mirror of
https://github.com/systemd/systemd
synced 2024-11-05 18:25:39 +00:00
449 lines
21 KiB
Text
449 lines
21 KiB
Text
systemd System and Service Manager
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WEB SITE:
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https://systemd.io
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GIT:
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git@github.com:systemd/systemd.git
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https://github.com/systemd/systemd
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MAILING LIST:
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https://lists.freedesktop.org/mailman/listinfo/systemd-devel
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IRC:
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#systemd on irc.libera.chat
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BUG REPORTS:
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https://github.com/systemd/systemd/issues
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OLDER DOCUMENTATION:
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https://0pointer.de/blog/projects/systemd.html
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https://www.freedesktop.org/wiki/Software/systemd
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AUTHOR:
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Lennart Poettering
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Kay Sievers
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...and many others
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LICENSE:
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LGPL-2.1-or-later for all code, exceptions noted in LICENSES/README.md
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REQUIREMENTS:
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Linux kernel ≥ 3.15
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≥ 4.3 for ambient capabilities
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≥ 4.5 for pids controller in cgroup v2
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≥ 4.6 for cgroup namespaces
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≥ 4.9 for RENAME_NOREPLACE support in vfat
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≥ 4.10 for cgroup-bpf egress and ingress hooks
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≥ 4.15 for cgroup-bpf device hook and cpu controller in cgroup v2
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≥ 4.17 for cgroup-bpf socket address hooks
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≥ 4.20 for PSI (used by systemd-oomd)
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≥ 5.3 for bounded loops in BPF program
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≥ 5.4 for signed Verity images
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≥ 5.7 for BPF links and the BPF LSM hook
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⛔ Kernel versions below 3.15 ("minimum baseline") are not supported at
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all, and are missing required functionality (e.g. CLOCK_BOOTTIME
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support for timerfd_create()).
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⚠️ Kernel versions below 4.15 ("recommended baseline") have significant
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gaps in functionality and are not recommended for use with this version
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of systemd (e.g. lack sufficiently comprehensive and working cgroupv2
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support). Taint flag 'old-kernel' will be set. systemd will most likely
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still function, but upstream support and testing are limited.
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Kernel Config Options:
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CONFIG_DEVTMPFS
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CONFIG_CGROUPS (it is OK to disable all controllers)
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CONFIG_INOTIFY_USER
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CONFIG_SIGNALFD
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CONFIG_TIMERFD
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CONFIG_EPOLL
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CONFIG_UNIX (it requires CONFIG_NET, but every other flag in it is not necessary)
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CONFIG_SYSFS
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CONFIG_PROC_FS
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CONFIG_FHANDLE (libudev, mount and bind mount handling)
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udev will fail to work with the legacy sysfs layout:
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CONFIG_SYSFS_DEPRECATED=n
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Legacy hotplug slows down the system and confuses udev:
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CONFIG_UEVENT_HELPER_PATH=""
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Userspace firmware loading is not supported and should be disabled in
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the kernel:
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CONFIG_FW_LOADER_USER_HELPER=n
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Some udev rules and virtualization detection relies on it:
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CONFIG_DMIID
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Support for some SCSI devices serial number retrieval, to create
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additional symlinks in /dev/disk/ and /dev/tape:
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CONFIG_BLK_DEV_BSG
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Required for PrivateNetwork= in service units:
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CONFIG_NET_NS
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Note that systemd-localed.service and other systemd units use
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PrivateNetwork so this is effectively required.
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Required for PrivateUsers= in service units:
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CONFIG_USER_NS
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Optional but strongly recommended:
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CONFIG_IPV6
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CONFIG_AUTOFS_FS
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CONFIG_TMPFS_XATTR
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CONFIG_{TMPFS,EXT4_FS,XFS,BTRFS_FS,...}_POSIX_ACL
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CONFIG_SECCOMP
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CONFIG_SECCOMP_FILTER (required for seccomp support)
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CONFIG_KCMP (for the kcmp() syscall, used to be under
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CONFIG_CHECKPOINT_RESTORE before ~5.12)
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CONFIG_NET_SCHED
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CONFIG_NET_SCH_FQ_CODEL
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Required for CPUShares= in resource control unit settings:
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CONFIG_CGROUP_SCHED
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CONFIG_FAIR_GROUP_SCHED
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Required for CPUQuota= in resource control unit settings:
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CONFIG_CFS_BANDWIDTH
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Required for IPAddressDeny=, IPAddressAllow=, IPIngressFilterPath=,
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IPEgressFilterPath= in resource control unit settings unit settings:
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CONFIG_BPF
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CONFIG_BPF_SYSCALL
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CONFIG_BPF_JIT
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CONFIG_HAVE_EBPF_JIT
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CONFIG_CGROUP_BPF
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Required for SocketBind{Allow|Deny}=, RestrictNetworkInterfaces= in
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resource control unit settings:
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CONFIG_BPF
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CONFIG_BPF_SYSCALL
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CONFIG_BPF_JIT
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CONFIG_HAVE_EBPF_JIT
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CONFIG_CGROUP_BPF
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For UEFI systems:
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CONFIG_EFIVAR_FS
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CONFIG_EFI_PARTITION
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Required for signed Verity images support:
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CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
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Required to verify signed Verity images using keys enrolled in the MoK
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(Machine-Owner Key) keyring:
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CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING
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CONFIG_IMA_ARCH_POLICY
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CONFIG_INTEGRITY_MACHINE_KEYRING
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Required for reading credentials from SMBIOS:
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CONFIG_DMI
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CONFIG_DMI_SYSFS
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Required for RestrictFileSystems= in service units:
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CONFIG_BPF
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CONFIG_BPF_SYSCALL
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CONFIG_BPF_LSM
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CONFIG_DEBUG_INFO_BTF
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CONFIG_LSM="...,bpf" or kernel booted with lsm="...,bpf".
