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
  39         Kernel Config Options:
  40           CONFIG_DEVTMPFS
  41           CONFIG_CGROUPS (it is OK to disable all controllers)
  42           CONFIG_INOTIFY_USER
  43           CONFIG_SIGNALFD
  44           CONFIG_TIMERFD
  45           CONFIG_EPOLL
  46           CONFIG_NET
  47           CONFIG_SYSFS
  48           CONFIG_PROC_FS
  49           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  50
  51         Kernel crypto/hash API
  52           CONFIG_CRYPTO_USER_API_HASH
  53           CONFIG_CRYPTO_HMAC
  54           CONFIG_CRYPTO_SHA256
  55
  56         udev will fail to work with the legacy sysfs layout:
  57           CONFIG_SYSFS_DEPRECATED=n
  58
  59         Legacy hotplug slows down the system and confuses udev:
  60           CONFIG_UEVENT_HELPER_PATH=""
  61
  62         Userspace firmware loading is not supported and should
  63         be disabled in the kernel:
  64           CONFIG_FW_LOADER_USER_HELPER=n
  65
  66         Some udev rules and virtualization detection relies on it:
  67           CONFIG_DMIID
  68
  69         Support for some SCSI devices serial number retrieval, to
  70         create additional symlinks in /dev/disk/ and /dev/tape:
  71           CONFIG_BLK_DEV_BSG
  72
  73         Required for PrivateNetwork= in service units:
  74           CONFIG_NET_NS
  75         Note that systemd-localed.service and other systemd units use
  76         PrivateNetwork so this is effectively required.
  77
  78         Required for PrivateUsers= in service units:
  79           CONFIG_USER_NS
  80
  81         Optional but strongly recommended:
  82           CONFIG_IPV6
  83           CONFIG_AUTOFS4_FS
  84           CONFIG_TMPFS_XATTR
  85           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  86           CONFIG_SECCOMP
  87           CONFIG_SECCOMP_FILTER (required for seccomp support)
  88           CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
  89
  90         Required for CPUShares= in resource control unit settings
  91           CONFIG_CGROUP_SCHED
  92           CONFIG_FAIR_GROUP_SCHED
  93
  94         Required for CPUQuota= in resource control unit settings
  95           CONFIG_CFS_BANDWIDTH
  96
  97         Required for IPAddressDeny= and IPAddressAllow= in resource control
  98         unit settings
  99           CONFIG_CGROUP_BPF
 100
 101         For UEFI systems:
 102           CONFIG_EFIVAR_FS
 103           CONFIG_EFI_PARTITION
 104
 105         We recommend to turn off Real-Time group scheduling in the
 106         kernel when using systemd. RT group scheduling effectively
 107         makes RT scheduling unavailable for most userspace, since it
 108         requires explicit assignment of RT budgets to each unit whose
 109         processes making use of RT. As there's no sensible way to
 110         assign these budgets automatically this cannot really be
 111         fixed, and it's best to disable group scheduling hence.
 112            CONFIG_RT_GROUP_SCHED=n
 113
 114         It's a good idea to disable the implicit creation of networking bonding
 115         devices by the kernel networking bonding module, so that the
 116         automatically created "bond0" interface doesn't conflict with any such
 117         device created by systemd-networkd (or other tools). Ideally there
 118         would be a kernel compile-time option for this, but there currently
 119         isn't. The next best thing is to make this change through a modprobe.d
 120         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 121
 122         Required for systemd-nspawn:
 123           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 124
 125         Note that kernel auditing is broken when used with systemd's
 126         container code. When using systemd in conjunction with
 127         containers, please make sure to either turn off auditing at
 128         runtime using the kernel command line option "audit=0", or
 129         turn it off at kernel compile time using:
 130           CONFIG_AUDIT=n
 131         If systemd is compiled with libseccomp support on
 132         architectures which do not use socketcall() and where seccomp
 133         is supported (this effectively means x86-64 and ARM, but
 134         excludes 32-bit x86!), then nspawn will now install a
 135         work-around seccomp filter that makes containers boot even
 136         with audit being enabled. This works correctly only on kernels
 137         3.14 and newer though. TL;DR: turn audit off, still.
