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
  44         Kernel Config Options:
  45           CONFIG_DEVTMPFS
  46           CONFIG_CGROUPS (it is OK to disable all controllers)
  47           CONFIG_INOTIFY_USER
  48           CONFIG_SIGNALFD
  49           CONFIG_TIMERFD
  50           CONFIG_EPOLL
  51           CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
  52           CONFIG_SYSFS
  53           CONFIG_PROC_FS
  54           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  55
  56         Kernel crypto/hash API
  57           CONFIG_CRYPTO_USER_API_HASH
  58           CONFIG_CRYPTO_HMAC
  59           CONFIG_CRYPTO_SHA256
  60
  61         udev will fail to work with the legacy sysfs layout:
  62           CONFIG_SYSFS_DEPRECATED=n
  63
  64         Legacy hotplug slows down the system and confuses udev:
  65           CONFIG_UEVENT_HELPER_PATH=""
  66
  67         Userspace firmware loading is not supported and should
  68         be disabled in the kernel:
  69           CONFIG_FW_LOADER_USER_HELPER=n
  70
  71         Some udev rules and virtualization detection relies on it:
  72           CONFIG_DMIID
  73
  74         Support for some SCSI devices serial number retrieval, to
  75         create additional symlinks in /dev/disk/ and /dev/tape:
  76           CONFIG_BLK_DEV_BSG
  77
  78         Required for PrivateNetwork= in service units:
  79           CONFIG_NET_NS
  80         Note that systemd-localed.service and other systemd units use
  81         PrivateNetwork so this is effectively required.
  82
  83         Required for PrivateUsers= in service units:
  84           CONFIG_USER_NS
  85
  86         Optional but strongly recommended:
  87           CONFIG_IPV6
  88           CONFIG_AUTOFS_FS
  89           CONFIG_TMPFS_XATTR
  90           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  91           CONFIG_SECCOMP
  92           CONFIG_SECCOMP_FILTER (required for seccomp support)
  93           CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
  94
  95         Required for CPUShares= in resource control unit settings
  96           CONFIG_CGROUP_SCHED
  97           CONFIG_FAIR_GROUP_SCHED
  98
  99         Required for CPUQuota= in resource control unit settings
 100           CONFIG_CFS_BANDWIDTH
 101
 102         Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
 103         IPEgressFilterPath= in resource control unit settings
 104         unit settings
 105           CONFIG_BPF
 106           CONFIG_BPF_SYSCALL
 107           CONFIG_BPF_JIT
 108           CONFIG_HAVE_EBPF_JIT
 109           CONFIG_CGROUP_BPF
 110
 111         Required for SocketBind{Allow|Deny}= in resource control unit settings
 112           CONFIG_BPF
 113           CONFIG_BPF_SYSCALL
 114           CONFIG_BPF_JIT
 115           CONFIG_HAVE_EBPF_JIT
 116           CONFIG_CGROUP_BPF
 117
 118         For UEFI systems:
 119           CONFIG_EFIVAR_FS
 120           CONFIG_EFI_PARTITION
 121
 122         Required for signed Verity images support:
 123           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 124
 125         We recommend to turn off Real-Time group scheduling in the
 126         kernel when using systemd. RT group scheduling effectively
 127         makes RT scheduling unavailable for most userspace, since it
 128         requires explicit assignment of RT budgets to each unit whose
 129         processes making use of RT. As there's no sensible way to
 130         assign these budgets automatically this cannot really be
 131         fixed, and it's best to disable group scheduling hence.
