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