 138
 139         glibc >= 2.16
 140         libcap
 141         libmount >= 2.30 (from util-linux)
 142                 (util-linux *must* be built without --enable-libmount-support-mtab)
 143         libseccomp >= 2.3.1 (optional)
 144         libblkid >= 2.24 (from util-linux) (optional)
 145         libkmod >= 15 (optional)
 146         PAM >= 1.1.2 (optional)
 147         libcryptsetup (optional)
 148         libaudit (optional)
 149         libacl (optional)
 150         libselinux (optional)
 151         liblzma (optional)
 152         liblz4 >= 1.3.0 / 130 (optional)
 153         libzstd >= 1.4.0 (optional)
 154         libgcrypt (optional)
 155         libqrencode (optional)
 156         libmicrohttpd (optional)
 157         libpython (optional)
 158         libidn2 or libidn (optional)
 159         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 160         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 161         elfutils >= 158 (optional)
 162         polkit (optional)
 163         tzdata >= 2014f (optional)
 164         pkg-config
 165         gperf
 166         docbook-xsl (optional, required for documentation)
 167         xsltproc    (optional, required for documentation)
 168         python-lxml (optional, required to build the indices)
 169         python >= 3.5
 170         meson >= 0.46 (>= 0.49 is required to build position-independent executables)
 171         ninja
 172         gcc, awk, sed, grep, m4, and similar tools
 173
 174         During runtime, you need the following additional
 175         dependencies:
 176
 177         util-linux >= v2.27.1 required
 178         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 179                 NOTE: If using dbus < 1.9.18, you should override the default
 180                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 181         dracut (optional)
 182         polkit (optional)
 183
 184         To build in directory build/:
 185           meson build/ && ninja -C build
 186
 187         Any configuration options can be specified as -Darg=value... arguments
 188         to meson. After the build directory is initially configured, meson will
 189         refuse to run again, and options must be changed with:
 190           mesonconf -Darg=value...
 191         mesonconf without any arguments will print out available options and
 192         their current values.
 193
 194         Useful commands:
 195           ninja -v some/target
 196           ninja test
 197           sudo ninja install
 198           DESTDIR=... ninja install
 199
 200         A tarball can be created with:
 201           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 202
 203         When systemd-hostnamed is used, it is strongly recommended to
 204         install nss-myhostname to ensure that, in a world of
 205         dynamically changing hostnames, the hostname stays resolvable
 206         under all circumstances. In fact, systemd-hostnamed will warn
 207         if nss-myhostname is not installed.
 208
 209         nss-systemd must be enabled on systemd systems, as that's required for
 210         DynamicUser= to work. Note that we ship services out-of-the-box that
 211         make use of DynamicUser= now, hence enabling nss-systemd is not
 212         optional.
 213
 214         Note that the build prefix for systemd must be /usr. (Moreover,
 215         packages systemd relies on — such as D-Bus — really should use the same
 216         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 217         default and does not need to be specified) is the recommended setting,
 218         and -Dsplit-usr=true should be used on systems which have /usr on a
 219         separate partition.
 220
 221         Additional packages are necessary to run some tests:
 222         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 223         - nc                 (used by test/TEST-12-ISSUE-3171)
 224         - python3-pyparsing
 225         - python3-evdev      (used by hwdb parsing tests)
 226         - strace             (used by test/test-functions)
 227         - capsh              (optional, used by test-execute)
 228
 229 USERS AND GROUPS:
 230         Default udev rules use the following standard system group
 231         names, which need to be resolvable by getgrnam() at any time,
 232         even in the very early boot stages, where no other databases
 233         and network are available:
 234
 235         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 236
 237         During runtime, the journal daemon requires the
 238         "systemd-journal" system group to exist. New journal files will
 239         be readable by this group (but not writable), which may be used
 240         to grant specific users read access. In addition, system
 241         groups "wheel" and "adm" will be given read-only access to
 242         journal files using systemd-tmpfiles.service.
