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         libgcrypt (optional)
 154         libqrencode (optional)
 155         libmicrohttpd (optional)
 156         libpython (optional)
 157         libidn2 or libidn (optional)
 158         gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
 159         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 160         elfutils >= 158 (optional)
 161         polkit (optional)
 162         tzdata >= 2014f (optional)
 163         pkg-config
 164         gperf
 165         docbook-xsl (optional, required for documentation)
 166         xsltproc    (optional, required for documentation)
 167         python-lxml (optional, required to build the indices)
 168         python >= 3.5
 169         meson >= 0.46 (>= 0.49 is required to build position-independent executables)
 170         ninja
 171         gcc, awk, sed, grep, m4, and similar tools
 172
 173         During runtime, you need the following additional
 174         dependencies:
 175
 176         util-linux >= v2.27.1 required
 177         dbus >= 1.11.0 (strictly speaking optional, but recommended)
 178         dracut (optional)
 179         polkit (optional)
 180
 181         To build in directory build/:
 182           meson build/ && ninja -C build
 183
 184         Any configuration options can be specified as -Darg=value... arguments
 185         to meson. After the build directory is initially configured, meson will
 186         refuse to run again, and options must be changed with:
 187           mesonconf -Darg=value...
 188         mesonconf without any arguments will print out available options and
 189         their current values.
 190
 191         Useful commands:
 192           ninja -v some/target
 193           ninja test
 194           sudo ninja install
 195           DESTDIR=... ninja install
 196
 197         A tarball can be created with:
 198           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 199
 200         When systemd-hostnamed is used, it is strongly recommended to
 201         install nss-myhostname to ensure that, in a world of
 202         dynamically changing hostnames, the hostname stays resolvable
 203         under all circumstances. In fact, systemd-hostnamed will warn
 204         if nss-myhostname is not installed.
 205
 206         nss-systemd must be enabled on systemd systems, as that's required for
 207         DynamicUser= to work. Note that we ship services out-of-the-box that
 208         make use of DynamicUser= now, hence enabling nss-systemd is not
 209         optional.
 210
 211         Note that the build prefix for systemd must be /usr. (Moreover,
 212         packages systemd relies on — such as D-Bus — really should use the same
 213         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 214         default and does not need to be specified) is the recommended setting,
 215         and -Dsplit-usr=true should be used on systems which have /usr on a
 216         separate partition.
 217
 218         Additional packages are necessary to run some tests:
 219         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 220         - nc                 (used by test/TEST-12-ISSUE-3171)
 221         - python3-pyparsing
 222         - python3-evdev      (used by hwdb parsing tests)
 223         - strace             (used by test/test-functions)
 224         - capsh              (optional, used by test-execute)
 225
 226 USERS AND GROUPS:
 227         Default udev rules use the following standard system group
 228         names, which need to be resolvable by getgrnam() at any time,
 229         even in the very early boot stages, where no other databases
 230         and network are available:
 231
 232         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 233
 234         During runtime, the journal daemon requires the
 235         "systemd-journal" system group to exist. New journal files will
 236         be readable by this group (but not writable), which may be used
 237         to grant specific users read access. In addition, system
 238         groups "wheel" and "adm" will be given read-only access to
 239         journal files using systemd-tmpfiles.service.
 240
 241         The journal remote daemon requires the
 242         "systemd-journal-remote" system user and group to
 243         exist. During execution this network facing service will drop
 244         privileges and assume this uid/gid for security reasons.
 245
 246         Similarly, the network management daemon requires the
 247         "systemd-network" system user and group to exist.
 248
 249         Similarly, the name resolution daemon requires the
 250         "systemd-resolve" system user and group to exist.
 251
 252         Similarly, the coredump support requires the
 253         "systemd-coredump" system user and group to exist.
 254
 255 NSS:
 256         systemd ships with four glibc NSS modules:
 257
 258         nss-myhostname resolves the local hostname to locally
 259         configured IP addresses, as well as "localhost" to
 260         127.0.0.1/::1.
 261
 262         nss-resolve enables DNS resolution via the systemd-resolved
 263         DNS/LLMNR caching stub resolver "systemd-resolved".
 264
 265         nss-mymachines enables resolution of all local containers registered
 266         with machined to their respective IP addresses. It also maps UID/GIDs
 267         ranges used by containers to useful names.
 268
 269         nss-systemd enables resolution of all dynamically allocated service
 270         users. (See the DynamicUser= setting in unit files.)
 271
 272         To make use of these NSS modules, please add them to the "hosts:",
 273         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 274         module should replace the glibc "dns" module in this file (and don't
 275         worry, it chain-loads the "dns" module if it can't talk to resolved).
 276
 277         The four modules should be used in the following order:
 278
 279                 passwd: compat mymachines systemd
 280                 group: compat mymachines systemd
 281                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 282
 283 SYSV INIT.D SCRIPTS:
 284         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 285         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 286         this needs to translate the action into the distribution specific
 287         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 288         this script if you need this functionality (you don't if you disabled
 289         SysV init support).
 290
 291         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 292         needs to look like, and provide an implementation at the marked places.
 293
 294 WARNINGS:
 295         systemd will warn during early boot if /usr is not already mounted at
 296         this point (that means: either located on the same file system as / or
 297         already mounted in the initrd). While in systemd itself very little
 298         will break if /usr is on a separate, late-mounted partition, many of
 299         its dependencies very likely will break sooner or later in one form or
 300         another. For example, udev rules tend to refer to binaries in /usr,
 301         binaries that link to libraries in /usr or binaries that refer to data
 302         files in /usr. Since these breakages are not always directly visible,
 303         systemd will warn about this, since this kind of file system setup is
 304         not really supported anymore by the basic set of Linux OS components.
 305
 306         systemd requires that the /run mount point exists. systemd also
 307         requires that /var/run is a symlink to /run.
 308
 309         For more information on this issue consult
 310         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 311
 312         To run systemd under valgrind, compile with meson option
 313         -Dvalgrind=true and have valgrind development headers installed
 314         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 315         triggered by code which violates some rules but is actually safe. Note
 316         that valgrind generates nice output only on exit(), hence on shutdown
 317         we don't execve() systemd-shutdown.
 318
 319 STABLE BRANCHES AND BACKPORTS:
 320        Stable branches with backported patches are available in the
 321        systemd-stable repo at https://github.com/systemd/systemd-stable.
 322
 323        Stable branches are started for certain releases of systemd and named
 324        after them, e.g. v238-stable. Stable branches are managed by
 325        distribution maintainers on an as needed basis. See
 326        https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 327        more information and examples.
 328
 329 ENGINEERING AND CONSULTING SERVICES:
 330         Kinvolk (https://kinvolk.io) offers professional engineering
 331         and consulting services for systemd. Please contact Chris Kühl
 332         <chris@kinvolk.io> for more information.