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.freenode.org
  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 >= 5.4 for signed Verity images support
  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_AUTOFS4_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= and IPAddressAllow= in resource control
  99         unit settings
 100           CONFIG_CGROUP_BPF
 101
 102         For UEFI systems:
 103           CONFIG_EFIVAR_FS
 104           CONFIG_EFI_PARTITION
 105
 106         Required for signed Verity images support:
 107           CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
 108
 109         We recommend to turn off Real-Time group scheduling in the
 110         kernel when using systemd. RT group scheduling effectively
 111         makes RT scheduling unavailable for most userspace, since it
 112         requires explicit assignment of RT budgets to each unit whose
 113         processes making use of RT. As there's no sensible way to
 114         assign these budgets automatically this cannot really be
 115         fixed, and it's best to disable group scheduling hence.
 116            CONFIG_RT_GROUP_SCHED=n
 117
 118         It's a good idea to disable the implicit creation of networking bonding
 119         devices by the kernel networking bonding module, so that the
 120         automatically created "bond0" interface doesn't conflict with any such
 121         device created by systemd-networkd (or other tools). Ideally there
 122         would be a kernel compile-time option for this, but there currently
 123         isn't. The next best thing is to make this change through a modprobe.d
 124         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 125
 126         Required for systemd-nspawn:
 127           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 128
 129         Required for systemd-oomd:
 130           CONFIG_PSI
 131
 132         Note that kernel auditing is broken when used with systemd's
 133         container code. When using systemd in conjunction with
 134         containers, please make sure to either turn off auditing at
 135         runtime using the kernel command line option "audit=0", or
 136         turn it off at kernel compile time using:
 137           CONFIG_AUDIT=n
 138         If systemd is compiled with libseccomp support on
 139         architectures which do not use socketcall() and where seccomp
 140         is supported (this effectively means x86-64 and ARM, but
 141         excludes 32-bit x86!), then nspawn will now install a
 142         work-around seccomp filter that makes containers boot even
 143         with audit being enabled. This works correctly only on kernels
 144         3.14 and newer though. TL;DR: turn audit off, still.
 145
 146         glibc >= 2.16
 147         libcap
 148         libmount >= 2.30 (from util-linux)
 149                 (util-linux *must* be built without --enable-libmount-support-mtab)
 150         libseccomp >= 2.3.1 (optional)
 151         libblkid >= 2.24 (from util-linux) (optional)
 152         libkmod >= 15 (optional)
 153         PAM >= 1.1.2 (optional)
 154         libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
 155         libaudit (optional)
 156         libacl (optional)
 157         libfdisk >= 2.33 (from util-linux) (optional)
 158         libselinux (optional)
 159         liblzma (optional)
 160         liblz4 >= 1.3.0 / 130 (optional)
 161         libzstd >= 1.4.0 (optional)
 162         libgcrypt (optional)
 163         libqrencode (optional)
 164         libmicrohttpd (optional)
 165         libpython (optional)
 166         libidn2 or libidn (optional)
 167         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 168         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 169         elfutils >= 158 (optional)
 170         polkit (optional)
 171         tzdata >= 2014f (optional)
 172         pkg-config
 173         gperf
 174         docbook-xsl (optional, required for documentation)
 175         xsltproc    (optional, required for documentation)
 176         python-lxml (optional, required to build the indices)
 177         python >= 3.5
 178         meson >= 0.46 (>= 0.49 is required to build position-independent executables)
 179         ninja
 180         gcc, awk, sed, grep, m4, and similar tools
 181
 182         During runtime, you need the following additional
 183         dependencies:
 184
 185         util-linux >= v2.27.1 required
 186         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 187                 NOTE: If using dbus < 1.9.18, you should override the default
 188                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 189         dracut (optional)
 190         polkit (optional)
 191
 192         To build in directory build/:
 193           meson setup build/ && meson compile -C build/
 194
 195         Any configuration options can be specified as -Darg=value... arguments
 196         to meson. After the build directory is initially configured, meson will
 197         refuse to run again, and options must be changed with:
 198           meson configure -Darg=value build/
 199         meson configure without any arguments will print out available options and
 200         their current values.
 201
 202         Useful commands:
 203           meson compile -v -C build/ some/target
 204           meson test -C build/
 205           sudo meson install -C build/
 206           DESTDIR=... meson install -C build/
 207
 208         A tarball can be created with:
 209           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 210
 211         When systemd-hostnamed is used, it is strongly recommended to
 212         install nss-myhostname to ensure that, in a world of
 213         dynamically changing hostnames, the hostname stays resolvable
 214         under all circumstances. In fact, systemd-hostnamed will warn
 215         if nss-myhostname is not installed.
 216
 217         nss-systemd must be enabled on systemd systems, as that's required for
 218         DynamicUser= to work. Note that we ship services out-of-the-box that
 219         make use of DynamicUser= now, hence enabling nss-systemd is not
 220         optional.
