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