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We recommend to turn off Real-Time group scheduling in the kernel when
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using systemd. RT group scheduling effectively makes RT scheduling
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unavailable for most userspace, since it requires explicit assignment of
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RT budgets to each unit whose processes making use of RT. As there's no
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sensible way to assign these budgets automatically this cannot really be
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fixed, and it's best to disable group scheduling hence:
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CONFIG_RT_GROUP_SCHED=n
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It's a good idea to disable the implicit creation of networking bonding
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devices by the kernel networking bonding module, so that the
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automatically created "bond0" interface doesn't conflict with any such
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device created by systemd-networkd (or other tools). Ideally there would
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be a kernel compile-time option for this, but there currently isn't. The
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next best thing is to make this change through a modprobe.d drop-in.
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This is shipped by default, see modprobe.d/systemd.conf.
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Required for systemd-nspawn:
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CONFIG_DEVPTS_MULTIPLE_INSTANCES or Linux kernel >= 4.7
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Required for systemd-oomd:
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CONFIG_PSI
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Note that kernel auditing is broken when used with systemd's container
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code. When using systemd in conjunction with containers, please make
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sure to either turn off auditing at runtime using the kernel command
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line option "audit=0", or turn it off at kernel compile time using:
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CONFIG_AUDIT=n
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If systemd is compiled with libseccomp support on architectures which do
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not use socketcall() and where seccomp is supported (this effectively
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means x86-64 and ARM, but excludes 32-bit x86!), then nspawn will now
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install a work-around seccomp filter that makes containers boot even
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with audit being enabled. This works correctly only on kernels 3.14 and
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newer though. TL;DR: turn audit off, still.
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glibc >= 2.16
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libcap
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libmount >= 2.30 (from util-linux)
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(util-linux *must* be built without --enable-libmount-support-mtab)
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libseccomp >= 2.3.1 (optional)
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libblkid >= 2.24 (from util-linux) (optional)
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libkmod >= 15 (optional)
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PAM >= 1.1.2 (optional)
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libcryptsetup (optional), >= 2.3.0 required for signed Verity images support
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libaudit (optional)
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libacl (optional)
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libbpf >= 0.1.0 (optional)
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libfdisk >= 2.32 (from util-linux) (optional)
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libselinux (optional)
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liblzma (optional)
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liblz4 >= 1.3.0 / 130 (optional)
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libzstd >= 1.4.0 (optional)
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libgcrypt (optional)
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libqrencode (optional)
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libmicrohttpd (optional)
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libidn2 or libidn (optional)
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gnutls >= 3.1.4 (optional, >= 3.6.0 is required to support DNS-over-TLS with gnutls)
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openssl >= 1.1.0 (optional, required to support DNS-over-TLS with openssl)
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elfutils >= 158 (optional)
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polkit (optional)
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tzdata >= 2014f (optional)
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pkg-config
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gperf
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docbook-xsl (optional, required for documentation)
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xsltproc (optional, required for documentation)
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python >= 3.7 (required by meson too, >= 3.9 is required for ukify)
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python-jinja2
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python-pefile (optional, required for ukify)
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python-lxml (optional, required to build the indices)
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pyelftools (optional, required for systemd-boot)
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meson >= 0.60.0
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ninja
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gcc >= 8.4
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awk, sed, grep, and similar tools
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clang >= 10.0, llvm >= 10.0 (optional, required to build BPF programs
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from source code in C)
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During runtime, you need the following additional
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dependencies:
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util-linux >= v2.27.1 required (including but not limited to: mount,
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umount, swapon, swapoff, sulogin,
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agetty, fsck)
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dbus >= 1.4.0 (strictly speaking optional, but recommended)
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NOTE: If using dbus < 1.9.18, you should override the default
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policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
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polkit (optional)
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To build in directory build/:
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meson setup build/ && ninja -C build/
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Any configuration options can be specified as -Darg=value... arguments
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to meson. After the build directory is initially configured, meson will
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refuse to run again, and options must be changed with:
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meson configure -Darg=value build/
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meson configure without any arguments will print out available options and
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their current values.
