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
  34 REQUIREMENTS:
  35         Linux kernel >= 3.13
  36         Linux kernel >= 4.2 for unified cgroup hierarchy support
  37
  38         Kernel Config Options:
  39           CONFIG_DEVTMPFS
  40           CONFIG_CGROUPS (it is OK to disable all controllers)
  41           CONFIG_INOTIFY_USER
  42           CONFIG_SIGNALFD
  43           CONFIG_TIMERFD
  44           CONFIG_EPOLL
  45           CONFIG_NET
  46           CONFIG_SYSFS
  47           CONFIG_PROC_FS
  48           CONFIG_FHANDLE (libudev, mount and bind mount handling)
  49
  50         Kernel crypto/hash API
  51           CONFIG_CRYPTO_USER_API_HASH
  52           CONFIG_CRYPTO_HMAC
  53           CONFIG_CRYPTO_SHA256
  54
  55         udev will fail to work with the legacy sysfs layout:
  56           CONFIG_SYSFS_DEPRECATED=n
  57
  58         Legacy hotplug slows down the system and confuses udev:
  59           CONFIG_UEVENT_HELPER_PATH=""
  60
  61         Userspace firmware loading is not supported and should
  62         be disabled in the kernel:
  63           CONFIG_FW_LOADER_USER_HELPER=n
  64
  65         Some udev rules and virtualization detection relies on it:
  66           CONFIG_DMIID
  67
  68         Support for some SCSI devices serial number retrieval, to
  69         create additional symlinks in /dev/disk/ and /dev/tape:
  70           CONFIG_BLK_DEV_BSG
  71
  72         Required for PrivateNetwork= in service units:
  73           CONFIG_NET_NS
  74         Note that systemd-localed.service and other systemd units use
  75         PrivateNetwork so this is effectively required.
  76
  77         Required for PrivateUsers= in service units:
  78           CONFIG_USER_NS
  79
  80         Optional but strongly recommended:
  81           CONFIG_IPV6
  82           CONFIG_AUTOFS4_FS
  83           CONFIG_TMPFS_XATTR
  84           CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
  85           CONFIG_SECCOMP
  86           CONFIG_SECCOMP_FILTER (required for seccomp support)
  87           CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)
  88
  89         Required for CPUShares= in resource control unit settings
  90           CONFIG_CGROUP_SCHED
  91           CONFIG_FAIR_GROUP_SCHED
  92
  93         Required for CPUQuota= in resource control unit settings
  94           CONFIG_CFS_BANDWIDTH
  95
  96         Required for IPAddressDeny= and IPAddressAllow= in resource control
  97         unit settings
  98           CONFIG_CGROUP_BPF
  99
 100         For UEFI systems:
 101           CONFIG_EFIVAR_FS
 102           CONFIG_EFI_PARTITION
 103
 104         We recommend to turn off Real-Time group scheduling in the
 105         kernel when using systemd. RT group scheduling effectively
 106         makes RT scheduling unavailable for most userspace, since it
 107         requires explicit assignment of RT budgets to each unit whose
 108         processes making use of RT. As there's no sensible way to
 109         assign these budgets automatically this cannot really be
 110         fixed, and it's best to disable group scheduling hence.
 111            CONFIG_RT_GROUP_SCHED=n
 112
 113         It's a good idea to disable the implicit creation of networking bonding
 114         devices by the kernel networking bonding module, so that the
 115         automatically created "bond0" interface doesn't conflict with any such
 116         device created by systemd-networkd (or other tools). Ideally there
 117         would be a kernel compile-time option for this, but there currently
 118         isn't. The next best thing is to make this change through a modprobe.d
 119         drop-in. This is shipped by default, see modprobe.d/systemd.conf.
