[systemd-devel] systemd 247 released

systemd tag bot donotreply-systemd-tag at refi64.com
Thu Nov 26 18:03:35 UTC 2020

🎆 A new, official systemd release has just 🎉 been 🎊 tagged 🍾. Please download the tarball here:


Changes since the previous release:

        * KERNEL API INCOMPATIBILITY: Linux 4.14 introduced two new uevents
          "bind" and "unbind" to the Linux device model. When this kernel
          change was made, systemd-udevd was only minimally updated to handle
          and propagate these new event types. The introduction of these new
          uevents (which are typically generated for USB devices and devices
          needing a firmware upload before being functional) resulted in a
          number of issues which we so far didn't address. We hoped the kernel
          maintainers would themselves address these issues in some form, but
          that did not happen. To handle them properly, many (if not most) udev
          rules files shipped in various packages need updating, and so do many
          programs that monitor or enumerate devices with libudev or sd-device,
          or otherwise process uevents. Please note that this incompatibility
          is not fault of systemd or udev, but caused by an incompatible kernel
          change that happened back in Linux 4.12, but is becoming more and
          more visible as the new uevents are generated by more kernel drivers.

          To minimize issues resulting from this kernel change (but not avoid
          them entirely) starting with systemd-udevd 247 the udev "tags"
          concept (which is a concept for marking and filtering devices during
          enumeration and monitoring) has been reworked: udev tags are now
          "sticky", meaning that once a tag is assigned to a device it will not
          be removed from the device again until the device itself is removed
          (i.e. unplugged). This makes sure that any application monitoring
          devices that match a specific tag is guaranteed to both see uevents
          where the device starts being relevant, and those where it stops
          being relevant (the latter now regularly happening due to the new
          "unbind" uevent type). The udev tags concept is hence now a concept
          tied to a *device* instead of a device *event* — unlike for example
          udev properties whose lifecycle (as before) is generally tied to a
          device event, meaning that the previously determined properties are
          forgotten whenever a new uevent is processed.

          With the newly redefined udev tags concept, sometimes it's necessary
          to determine which tags are the ones applied by the most recent
          uevent/database update, in order to discern them from those
          originating from earlier uevents/database updates of the same
          device. To accommodate for this a new automatic property CURRENT_TAGS
          has been added that works similar to the existing TAGS property but
          only lists tags set by the most recent uevent/database
          update. Similarly, the libudev/sd-device API has been updated with
          new functions to enumerate these 'current' tags, in addition to the
          existing APIs that now enumerate the 'sticky' ones.

          To properly handle "bind"/"unbind" on Linux 4.12 and newer it is
          essential that all udev rules files and applications are updated to
          handle the new events. Specifically:

          • All rule files that currently use a header guard similar to
            ACTION!="add|change",GOTO="xyz_end" should be updated to use
            ACTION=="remove",GOTO="xyz_end" instead, so that the
            properties/tags they add are also applied whenever "bind" (or
            "unbind") is seen. (This is most important for all physical device
            types — those for which "bind" and "unbind" are currently
            generated, for all other device types this change is still
            recommended but not as important — but certainly prepares for
            future kernel uevent type additions).

          • Similarly, all code monitoring devices that contains an 'if' branch
            discerning the "add" + "change" uevent actions from all other
            uevents actions (i.e. considering devices only relevant after "add"
            or "change", and irrelevant on all other events) should be reworked
            to instead negatively check for "remove" only (i.e. considering
            devices relevant after all event types, except for "remove", which
            invalidates the device). Note that this also means that devices
            should be considered relevant on "unbind", even though conceptually
            this — in some form — invalidates the device. Since the precise
            effect of "unbind" is not generically defined, devices should be
            considered relevant even after "unbind", however I/O errors
            accessing the device should then be handled gracefully.

          • Any code that uses device tags for deciding whether a device is
            relevant or not most likely needs to be updated to use the new
            udev_device_has_current_tag() API (or sd_device_has_current_tag()
            in case sd-device is used), to check whether the tag is set at the
            moment an uevent is seen (as opposed to the existing
            udev_device_has_tag() API which checks if the tag ever existed on
            the device, following the API concept redefinition explained

          We are very sorry for this breakage and the requirement to update
          packages using these interfaces. We'd again like to underline that
          this is not caused by systemd/udev changes, but result of a kernel
          behaviour change.