 132            CONFIG_RT_GROUP_SCHED=n
 133
 134         It's a good idea to disable the implicit creation of networking bonding
 135         devices by the kernel networking bonding module, so that the
 136         automatically created "bond0" interface doesn't conflict with any such
 137         device created by systemd-networkd (or other tools). Ideally there
 138         would be a kernel compile-time option for this, but there currently
 139         isn't. The next best thing is to make this change through a modprobe.d
 140         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 141
 142         Required for systemd-nspawn:
 143           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 144
 145         Required for systemd-oomd:
 146           CONFIG_PSI
 147
 148         Note that kernel auditing is broken when used with systemd's
 149         container code. When using systemd in conjunction with
 150         containers, please make sure to either turn off auditing at
 151         runtime using the kernel command line option "audit=0", or
 152         turn it off at kernel compile time using:
 153           CONFIG_AUDIT=n
 154         If systemd is compiled with libseccomp support on
 155         architectures which do not use socketcall() and where seccomp
 156         is supported (this effectively means x86-64 and ARM, but
 157         excludes 32-bit x86!), then nspawn will now install a
 158         work-around seccomp filter that makes containers boot even
 159         with audit being enabled. This works correctly only on kernels
 160         3.14 and newer though. TL;DR: turn audit off, still.
 161
 162         glibc >= 2.16
 163         libcap
 164         libmount >= 2.30 (from util-linux)
 165                 (util-linux *must* be built without --enable-libmount-support-mtab)
 166         libseccomp >= 2.3.1 (optional)
 167         libblkid >= 2.24 (from util-linux) (optional)
 168         libkmod >= 15 (optional)
 169         PAM >= 1.1.2 (optional)
 170         libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
 171         libaudit (optional)
 172         libacl (optional)
 173         libbpf >= 0.2.0 (optional)
 174         libfdisk >= 2.33 (from util-linux) (optional)
 175         libselinux (optional)
 176         liblzma (optional)
 177         liblz4 >= 1.3.0 / 130 (optional)
 178         libzstd >= 1.4.0 (optional)
 179         libgcrypt (optional)
 180         libqrencode (optional)
 181         libmicrohttpd (optional)
 182         libpython (optional)
 183         libidn2 or libidn (optional)
 184         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 185         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 186         elfutils >= 158 (optional)
 187         polkit (optional)
 188         tzdata >= 2014f (optional)
 189         pkg-config
 190         gperf
 191         docbook-xsl (optional, required for documentation)
 192         xsltproc    (optional, required for documentation)
 193         python-jinja2
 194         python-lxml (optional, required to build the indices)
 195         python >= 3.5
 196         meson >= 0.46 (>= 0.49 is required to build position-independent executables)
 197         ninja
 198         gcc, awk, sed, grep, and similar tools
 199         clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
 200                 from source code in C)
 201
 202         During runtime, you need the following additional
 203         dependencies:
 204
 205         util-linux >= v2.27.1 required
 206         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 207                 NOTE: If using dbus < 1.9.18, you should override the default
 208                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 209         dracut (optional)
 210         polkit (optional)
 211
 212         To build in directory build/:
 213           meson setup build/ && meson compile -C build/
 214
 215         Any configuration options can be specified as -Darg=value... arguments
 216         to meson. After the build directory is initially configured, meson will
 217         refuse to run again, and options must be changed with:
 218           meson configure -Darg=value build/
 219         meson configure without any arguments will print out available options and
 220         their current values.
 221
 222         Useful commands:
 223           meson compile -v -C build/ some/target
 224           meson test -C build/
 225           sudo meson install -C build/
 226           DESTDIR=... meson install -C build/
 227
 228         A tarball can be created with:
 229           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 230
 231         When systemd-hostnamed is used, it is strongly recommended to
 232         install nss-myhostname to ensure that, in a world of
 233         dynamically changing hostnames, the hostname stays resolvable
 234         under all circumstances. In fact, systemd-hostnamed will warn
 235         if nss-myhostname is not installed.
 236
 237         nss-systemd must be enabled on systemd systems, as that's required for
 238         DynamicUser= to work. Note that we ship services out-of-the-box that
 239         make use of DynamicUser= now, hence enabling nss-systemd is not
 240         optional.
 241
 242         Note that the build prefix for systemd must be /usr. (Moreover,
 243         packages systemd relies on — such as D-Bus — really should use the same
 244         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 245         default and does not need to be specified) is the recommended setting.
 246         -Dsplit-usr=true can be used to give a semblance of support for systems
 247         with programs installed split between / and /usr. Moving everything
 248         under /usr is strongly encouraged.
