
 195         python-jinja2
 196         python-lxml (optional, required to build the indices)
 197         python >= 3.5
 198         meson >= 0.47 (>= 0.49 is required to build position-independent executables)
 199         ninja
 200         gcc, awk, sed, grep, and similar tools
 201         clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
 202                 from source code in C)
 203
 204         During runtime, you need the following additional
 205         dependencies:
 206
 207         util-linux >= v2.27.1 required
 208         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 209                 NOTE: If using dbus < 1.9.18, you should override the default
 210                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 211         dracut (optional)
 212         polkit (optional)
 213
 214         To build in directory build/:
 215           meson setup build/ && meson compile -C build/
 216
 217         Any configuration options can be specified as -Darg=value... arguments
 218         to meson. After the build directory is initially configured, meson will
 219         refuse to run again, and options must be changed with:
 220           meson configure -Darg=value build/
 221         meson configure without any arguments will print out available options and
 222         their current values.
 223
 224         Useful commands:
 225           meson compile -v -C build/ some/target
 226           meson test -C build/
 227           sudo meson install -C build/
 228           DESTDIR=... meson install -C build/
 229
 230         A tarball can be created with:
 231           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 232
 233         When systemd-hostnamed is used, it is strongly recommended to
 234         install nss-myhostname to ensure that, in a world of
 235         dynamically changing hostnames, the hostname stays resolvable
 236         under all circumstances. In fact, systemd-hostnamed will warn
 237         if nss-myhostname is not installed.
 238
 239         nss-systemd must be enabled on systemd systems, as that's required for
 240         DynamicUser= to work. Note that we ship services out-of-the-box that
 241         make use of DynamicUser= now, hence enabling nss-systemd is not
 242         optional.
 243
 244         Note that the build prefix for systemd must be /usr. (Moreover,
 245         packages systemd relies on — such as D-Bus — really should use the same
 246         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 247         default and does not need to be specified) is the recommended setting.
 248         -Dsplit-usr=true can be used to give a semblance of support for systems
 249         with programs installed split between / and /usr. Moving everything
 250         under /usr is strongly encouraged.
 251
 252         Additional packages are necessary to run some tests:
 253         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 254         - nc                 (used by test/TEST-12-ISSUE-3171)
 255         - python3-pyparsing
 256         - python3-evdev      (used by hwdb parsing tests)
 257         - strace             (used by test/test-functions)
 258         - capsh              (optional, used by test-execute)
 259
 260 USERS AND GROUPS:
 261         Default udev rules use the following standard system group
 262         names, which need to be resolvable by getgrnam() at any time,
 263         even in the very early boot stages, where no other databases
 264         and network are available:
 265
 266         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 267
 268         During runtime, the journal daemon requires the
 269         "systemd-journal" system group to exist. New journal files will
 270         be readable by this group (but not writable), which may be used
 271         to grant specific users read access. In addition, system
 272         groups "wheel" and "adm" will be given read-only access to
 273         journal files using systemd-tmpfiles.service.
 274
 275         The journal remote daemon requires the
 276         "systemd-journal-remote" system user and group to
 277         exist. During execution this network facing service will drop
 278         privileges and assume this uid/gid for security reasons.
 279
 280         Similarly, the network management daemon requires the
 281         "systemd-network" system user and group to exist.
 282
 283         Similarly, the name resolution daemon requires the
 284         "systemd-resolve" system user and group to exist.
 285
 286         Similarly, the coredump support requires the
 287         "systemd-coredump" system user and group to exist.
 288
 289 NSS:
 290         systemd ships with four glibc NSS modules:
 291
 292         nss-myhostname resolves the local hostname to locally configured IP
 293         addresses, as well as "localhost" to 127.0.0.1/::1.
 294
 295         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 296         caching stub resolver "systemd-resolved".
 297
 298         nss-mymachines enables resolution of all local containers registered
 299         with machined to their respective IP addresses.
 300
 301         nss-systemd enables resolution of users/group registered via the
 302         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 303         including all dynamically allocated service users. (See the
 304         DynamicUser= setting in unit files.)
 305
 306         To make use of these NSS modules, please add them to the "hosts:",
 307         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 308         module should replace the glibc "dns" module in this file (and don't
 309         worry, it chain-loads the "dns" module if it can't talk to resolved).
 310
 311         The four modules should be used in the following order:
 312
 313                 passwd: compat systemd
 314                 group: compat systemd
 315                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 316
 317 SYSV INIT.D SCRIPTS:
 318         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 319         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 320         this needs to translate the action into the distribution specific
 321         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 322         this script if you need this functionality (you don't if you disabled
 323         SysV init support).
 324
 325         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 326         needs to look like, and provide an implementation at the marked places.
 327
 328 WARNINGS:
 329         systemd will warn during early boot if /usr is not already mounted at
 330         this point (that means: either located on the same file system as / or
 331         already mounted in the initrd). While in systemd itself very little
 332         will break if /usr is on a separate, late-mounted partition, many of
 333         its dependencies very likely will break sooner or later in one form or
 334         another. For example, udev rules tend to refer to binaries in /usr,
 335         binaries that link to libraries in /usr or binaries that refer to data
 336         files in /usr. Since these breakages are not always directly visible,
 337         systemd will warn about this, since this kind of file system setup is
 338         not really supported anymore by the basic set of Linux OS components.
 339
 340         systemd requires that the /run mount point exists. systemd also
 341         requires that /var/run is a symlink to /run.
 342
 343         For more information on this issue consult
 344         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 345
 346         To run systemd under valgrind, compile with meson option
 347         -Dvalgrind=true and have valgrind development headers installed
 348         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 349         triggered by code which violates some rules but is actually safe. Note
 350         that valgrind generates nice output only on exit(), hence on shutdown
 351         we don't execve() systemd-shutdown.
 352
 353 STABLE BRANCHES AND BACKPORTS:
 354         Stable branches with backported patches are available in the
 355         systemd-stable repo at https://github.com/systemd/systemd-stable.
 356
 357         Stable branches are started for certain releases of systemd and named
 358         after them, e.g. v238-stable. Stable branches are managed by
 359         distribution maintainers on an as needed basis. See
 360         https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 361         more information and examples.