 120
 121         Required for systemd-nspawn:
 122           CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
 123
 124         Note that kernel auditing is broken when used with systemd's
 125         container code. When using systemd in conjunction with
 126         containers, please make sure to either turn off auditing at
 127         runtime using the kernel command line option "audit=0", or
 128         turn it off at kernel compile time using:
 129           CONFIG_AUDIT=n
 130         If systemd is compiled with libseccomp support on
 131         architectures which do not use socketcall() and where seccomp
 132         is supported (this effectively means x86-64 and ARM, but
 133         excludes 32-bit x86!), then nspawn will now install a
 134         work-around seccomp filter that makes containers boot even
 135         with audit being enabled. This works correctly only on kernels
 136         3.14 and newer though. TL;DR: turn audit off, still.
 137
 138         glibc >= 2.16
 139         libcap
 140         libmount >= 2.30 (from util-linux)
 141                 (util-linux *must* be built without --enable-libmount-support-mtab)
 142         libseccomp >= 2.3.1 (optional)
 143         libblkid >= 2.24 (from util-linux) (optional)
 144         libkmod >= 15 (optional)
 145         PAM >= 1.1.2 (optional)
 146         libcryptsetup (optional)
 147         libaudit (optional)
 148         libacl (optional)
 149         libselinux (optional)
 150         liblzma (optional)
 151         liblz4 >= 1.3.0 / 130 (optional)
 152         libgcrypt (optional)
 153         libqrencode (optional)
 154         libmicrohttpd (optional)
 155         libpython (optional)
 156         libidn2 or libidn (optional)
 157         gnutls >= 3.1.4 (optional, >= 3.5.3 is required to support DNS-over-TLS with gnutls)
 158         openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
 159         elfutils >= 158 (optional)
 160         polkit (optional)
 161         tzdata >= 2014f (optional)
 162         pkg-config
 163         gperf
 164         docbook-xsl (optional, required for documentation)
 165         xsltproc    (optional, required for documentation)
 166         python-lxml (optional, required to build the indices)
 167         python >= 3.5
 168         meson >= 0.46 (>= 0.49 is required to build position-independent executables)
 169         ninja
 170         gcc, awk, sed, grep, m4, and similar tools
 171
 172         During runtime, you need the following additional
 173         dependencies:
 174
 175         util-linux >= v2.27.1 required
 176         dbus >= 1.11.0 (strictly speaking optional, but recommended)
 177         dracut (optional)
 178         polkit (optional)
 179
 180         To build in directory build/:
 181           meson build/ && ninja -C build
 182
 183         Any configuration options can be specified as -Darg=value... arguments
 184         to meson. After the build directory is initially configured, meson will
 185         refuse to run again, and options must be changed with:
 186           mesonconf -Darg=value...
 187         mesonconf without any arguments will print out available options and
 188         their current values.
 189
 190         Useful commands:
 191           ninja -v some/target
 192           ninja test
 193           sudo ninja install
 194           DESTDIR=... ninja install
 195
 196         A tarball can be created with:
 197           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 198
 199         When systemd-hostnamed is used, it is strongly recommended to
 200         install nss-myhostname to ensure that, in a world of
 201         dynamically changing hostnames, the hostname stays resolvable
 202         under all circumstances. In fact, systemd-hostnamed will warn
 203         if nss-myhostname is not installed.
 204
 205         nss-systemd must be enabled on systemd systems, as that's required for
 206         DynamicUser= to work. Note that we ship services out-of-the-box that
 207         make use of DynamicUser= now, hence enabling nss-systemd is not
 208         optional.
 209
 210         Note that the build prefix for systemd must be /usr. (Moreover,
 211         packages systemd relies on — such as D-Bus — really should use the same
 212         prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the
 213         default and does not need to be specified) is the recommended setting,
 214         and -Dsplit-usr=true should be used on systems which have /usr on a
 215         separate partition.
 216
 217         Additional packages are necessary to run some tests:
 218         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 219         - nc                 (used by test/TEST-12-ISSUE-3171)
 220         - python3-pyparsing
 221         - python3-evdev      (used by hwdb parsing tests)
 222         - strace             (used by test/test-functions)
 223         - capsh              (optional, used by test-execute)
 224
 225 USERS AND GROUPS:
 226         Default udev rules use the following standard system group
 227         names, which need to be resolvable by getgrnam() at any time,
 228         even in the very early boot stages, where no other databases
 229         and network are available:
 230
 231         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 232
 233         During runtime, the journal daemon requires the
 234         "systemd-journal" system group to exist. New journal files will
 235         be readable by this group (but not writable), which may be used
 236         to grant specific users read access. In addition, system
 237         groups "wheel" and "adm" will be given read-only access to
 238         journal files using systemd-tmpfiles.service.