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Useful commands:
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ninja -C build -v some/target
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meson test -C build/
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sudo meson install -C build/ --no-rebuild
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DESTDIR=... meson install -C build/
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A tarball can be created with:
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v=250 && git archive --prefix=systemd-$v/ v$v | zstd >systemd-$v.tar.zstd
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When systemd-hostnamed is used, it is strongly recommended to install
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nss-myhostname to ensure that, in a world of dynamically changing
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hostnames, the hostname stays resolvable under all circumstances. In
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fact, systemd-hostnamed will warn if nss-myhostname is not installed.
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nss-systemd must be enabled on systemd systems, as that's required for
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DynamicUser= to work. Note that we ship services out-of-the-box that
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make use of DynamicUser= now, hence enabling nss-systemd is not
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optional.
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Note that the build prefix for systemd must be /usr/. (Moreover, packages
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systemd relies on — such as D-Bus — really should use the same prefix,
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otherwise you are on your own.) Split-usr and unmerged-usr systems are no
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longer supported, and moving everything under /usr/ is required. Systems
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with a separate /usr/ partition must mount it before transitioning into it
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(i.e.: from the initrd). For more information see:
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https://systemd.io/SEPARATE_USR_IS_BROKEN
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https://systemd.io/THE_CASE_FOR_THE_USR_MERGE
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Additional packages are necessary to run some tests:
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- nc (used by test/TEST-12-ISSUE-3171)
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- python (test-udev which is installed is in python)
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- python-pyparsing
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- python-evdev (used by hwdb parsing tests)
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- strace (used by test/test-functions)
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- capsh (optional, used by test-execute)
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POLICY FOR SUPPORT OF DISTRIBUTIONS AND ARCHITECTURES:
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systemd main branch and latest major or stable releases are generally
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expected to compile on current versions of popular distributions (at
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least all non-EOL versions of Fedora, Debian unstable/testing/stable,
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latest Ubuntu LTS and non-LTS releases, openSUSE Tumbleweed/Leap,
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CentOS Stream 8 and 9, up-to-date Arch, etc.) We will generally
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attempt to support also other non-EOL versions of various distros.
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Features which would break compilation on slightly older distributions
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will only be introduced if there are significant reasons for this
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(i.e. supporting them interferes with development or requires too many
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resources to support). In some cases backports of specific libraries or
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tools might be required.
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The policy is similar for architecture support. systemd is regularly
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tested on popular architectures (currently amd64, i386, arm64, ppc64el,
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and s390x), but should compile and work also on other architectures, for
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which support has been added. systemd will emit warnings when
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architecture-specific constants are not defined.
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STATIC COMPILATION AND "STANDALONE" BINARIES:
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systemd provides a public shared libraries libsystemd.so and
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libudev.so. The latter is deprecated, and the sd-device APIs in
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libsystemd should be used instead for new code. In addition, systemd is
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built with a private shared library, libsystemd-shared-<suffix>.so,
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that also includes the libsystemd code, and by default most systemd
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binaries are linked to it. Using shared libraries saves disk space and
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memory at runtime, because only one copy of the code is needed.
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It is possible to build static versions of systemd public shared
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libraries (via the configuration options '-Dstatic-libsystemd' and
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'-Dstatic-libudev'). This allows the libsystemd and libudev code to be
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linked statically into programs. Note that mixing & matching different
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versions of libsystemd and systemd is generally not recommended, since
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various of its APIs wrap internal state and protocols of systemd
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(e.g. logind and udev databases), which are not considered
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stable. Hence, using static libraries is not recommended since it
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generally means that version of the static libsystemd linked into
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applications and the host systemd are not in sync, and will thus create
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compatibility problems.
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In addition, it is possible to disable the use of
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libsystemd-shared-<suffix>.so for various components (via the
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configuration options '-Dlink-*-shared'). In this mode, the libsystemd
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and libsystemd-shared code is linked statically into selected
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binaries. This option is intended for systems where some of the
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components are intended to be delivered independently of the main
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systemd package. Finally, some binaries can be compiled in a second
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version (via the configuration option '-Dstandalone-binaries'). The
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version suffixed with ".standalone" has the libsystemd and
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libsystemd-shared code linked statically. Those binaries are intended
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as replacements to be used in limited installations where the full
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systemd suite is not installed. Yet another option is to rebuild
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systemd with a different '-Dshared-lib-tag' setting, allowing different
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systemd binaries to be linked to instances of the private shared
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library that can be installed in parallel.