 221
 222         Note that the build prefix for systemd must be /usr. (Moreover,
 223         packages systemd relies on — such as D-Bus — really should use the same
 224         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 225         default and does not need to be specified) is the recommended setting.
 226         -Dsplit-usr=true can be used to give a semblance of support for systems
 227         with programs installed split between / and /usr. Moving everything
 228         under /usr is strongly encouraged.
 229
 230         Additional packages are necessary to run some tests:
 231         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 232         - nc                 (used by test/TEST-12-ISSUE-3171)
 233         - python3-pyparsing
 234         - python3-evdev      (used by hwdb parsing tests)
 235         - strace             (used by test/test-functions)
 236         - capsh              (optional, used by test-execute)
 237
 238 USERS AND GROUPS:
 239         Default udev rules use the following standard system group
 240         names, which need to be resolvable by getgrnam() at any time,
 241         even in the very early boot stages, where no other databases
 242         and network are available:
 243
 244         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 245
 246         During runtime, the journal daemon requires the
 247         "systemd-journal" system group to exist. New journal files will
 248         be readable by this group (but not writable), which may be used
 249         to grant specific users read access. In addition, system
 250         groups "wheel" and "adm" will be given read-only access to
 251         journal files using systemd-tmpfiles.service.
 252
 253         The journal remote daemon requires the
 254         "systemd-journal-remote" system user and group to
 255         exist. During execution this network facing service will drop
 256         privileges and assume this uid/gid for security reasons.
 257
 258         Similarly, the network management daemon requires the
 259         "systemd-network" system user and group to exist.
 260
 261         Similarly, the name resolution daemon requires the
 262         "systemd-resolve" system user and group to exist.
 263
 264         Similarly, the coredump support requires the
 265         "systemd-coredump" system user and group to exist.
 266
 267 NSS:
 268         systemd ships with four glibc NSS modules:
 269
 270         nss-myhostname resolves the local hostname to locally configured IP
 271         addresses, as well as "localhost" to 127.0.0.1/::1.
 272
 273         nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
 274         caching stub resolver "systemd-resolved".
 275
 276         nss-mymachines enables resolution of all local containers registered
 277         with machined to their respective IP addresses.
 278
 279         nss-systemd enables resolution of users/group registered via the
 280         User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
 281         including all dynamically allocated service users. (See the
 282         DynamicUser= setting in unit files.)
 283
 284         To make use of these NSS modules, please add them to the "hosts:",
 285         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 286         module should replace the glibc "dns" module in this file (and don't
 287         worry, it chain-loads the "dns" module if it can't talk to resolved).
 288
 289         The four modules should be used in the following order:
 290
 291                 passwd: compat systemd
 292                 group: compat systemd
 293                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 294
 295 SYSV INIT.D SCRIPTS:
 296         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 297         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 298         this needs to translate the action into the distribution specific
 299         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 300         this script if you need this functionality (you don't if you disabled
 301         SysV init support).
 302
 303         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 304         needs to look like, and provide an implementation at the marked places.
 305
 306 WARNINGS:
 307         systemd will warn during early boot if /usr is not already mounted at
 308         this point (that means: either located on the same file system as / or
 309         already mounted in the initrd). While in systemd itself very little
 310         will break if /usr is on a separate, late-mounted partition, many of
 311         its dependencies very likely will break sooner or later in one form or
 312         another. For example, udev rules tend to refer to binaries in /usr,
 313         binaries that link to libraries in /usr or binaries that refer to data
 314         files in /usr. Since these breakages are not always directly visible,
 315         systemd will warn about this, since this kind of file system setup is
 316         not really supported anymore by the basic set of Linux OS components.
 317
 318         systemd requires that the /run mount point exists. systemd also
 319         requires that /var/run is a symlink to /run.
 320
 321         For more information on this issue consult
 322         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 323
 324         To run systemd under valgrind, compile with meson option
 325         -Dvalgrind=true and have valgrind development headers installed
 326         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 327         triggered by code which violates some rules but is actually safe. Note
 328         that valgrind generates nice output only on exit(), hence on shutdown
 329         we don't execve() systemd-shutdown.
 330
 331 STABLE BRANCHES AND BACKPORTS:
 332         Stable branches with backported patches are available in the
 333         systemd-stable repo at https://github.com/systemd/systemd-stable.
 334
 335         Stable branches are started for certain releases of systemd and named
 336         after them, e.g. v238-stable. Stable branches are managed by
 337         distribution maintainers on an as needed basis. See
 338         https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 339         more information and examples.
 340
 341 ENGINEERING AND CONSULTING SERVICES:
 342         Kinvolk (https://kinvolk.io) offers professional engineering
 343         and consulting services for systemd. Please contact Chris Kühl
 344         <chris@kinvolk.io> for more information.