        * UPCOMING INCOMPATIBILITY: So far most downstream distribution
          packages have not retriggered devices once the udev package (or any
          auxiliary package installing additional udev rules) is updated. We
          intend to work with major distributions to change this, so that
          "udevadm trigger -a change" is issued on such upgrades, ensuring that
          the updated ruleset is applied to the devices already discovered, so
          that (asynchronously) after the upgrade completed the udev database
          is consistent with the updated rule set. This means udev rules must
          be ready to be retriggered with a "change" action any time, and
          result in correct and complete udev database entries. While the
          majority of udev rule files known to us currently get this right,
          some don't. Specifically, there are udev rules files included in
          various packages that only set udev properties on the "add" action,
          but do not handle the "change" action. If a device matching those
          rules is retriggered with the "change" action (as is intended here)
          it would suddenly lose the relevant properties. This always has been
          problematic, but as soon as all udev devices are triggered on relevant
          package upgrades this will become particularly so. It is strongly
          recommended to fix offending rules so that they can handle a "change"
          action at any time, and acquire all necessary udev properties even
          then. Or in other words: the header guard mentioned above
          (ACTION=="remove",GOTO="xyz_end") is the correct approach to handle
          this, as it makes sure rules are rerun on "change" correctly, and
          accumulate the correct and complete set of udev properties. udev rule
          definitions that cannot handle "change" events being triggered at
          arbitrary times should be considered buggy.

        * The MountAPIVFS= service file setting now defaults to on if
          RootImage= and RootDirectory= are used, which means that with those
          two settings /proc/, /sys/ and /dev/ are automatically properly set
          up for services. Previous behaviour may be restored by explicitly
          setting MountAPIVFS=off.

        * Since PAM 1.2.0 (2015) configuration snippets may be placed in
          /usr/lib/pam.d/ in addition to /etc/pam.d/. If a file exists in the
          latter it takes precedence over the former, similar to how most of
          systemd's own configuration is handled. Given that PAM stack
          definitions are primarily put together by OS vendors/distributions
          (though possibly overridden by users), this systemd release moves its
          own PAM stack configuration for the "systemd-user" PAM service (i.e.
          for the PAM session invoked by the per-user user at .service instance)
          from /etc/pam.d/ to /usr/lib/pam.d/. We recommend moving all
          packages' vendor versions of their PAM stack definitions from
          /etc/pam.d/ to /usr/lib/pam.d/, but if such OS-wide migration is not
          desired the location to which systemd installs its PAM stack
          configuration may be changed via the -Dpamconfdir Meson option.

        * The runtime dependencies on libqrencode, libpcre2, libidn/libidn2,
          libpwquality and libcryptsetup have been changed to be based on
          dlopen(): instead of regular dynamic library dependencies declared in
          the binary ELF headers, these libraries are now loaded on demand
          only, if they are available. If the libraries cannot be found the
          relevant operations will fail gracefully, or a suitable fallback
          logic is chosen. This is supposed to be useful for general purpose
          distributions, as it allows minimizing the list of dependencies the
          systemd packages pull in, permitting building of more minimal OS
          images, while still making use of these "weak" dependencies should
          they be installed. Since many package managers automatically
          synthesize package dependencies from ELF shared library dependencies,
          some additional manual packaging work has to be done now to replace
          those (slightly downgraded from "required" to "recommended" or
          whatever is conceptually suitable for the package manager). Note that
          this change does not alter build-time behaviour: as before the
          build-time dependencies have to be installed during build, even if
          they now are optional during runtime.

        * sd-event.h gained a new call sd_event_add_time_relative() for
          installing timers relative to the current time. This is mostly a
          convenience wrapper around the pre-existing sd_event_add_time() call
          which installs absolute timers.

        * sd-event event sources may now be placed in a new "exit-on-failure"
          mode, which may be controlled via the new
          sd_event_source_get_exit_on_failure() and
          sd_event_source_set_exit_on_failure() functions. If enabled, any
          failure returned by the event source handler functions will result in
          exiting the event loop (unlike the default behaviour of just
          disabling the event source but continuing with the event loop). This
          feature is useful to set for all event sources that define "primary"
          program behaviour (where failure should be fatal) in contrast to
          "auxiliary" behaviour (where failure should remain local).

        * Most event source types sd-event supports now accept a NULL handler
          function, in which case the event loop is exited once the event
          source is to be dispatched, using the userdata pointer — converted to
          a signed integer — as exit code of the event loop. Previously this
          was supported for IO and signal event sources already. Exit event
          sources still do not support this (simply because it makes little
          sense there, as the event loop is already exiting when they are

        * A new per-unit setting RootImageOptions= has been added which allows
          tweaking the mount options for any file system mounted as effect of
          the RootImage= setting.

