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 >= 119 (optional)
 152         libgcrypt (optional)
 153         libqrencode (optional)
 154         libmicrohttpd (optional)
 155         libpython (optional)
 156         libidn2 or libidn (optional)
 157         elfutils >= 158 (optional)
 158         polkit (optional)
 159         pkg-config
 160         gperf
 161         docbook-xsl (optional, required for documentation)
 162         xsltproc    (optional, required for documentation)
 163         python-lxml (optional, required to build the indices)
 164         python, meson, ninja
 165         gcc, awk, sed, grep, m4, and similar tools
 166
 167         During runtime, you need the following additional
 168         dependencies:
 169
 170         util-linux >= v2.27.1 required
 171         dbus >= 1.4.0 (strictly speaking optional, but recommended)
 172                 NOTE: If using dbus < 1.9.18, you should override the default
 173                 policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
 174         dracut (optional)
 175         PolicyKit (optional)
 176
 177         To build in directory build/:
 178           meson build/ && ninja -C build
 179
 180         Any configuration options can be specfied as -Darg=value... arguments
 181         to meson. After the build directory is initially configured, meson will
 182         refuse to run again, and options must be changed with:
 183           mesonconf -Darg=value...
 184         mesonconf without any arguments will print out available options and
 185         their current values.
 186
 187         Useful commands:
 188           ninja -v some/target
 189           ninja test
 190           sudo ninja install
 191           DESTDIR=... ninja install
 192
 193         A tarball can be created with:
 194           git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz
 195
 196         When systemd-hostnamed is used, it is strongly recommended to
 197         install nss-myhostname to ensure that, in a world of
 198         dynamically changing hostnames, the hostname stays resolvable
 199         under all circumstances. In fact, systemd-hostnamed will warn
 200         if nss-myhostname is not installed.
 201
 202         nss-systemd must be enabled on systemd systems, as that's required for
 203         DynamicUser= to work. Note that we ship services out-of-the-box that
 204         make use of DynamicUser= now, hence enabling nss-systemd is not
 205         optional.
 206
 207         Note that the build prefix for systemd must be /usr. -Dsplit-usr=false
 208         (which is the default and does not need to be specified) is the
 209         recommended setting, and -Dsplit-usr=true should be used on systems
 210         which have /usr on a separate partition.
 211
 212         Additional packages are necessary to run some tests:
 213         - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
 214         - nc                 (used by test/TEST-12-ISSUE-3171)
 215         - python3-pyparsing
 216         - python3-evdev      (used by hwdb parsing tests)
 217         - strace             (used by test/test-functions)
 218         - capsh              (optional, used by test-execute)
 219
 220 USERS AND GROUPS:
 221         Default udev rules use the following standard system group
 222         names, which need to be resolvable by getgrnam() at any time,
 223         even in the very early boot stages, where no other databases
 224         and network are available:
 225
 226         audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
 227
 228         During runtime, the journal daemon requires the
 229         "systemd-journal" system group to exist. New journal files will
 230         be readable by this group (but not writable), which may be used
 231         to grant specific users read access. In addition, system
 232         groups "wheel" and "adm" will be given read-only access to
 233         journal files using systemd-tmpfiles.service.
 234
 235         The journal gateway daemon requires the
 236         "systemd-journal-gateway" system user and group to
 237         exist. During execution this network facing service will drop
 238         privileges and assume this uid/gid for security reasons.
 239
 240         Similarly, the NTP daemon requires the "systemd-timesync" system
 241         user and group to exist.
 242
 243         Similarly, the network management daemon requires the
 244         "systemd-network" system user and group to exist.
 245
 246         Similarly, the name resolution daemon requires the
 247         "systemd-resolve" system user and group to exist.
 248
 249         Similarly, the coredump support requires the
 250         "systemd-coredump" system user and group to exist.
 251
 252 NSS:
 253         systemd ships with four glibc NSS modules:
 254
 255         nss-myhostname resolves the local hostname to locally
 256         configured IP addresses, as well as "localhost" to
 257         127.0.0.1/::1.
 258
 259         nss-resolve enables DNS resolution via the systemd-resolved
 260         DNS/LLMNR caching stub resolver "systemd-resolved".
 261
 262         nss-mymachines enables resolution of all local containers registered
 263         with machined to their respective IP addresses. It also maps UID/GIDs
 264         ranges used by containers to useful names.
 265
 266         nss-systemd enables resolution of all dynamically allocated service
 267         users. (See the DynamicUser= setting in unit files.)
 268
 269         To make use of these NSS modules, please add them to the "hosts:",
 270         "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
 271         module should replace the glibc "dns" module in this file (and don't
 272         worry, it chain-loads the "dns" module if it can't talk to resolved).
 273
 274         The four modules should be used in the following order:
 275
 276                 passwd: compat mymachines systemd
 277                 group: compat mymachines systemd
 278                 hosts: files mymachines resolve myhostname
 279
 280 SYSV INIT.D SCRIPTS:
 281         When calling "systemctl enable/disable/is-enabled" on a unit which is a
 282         SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
 283         this needs to translate the action into the distribution specific
 284         mechanism such as chkconfig or update-rc.d. Packagers need to provide
 285         this script if you need this functionality (you don't if you disabled
 286         SysV init support).
 287
 288         Please see src/systemctl/systemd-sysv-install.SKELETON for how this
 289         needs to look like, and provide an implementation at the marked places.
 290
 291 WARNINGS:
 292         systemd will warn during early boot if /usr is not already mounted at
 293         this point (that means: either located on the same file system as / or
 294         already mounted in the initrd). While in systemd itself very little
 295         will break if /usr is on a separate, late-mounted partition, many of
 296         its dependencies very likely will break sooner or later in one form or
 297         another. For example, udev rules tend to refer to binaries in /usr,
 298         binaries that link to libraries in /usr or binaries that refer to data
 299         files in /usr. Since these breakages are not always directly visible,
 300         systemd will warn about this, since this kind of file system setup is
 301         not really supported anymore by the basic set of Linux OS components.
 302
 303         systemd requires that the /run mount point exists. systemd also
 304         requires that /var/run is a symlink to /run.
 305
 306         For more information on this issue consult
 307         https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
 308
 309         To run systemd under valgrind, compile with VALGRIND defined
 310         (e.g. CPPFLAGS='... -DVALGRIND=1' meson <options>) and have valgrind
 311         development headers installed (i.e. valgrind-devel or
 312         equivalent). Otherwise, false positives will be triggered by code which
 313         violates some rules but is actually safe. Note that valgrind generates
 314         nice output only on exit(), hence on shutdown we don't execve()
 315         systemd-shutdown.
 316
 317 ENGINEERING AND CONSULTING SERVICES:
 318         Kinvolk (https://kinvolk.io) offers professional engineering
 319         and consulting services for systemd. Please contact Chris Kühl
 320         <chris@kinvolk.io> for more information.