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Again: Using the default shared linking is recommended, building static
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or "standalone" versions is not. Mixing versions of systemd components
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that would normally be built and used together (in particular various
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daemons and the manager) is not recommended: we do not test such
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combinations upstream and cannot provide support. Distributors making
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use of those options are responsible if things do not work as expected.
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USERS AND GROUPS:
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Default udev rules use the following standard system group names, which
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need to be resolvable by getgrnam() at any time, even in the very early
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boot stages, where no other databases and network are available:
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audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
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During runtime, the journal daemon requires the "systemd-journal" system
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group to exist. New journal files will be readable by this group (but
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not writable), which may be used to grant specific users read access. In
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addition, system groups "wheel" and "adm" will be given read-only access
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to journal files using systemd-tmpfiles-setup.service.
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The journal remote daemon requires the "systemd-journal-remote" system
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user and group to exist. During execution this network facing service
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will drop privileges and assume this uid/gid for security reasons.
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Similarly, the network management daemon requires the "systemd-network"
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system user and group to exist.
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Similarly, the name resolution daemon requires the "systemd-resolve"
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system user and group to exist.
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Similarly, the coredump support requires the "systemd-coredump" system
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user and group to exist.
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GLIBC NSS:
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systemd ships with four glibc NSS modules:
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nss-myhostname resolves the local hostname to locally configured IP
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addresses, as well as "localhost" to 127.0.0.1/::1.
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nss-resolve enables DNS resolution via the systemd-resolved DNS/LLMNR
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caching stub resolver "systemd-resolved".
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nss-mymachines enables resolution of all local containers registered
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with machined to their respective IP addresses.
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nss-systemd enables resolution of users/group registered via the
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User/Group Record Lookup API (https://systemd.io/USER_GROUP_API),
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including all dynamically allocated service users. (See the
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DynamicUser= setting in unit files.)
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To make use of these NSS modules, please add them to the "hosts:",
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"passwd:", "group:", "shadow:" and "gshadow:" lines in
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/etc/nsswitch.conf.
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The four modules should be used in the following order:
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passwd: files systemd
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group: files [SUCCESS=merge] systemd
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shadow: files systemd
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gshadow: files systemd
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hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
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SYSV INIT.D SCRIPTS:
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When calling "systemctl enable/disable/is-enabled" on a unit which is a
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SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
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this needs to translate the action into the distribution specific
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mechanism such as chkconfig or update-rc.d. Packagers need to provide
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this script if you need this functionality (you don't if you disabled
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SysV init support).
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Please see src/systemctl/systemd-sysv-install.SKELETON for how this
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needs to look like, and provide an implementation at the marked places.
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WARNINGS and TAINT FLAGS:
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systemd requires that the /run mount point exists. systemd also
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requires that /var/run is a symlink to /run. Taint flag 'var-run-bad'
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will be set when this condition is detected.
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Systemd will also warn when the cgroup support is unavailable in the
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kernel (taint flag 'cgroups-missing'), the system is using the old
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cgroup hierarchy (taint flag 'cgroupsv1'), the hardware clock is
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running in non-UTC mode (taint flag 'local-hwclock'), the kernel
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overflow UID or GID are not 65534 (taint flags 'overflowuid-not-65534'
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and 'overflowgid-not-65534'), the UID or GID range assigned to the
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running systemd instance covers less than 0…65534 (taint flags
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'short-uid-range' and 'short-gid-range').
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Taint conditions are logged during boot, but may also be checked at any
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time with:
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busctl get-property org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager Tainted
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See org.freedesktop.systemd1(5) for more information.
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VALGRIND:
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To run systemd under valgrind, compile systemd with the valgrind
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development headers available (i.e. valgrind-devel or equivalent).
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Otherwise, false positives will be triggered by code which violates
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some rules but is actually safe. Note that valgrind generates nice
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output only on exit(), hence on shutdown we don't execve()
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systemd-shutdown.
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STABLE BRANCHES AND BACKPORTS:
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Stable branches with backported patches are available in the
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systemd-stable repo at https://github.com/systemd/systemd-stable.
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Stable branches are started for certain releases of systemd and named
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after them, e.g. v238-stable. Stable branches are managed by
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distribution maintainers on an as needed basis. See
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https://systemd.io/BACKPORTS for some more information and examples.
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