 243
 244         The journal remote daemon requires the
 245         "systemd-journal-remote" system user and group to
 246         exist. During execution this network facing service will drop
 247         privileges and assume this uid/gid for security reasons.
 248
 249         Similarly, the network management daemon requires the
 250         "systemd-network" system user and group to exist.
 251
 252         Similarly, the name resolution daemon requires the
 253         "systemd-resolve" system user and group to exist.
 254
 255         Similarly, the coredump support requires the
 256         "systemd-coredump" system user and group to exist.
 257
 258 NSS:
 259         systemd ships with four glibc NSS modules:
 260
 261         nss-myhostname resolves the local hostname to locally
 262         configured IP addresses, as well as "localhost" to
 263         127.0.0.1/::1.
 264
 265         nss-resolve enables DNS resolution via the systemd-resolved
 266         DNS/LLMNR caching stub resolver "systemd-resolved".
 267
 268         nss-mymachines enables resolution of all local containers registered
 269         with machined to their respective IP addresses. It also maps UID/GIDs
 270         ranges used by containers to useful names.
 271
 272         nss-systemd enables resolution of all dynamically allocated service
 273         users. (See the DynamicUser= setting in unit files.)
 274
 275         To make use of these NSS modules, please add them to the "hosts:",
 276         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 277         module should replace the glibc "dns" module in this file (and don't
 278         worry, it chain-loads the "dns" module if it can't talk to resolved).
 279
 280         The four modules should be used in the following order:
 281
 282                 passwd: compat mymachines systemd
 283                 group: compat mymachines systemd
 284                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 285
 286 SYSV INIT.D SCRIPTS:
 287         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 288         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 289         this needs to translate the action into the distribution specific
 290         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 291         this script if you need this functionality (you don't if you disabled
 292         SysV init support).
 293
 294         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 295         needs to look like, and provide an implementation at the marked places.
 296
 297 WARNINGS:
 298         systemd will warn during early boot if /usr is not already mounted at
 299         this point (that means: either located on the same file system as / or
 300         already mounted in the initrd). While in systemd itself very little
 301         will break if /usr is on a separate, late-mounted partition, many of
 302         its dependencies very likely will break sooner or later in one form or
 303         another. For example, udev rules tend to refer to binaries in /usr,
 304         binaries that link to libraries in /usr or binaries that refer to data
 305         files in /usr. Since these breakages are not always directly visible,
 306         systemd will warn about this, since this kind of file system setup is
 307         not really supported anymore by the basic set of Linux OS components.
 308
 309         systemd requires that the /run mount point exists. systemd also
 310         requires that /var/run is a symlink to /run.
 311
 312         For more information on this issue consult
 313         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 314
 315         To run systemd under valgrind, compile with meson option
 316         -Dvalgrind=true and have valgrind development headers installed
 317         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 318         triggered by code which violates some rules but is actually safe. Note
 319         that valgrind generates nice output only on exit(), hence on shutdown
 320         we don't execve() systemd-shutdown.
 321
 322 STABLE BRANCHES AND BACKPORTS:
 323        Stable branches with backported patches are available in the
 324        systemd-stable repo at https://github.com/systemd/systemd-stable.
 325
 326        Stable branches are started for certain releases of systemd and named
 327        after them, e.g. v238-stable. Stable branches are managed by
 328        distribution maintainers on an as needed basis. See
 329        https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 330        more information and examples.
 331
 332 ENGINEERING AND CONSULTING SERVICES:
 333         Kinvolk (https://kinvolk.io) offers professional engineering
 334         and consulting services for systemd. Please contact Chris Kühl
 335         <chris@kinvolk.io> for more information.