 249
 250         Additional packages are necessary to run some tests:
 251         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 252         - nc                 (used by test/TEST-12-ISSUE-3171)
 253         - python3-pyparsing
 254         - python3-evdev      (used by hwdb parsing tests)
 255         - strace             (used by test/test-functions)
 256         - capsh              (optional, used by test-execute)
 257
 258 USERS AND GROUPS:
 259         Default udev rules use the following standard system group
 260         names, which need to be resolvable by getgrnam() at any time,
 261         even in the very early boot stages, where no other databases
 262         and network are available:
 263
 264         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 265
 266         During runtime, the journal daemon requires the
 267         "systemd-journal" system group to exist. New journal files will
 268         be readable by this group (but not writable), which may be used
 269         to grant specific users read access. In addition, system
 270         groups "wheel" and "adm" will be given read-only access to
 271         journal files using systemd-tmpfiles.service.
 272
 273         The journal remote daemon requires the
 274         "systemd-journal-remote" system user and group to
 275         exist. During execution this network facing service will drop
 276         privileges and assume this uid/gid for security reasons.
 277
 278         Similarly, the network management daemon requires the
 279         "systemd-network" system user and group to exist.
 280
 281         Similarly, the name resolution daemon requires the
 282         "systemd-resolve" system user and group to exist.
 283
 284         Similarly, the coredump support requires the
 285         "systemd-coredump" system user and group to exist.
 286
 287 NSS:
 288         systemd ships with four glibc NSS modules:
 289
 290         nss-myhostname resolves the local hostname to locally configured IP
 291         addresses, as well as "localhost" to 127.0.0.1/::1.
 292
 293         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 294         caching stub resolver "systemd-resolved".
 295
 296         nss-mymachines enables resolution of all local containers registered
 297         with machined to their respective IP addresses.
 298
 299         nss-systemd enables resolution of users/group registered via the
 300         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 301         including all dynamically allocated service users. (See the
 302         DynamicUser= setting in unit files.)
 303
 304         To make use of these NSS modules, please add them to the "hosts:",
 305         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 306         module should replace the glibc "dns" module in this file (and don't
 307         worry, it chain-loads the "dns" module if it can't talk to resolved).
 308
 309         The four modules should be used in the following order:
 310
 311                 passwd: compat systemd
 312                 group: compat systemd
 313                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 314
 315 SYSV INIT.D SCRIPTS:
 316         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 317         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 318         this needs to translate the action into the distribution specific
 319         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 320         this script if you need this functionality (you don't if you disabled
 321         SysV init support).
 322
 323         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 324         needs to look like, and provide an implementation at the marked places.
 325
 326 WARNINGS:
 327         systemd will warn during early boot if /usr is not already mounted at
 328         this point (that means: either located on the same file system as / or
 329         already mounted in the initrd). While in systemd itself very little
 330         will break if /usr is on a separate, late-mounted partition, many of
 331         its dependencies very likely will break sooner or later in one form or
 332         another. For example, udev rules tend to refer to binaries in /usr,
 333         binaries that link to libraries in /usr or binaries that refer to data
 334         files in /usr. Since these breakages are not always directly visible,
 335         systemd will warn about this, since this kind of file system setup is
 336         not really supported anymore by the basic set of Linux OS components.
 337
 338         systemd requires that the /run mount point exists. systemd also
 339         requires that /var/run is a symlink to /run.
 340
 341         For more information on this issue consult
 342         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 343
 344         To run systemd under valgrind, compile with meson option
 345         -Dvalgrind=true and have valgrind development headers installed
 346         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 347         triggered by code which violates some rules but is actually safe. Note
 348         that valgrind generates nice output only on exit(), hence on shutdown
 349         we don't execve() systemd-shutdown.
 350
 351 STABLE BRANCHES AND BACKPORTS:
 352         Stable branches with backported patches are available in the
 353         systemd-stable repo at https://github.com/systemd/systemd-stable.
 354
 355         Stable branches are started for certain releases of systemd and named
 356         after them, e.g. v238-stable. Stable branches are managed by
 357         distribution maintainers on an as needed basis. See
 358         https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 359         more information and examples.