systemd System and Service Manager WEB SITE: https://systemd.io GIT: git@github.com:systemd/systemd.git https://github.com/systemd/systemd MAILING LIST: https://lists.freedesktop.org/mailman/listinfo/systemd-devel IRC: #systemd on irc.libera.chat BUG REPORTS: https://github.com/systemd/systemd/issues OLDER DOCUMENTATION: http://0pointer.de/blog/projects/systemd.html https://www.freedesktop.org/wiki/Software/systemd AUTHOR: Lennart Poettering Kay Sievers ...and many others LICENSE: LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md REQUIREMENTS: Linux kernel ≥ 3.15 ≥ 4.3 for ambient capabilities ≥ 4.5 for pids controller in cgroup v2 ≥ 4.6 for cgroup namespaces ≥ 4.9 for RENAME_NOREPLACE support in vfat ≥ 4.10 for cgroup-bpf egress and ingress hooks ≥ 4.15 for cgroup-bpf device hook and cpu controller in cgroup v2 ≥ 4.17 for cgroup-bpf socket address hooks ≥ 4.20 for PSI (used by systemd-oomd) ≥ 5.3 for bounded loops in BPF program ≥ 5.4 for signed Verity images ≥ 5.7 for BPF links and the BPF LSM hook Kernel versions below 4.15 have significant gaps in functionality and are not recommended for use with this version of systemd. Taint flag 'old-kernel' will be set. Systemd will most likely still function, but upstream support and testing are limited. Kernel Config Options: CONFIG_DEVTMPFS CONFIG_CGROUPS (it is OK to disable all controllers) CONFIG_INOTIFY_USER CONFIG_SIGNALFD CONFIG_TIMERFD CONFIG_EPOLL CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary) CONFIG_SYSFS CONFIG_PROC_FS CONFIG_FHANDLE (libudev, mount and bind mount handling) Kernel crypto/hash API: CONFIG_CRYPTO_USER_API_HASH CONFIG_CRYPTO_HMAC CONFIG_CRYPTO_SHA256 udev will fail to work with the legacy sysfs layout: CONFIG_SYSFS_DEPRECATED=n Legacy hotplug slows down the system and confuses udev: CONFIG_UEVENT_HELPER_PATH="" Userspace firmware loading is not supported and should be disabled in the kernel: CONFIG_FW_LOADER_USER_HELPER=n Some udev rules and virtualization detection relies on it: CONFIG_DMIID Support for some SCSI devices serial number retrieval, to create additional symlinks in /dev/disk/ and /dev/tape: CONFIG_BLK_DEV_BSG Required for PrivateNetwork= in service units: CONFIG_NET_NS Note that systemd-localed.service and other systemd units use PrivateNetwork so this is effectively required. Required for PrivateUsers= in service units: CONFIG_USER_NS Optional but strongly recommended: CONFIG_IPV6 CONFIG_AUTOFS_FS CONFIG_TMPFS_XATTR CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL CONFIG_SECCOMP CONFIG_SECCOMP_FILTER (required for seccomp support) CONFIG_KCMP (for the kcmp() syscall, used to be under CONFIG_CHECKPOINT_RESTORE before ~5.12) Required for CPUShares= in resource control unit settings: CONFIG_CGROUP_SCHED CONFIG_FAIR_GROUP_SCHED Required for CPUQuota= in resource control unit settings: CONFIG_CFS_BANDWIDTH Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=, IPEgressFilterPath= in resource control unit settings unit settings: CONFIG_BPF CONFIG_BPF_SYSCALL CONFIG_BPF_JIT CONFIG_HAVE_EBPF_JIT CONFIG_CGROUP_BPF Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in resource control unit settings: CONFIG_BPF CONFIG_BPF_SYSCALL CONFIG_BPF_JIT CONFIG_HAVE_EBPF_JIT CONFIG_CGROUP_BPF For UEFI systems: CONFIG_EFIVAR_FS CONFIG_EFI_PARTITION Required for signed Verity images support: CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG Required for RestrictFileSystems= in service units: CONFIG_BPF CONFIG_BPF_SYSCALL CONFIG_BPF_LSM CONFIG_DEBUG_INFO_BTF CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf". We recommend to turn off Real-Time group scheduling in the kernel when using systemd. RT group scheduling effectively makes RT scheduling unavailable for most userspace, since it requires explicit assignment of RT budgets to each unit whose processes making use of RT. As there's no sensible way to assign these budgets automatically this cannot really be fixed, and it's best to disable group scheduling hence: CONFIG_RT_GROUP_SCHED=n It's a good idea to disable the implicit creation of networking bonding devices by the kernel networking bonding module, so that the automatically created "bond0" interface doesn't conflict with any such device created by systemd-networkd (or other tools). Ideally there would be a kernel compile-time option for this, but there currently isn't. The next best thing is to make this change through a modprobe.d drop-in. This is shipped by default, see modprobe.d/systemd.conf. Required for systemd-nspawn: CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7 Required for systemd-oomd: CONFIG_PSI Note that kernel auditing is broken when used with systemd's container code. When using systemd in conjunction with containers, please make sure to either turn off auditing at runtime using the kernel command line option "audit=0", or turn it off at kernel compile time using: CONFIG_AUDIT=n If systemd is compiled with libseccomp support on architectures which do not use socketcall() and where seccomp is supported (this effectively means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now