 239
 240         The journal remote daemon requires the
 241         "systemd-journal-remote" system user and group to
 242         exist. During execution this network facing service will drop
 243         privileges and assume this uid/gid for security reasons.
 244
 245         Similarly, the network management daemon requires the
 246         "systemd-network" system user and group to exist.
 247
 248         Similarly, the name resolution daemon requires the
 249         "systemd-resolve" system user and group to exist.
 250
 251         Similarly, the coredump support requires the
 252         "systemd-coredump" system user and group to exist.
 253
 254 NSS:
 255         systemd ships with four glibc NSS modules:
 256
 257         nss-myhostname resolves the local hostname to locally
 258         configured IP addresses, as well as "localhost" to
 259         127.0.0.1/::1.
 260
 261         nss-resolve enables DNS resolution via the systemd-resolved
 262         DNS/LLMNR caching stub resolver "systemd-resolved".
 263
 264         nss-mymachines enables resolution of all local containers registered
 265         with machined to their respective IP addresses. It also maps UID/GIDs
 266         ranges used by containers to useful names.
 267
 268         nss-systemd enables resolution of all dynamically allocated service
 269         users. (See the DynamicUser= setting in unit files.)
 270
 271         To make use of these NSS modules, please add them to the "hosts:",
 272         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 273         module should replace the glibc "dns" module in this file (and don't
 274         worry, it chain-loads the "dns" module if it can't talk to resolved).
 275
 276         The four modules should be used in the following order:
 277
 278                 passwd: compat mymachines systemd
 279                 group: compat mymachines systemd
 280                 hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
 281
 282 SYSV INIT.D SCRIPTS:
 283         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 284         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 285         this needs to translate the action into the distribution specific
 286         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 287         this script if you need this functionality (you don't if you disabled
 288         SysV init support).
 289
 290         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 291         needs to look like, and provide an implementation at the marked places.
 292
 293 WARNINGS:
 294         systemd will warn during early boot if /usr is not already mounted at
 295         this point (that means: either located on the same file system as / or
 296         already mounted in the initrd). While in systemd itself very little
 297         will break if /usr is on a separate, late-mounted partition, many of
 298         its dependencies very likely will break sooner or later in one form or
 299         another. For example, udev rules tend to refer to binaries in /usr,
 300         binaries that link to libraries in /usr or binaries that refer to data
 301         files in /usr. Since these breakages are not always directly visible,
 302         systemd will warn about this, since this kind of file system setup is
 303         not really supported anymore by the basic set of Linux OS components.
 304
 305         systemd requires that the /run mount point exists. systemd also
 306         requires that /var/run is a symlink to /run.
 307
 308         For more information on this issue consult
 309         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 310
 311         To run systemd under valgrind, compile with meson option
 312         -Dvalgrind=true and have valgrind development headers installed
 313         (i.e. valgrind-devel or equivalent). Otherwise, false positives will be
 314         triggered by code which violates some rules but is actually safe. Note
 315         that valgrind generates nice output only on exit(), hence on shutdown
 316         we don't execve() systemd-shutdown.
 317
 318 STABLE BRANCHES AND BACKPORTS:
 319        Stable branches with backported patches are available in the
 320        systemd-stable repo at https://github.com/systemd/systemd-stable.
 321
 322        Stable branches are started for certain releases of systemd and named
 323        after them, e.g. v238-stable. Stable branches are managed by
 324        distribution maintainers on an as needed basis. See
 325        https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some
 326        more information and examples.
 327
 328 ENGINEERING AND CONSULTING SERVICES:
 329         Kinvolk (https://kinvolk.io) offers professional engineering
 330         and consulting services for systemd. Please contact Chris Kühl
 331         <chris@kinvolk.io> for more information.