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