install a work-around seccomp filter that makes containers boot even with audit being enabled. This works correctly only on kernels 3.14 and newer though. TL;DR: turn audit off, still. glibc >= 2.16 libcap libmount >= 2.30 (from util-linux) (util-linux *must* be built without --enable-libmount-support-mtab) libseccomp >= 2.3.1 (optional) libblkid >= 2.24 (from util-linux) (optional) libkmod >= 15 (optional) PAM >= 1.1.2 (optional) libcryptsetup (optional), >= 2.3.0 required for signed Verity images support libaudit (optional) libacl (optional) libbpf >= 0.2.0 (optional) libfdisk >= 2.32 (from util-linux) (optional) libselinux (optional) liblzma (optional) liblz4 >= 1.3.0 / 130 (optional) libzstd >= 1.4.0 (optional) libgcrypt (optional) libqrencode (optional) libmicrohttpd (optional) libpython (optional) libidn2 or libidn (optional) gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls) openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl) elfutils >= 158 (optional) polkit (optional) tzdata >= 2014f (optional) pkg-config gperf docbook-xsl (optional, required for documentation) xsltproc (optional, required for documentation) python-jinja2 python-lxml (optional, required to build the indices) python >= 3.5 meson >= 0.53.2 ninja gcc, awk, sed, grep, and similar tools clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs from source code in C) gnu-efi >= 3.0.5 (optional, required for systemd-boot) During runtime, you need the following additional dependencies: util-linux >= v2.27.1 required dbus >= 1.4.0 (strictly speaking optional, but recommended) NOTE: If using dbus < 1.9.18, you should override the default policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d). dracut (optional) polkit (optional) To build in directory build/: meson setup build/ && ninja -C build/ Any configuration options can be specified as -Darg=value... arguments to meson. After the build directory is initially configured, meson will refuse to run again, and options must be changed with: meson configure -Darg=value build/ meson configure without any arguments will print out available options and their current values. Useful commands: ninja -C build -v some/target meson test -C build/ sudo meson install -C build/ --no-rebuild DESTDIR=... meson install -C build/ A tarball can be created with: v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd When systemd-hostnamed is used, it is strongly recommended to install nss-myhostname to ensure that, in a world of dynamically changing hostnames, the hostname stays resolvable under all circumstances. In fact, systemd-hostnamed will warn if nss-myhostname is not installed. nss-systemd must be enabled on systemd systems, as that's required for DynamicUser= to work. Note that we ship services out-of-the-box that make use of DynamicUser= now, hence enabling nss-systemd is not optional. Note that the build prefix for systemd must be /usr. (Moreover, packages systemd relies on — such as D-Bus — really should use the same prefix, otherwise you are on your own.) -Dsplit-usr=false (which is the default and does not need to be specified) is the recommended setting. -Dsplit-usr=true can be used to give a semblance of support for systems with programs installed split between / and /usr. Moving everything under /usr is strongly encouraged. Additional packages are necessary to run some tests: - busybox (used by test/TEST-13-NSPAWN-SMOKE) - nc (used by test/TEST-12-ISSUE-3171) - python3-pyparsing - python3-evdev (used by hwdb parsing tests) - strace (used by test/test-functions) - capsh (optional, used by test-execute) POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES: systemd main branch and latest major or stable releases are generally expected to compile on current versions of popular distributions (at least all non-EOL versions of Fedora, Debian unstable/testing/stable, latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap, CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally attempt to support also other non-EOL versions of various distros. Features which would break compilation on slightly-older distributions will only be introduced if there are significant reasons for this (i.e. supporting them interferes with development or requires too many resources to support). In some cases backports of specific libraries or tools might be required. The policy is similar wrt. architecture support. systemd is regularly tested on popular architectures (currently amd64, i386, arm64, ppc64el, and s390x), but should compile and work also on other architectures, for which support has been added. systemd will emit warnings when architecture-specific constants are not defined. USERS AND GROUPS: Default udev rules use the following standard system group names, which need to be resolvable by getgrnam() at any time, even in the very early boot stages, where no other databases and network are available: audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video During runtime, the journal daemon requires the "systemd-journal" system group to exist. New journal files will be readable by this group (but not writable), which may be used to grant specific users read access. In addition, system groups "wheel" and "adm" will be given read-only access to journal files using systemd-tmpfiles.service. The journal remote daemon requires the "systemd-journal-remote" system user and group to exist. During execution this network facing service will drop privileges and assume this uid/gid for security reasons. Similarly, the network management daemon requires the "systemd-network" system user and group to exist. Similarly, the name resolution daemon requires the "systemd-resolve" system user and group to exist. Similarly, the coredump support requires the "systemd-coredump" system user and group to exist. NSS: systemd ships with four glibc NSS modules: nss-myhostname resolves the local hostname to locally configured IP addresses, as well as "localhost" to 127.0.0.1/::1. nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR caching stub resolver "systemd-resolved". nss-mymachines enables resolution of all local containers registered with machined to their respective IP addresses. nss-systemd enables resolution of users/group registered via the User/Group Record Lookup API (https://systemd.io/USER_GROUP_API), including all dynamically allocated service users. (See the DynamicUser= setting in unit files.) To make use of these NSS modules, please add them to the "hosts:", "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve" module should replace the glibc "dns" module in this file (and don't worry, it chain-loads the "dns" module if it can't talk to resolved). The four modules should be used in the following order: passwd: compat systemd group: compat systemd hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname SYSV INIT.D SCRIPTS: When calling "systemctl enable/disable/is-enabled" on a unit which is a SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install; this needs to translate the action into the distribution specific mechanism such as chkconfig or update-rc.d. Packagers need to provide this script if you need this functionality (you don't if you disabled SysV init support). Please see src/systemctl/systemd-sysv-install.SKELETON for how this needs to look like, and provide an implementation at the marked places. WARNINGS and TAINT FLAGS: systemd will warn during early boot if /usr is not already mounted at this point (that means: either located on the same file system as / or already mounted in the initrd). While in systemd itself very little will break if /usr is on a separate late-mounted partition, many of its dependencies very likely will break sooner or later in one form or another. For example, udev rules tend to refer to binaries in /usr, binaries that link to libraries in /usr or binaries that refer to data files in /usr. Since these breakages are not always directly visible, systemd will warn about this. Such setups are not really supported by the basic set of Linux OS components. Taint flag 'split-usr' will be set when this condition is detected. For more information on this issue consult https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken systemd will warn if the filesystem is not usr-merged (i.e.: /bin, /sbin and /lib* are not symlinks to their counterparts under /usr). Taint flag 'unmerged-usr' will be set when this condition is detected. For more information on this issue consult https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge systemd requires that the /run mount point exists. systemd also requires that /var/run is a symlink to /run. Taint flag 'var-run-bad' will be set when this condition is detected. Systemd will also warn when the cgroup support is unavailable in the kernel (taint flag 'cgroups-missing'), the system is using the old cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is running in non-UTC mode (taint flag 'local-hwclock'), the kernel overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534' and 'overflowgid-not-65534'), the UID or GID range assigned to the running systemd instance covers less than 0…65534 (taint flags 'short-uid-range' and 'short-gid-range'). Taint conditions are logged during boot, but may also be checked at any time with: busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted VALGRIND: To run systemd under valgrind, compile with meson option -Dvalgrind=true and have valgrind development headers installed (i.e. valgrind-devel or equivalent). Otherwise, false positives will be triggered by code which violates some rules but is actually safe. Note that valgrind generates nice output only on exit(), hence on shutdown we don't execve() systemd-shutdown. STABLE BRANCHES AND BACKPORTS: Stable branches with backported patches are available in the systemd-stable repo at https://github.com/systemd/systemd-stable. Stable branches are started for certain releases of systemd and named after them, e.g. v238-stable. Stable branches are managed by distribution maintainers on an as needed basis. See https://www.freedesktop.org/wiki/Software/systemd/Backports/ for some more information and examples.