        * Another new per-unit setting MountImages= has been added, that allows
          mounting additional disk images into the file system tree accessible
          to the service.

        * Timer units gained a new FixedRandomDelay= boolean setting. If
          enabled, the random delay configured with RandomizedDelaySec= is
          selected in a way that is stable on a given system (though still
          different for different units).

        * Socket units gained a new setting Timestamping= that takes "us", "ns"
          or "off". This controls the SO_TIMESTAMP/SO_TIMESTAMPNS socket

        * systemd-repart now generates JSON output when requested with the new
          --json= switch.

        * systemd-machined's OpenMachineShell() bus call will now pass
          additional policy metadata data fields to the PolicyKit
          authentication request.

        * systemd-tmpfiles gained a new -E switch, which is equivalent to
          --exclude-prefix=/dev --exclude-prefix=/proc --exclude=/run
          --exclude=/sys. It's particularly useful in combination with --root=,
          when operating on OS trees that do not have any of these four runtime
          directories mounted, as this means no files below these subtrees are
          created or modified, since those mount points should probably remain

        * systemd-tmpfiles gained a new --image= switch which is like --root=,
          but takes a disk image instead of a directory as argument. The
          specified disk image is mounted inside a temporary mount namespace
          and the tmpfiles.d/ drop-ins stored in the image are executed and
          applied to the image. systemd-sysusers similarly gained a new
          --image= switch, that allows the sysusers.d/ drop-ins stored in the
          image to be applied onto the image.

        * Similarly, the journalctl command also gained an --image= switch,
          which is a quick one-step solution to look at the log data included
          in OS disk images.

        * journalctl's --output=cat option (which outputs the log content
          without any metadata, just the pure text messages) will now make use
          of terminal colors when run on a suitable terminal, similarly to the
          other output modes.

        * JSON group records now support a "description" string that may be
          used to add a human-readable textual description to such groups. This
          is supposed to match the user's GECOS field which traditionally
          didn't have a counterpart for group records.

        * The "systemd-dissect" tool that may be used to inspect OS disk images
          and that was previously installed to /usr/lib/systemd/ has now been
          moved to /usr/bin/, reflecting its updated status of an officially
          supported tool with a stable interface. It gained support for a new
          --mkdir switch which when combined with --mount has the effect of
          creating the directory to mount the image to if it is missing
          first. It also gained two new commands --copy-from and --copy-to for
          copying files and directories in and out of an OS image without the
          need to manually mount it. It also acquired support for a new option
          --json= to generate JSON output when inspecting an OS image.

        * The cgroup2 file system is now mounted with the
          "memory_recursiveprot" mount option, supported since kernel 5.7. This
          means that the MemoryLow= and MemoryMin= unit file settings now apply
          recursively to whole subtrees.

        * systemd-homed now defaults to using the btrfs file system — if
          available — when creating home directories in LUKS volumes. This may
          be changed with the DefaultFileSystemType= setting in homed.conf.
          It's now the default file system in various major distributions and
          has the major benefit for homed that it can be grown and shrunk while
          mounted, unlike the other contenders ext4 and xfs, which can both be
          grown online, but not shrunk (in fact xfs is the technically most
          limited option here, as it cannot be shrunk at all).

        * JSON user records managed by systemd-homed gained support for
          "recovery keys". These are basically secondary passphrases that can
          unlock user accounts/home directories. They are computer-generated
          rather than user-chosen, and typically have greater entropy.
          homectl's --recovery-key= option may be used to add a recovery key to
          a user account. The generated recovery key is displayed as a QR code,
          so that it can be scanned to be kept in a safe place. This feature is
          particularly useful in combination with systemd-homed's support for
          FIDO2 or PKCS#11 authentication, as a secure fallback in case the
          security tokens are lost. Recovery keys may be entered wherever the
          system asks for a password.

        * systemd-homed now maintains a "dirty" flag for each LUKS encrypted
          home directory which indicates that a home directory has not been
          deactivated cleanly when offline. This flag is useful to identify
          home directories for which the offline discard logic did not run when
          offlining, and where it would be a good idea to log in again to catch

        * systemctl gained a new parameter --timestamp= which may be used to
          change the style in which timestamps are output, i.e. whether to show
          them in local timezone or UTC, or whether to show µs granularity.

        * Alibaba's "pouch" container manager is now detected by
          systemd-detect-virt, ConditionVirtualization= and similar
          constructs. Similar, they now also recognize IBM PowerVM machine

        * systemd-nspawn has been reworked to use the /run/host/incoming/ as
          place to use for propagating external mounts into the
          container. Similarly /run/host/notify is now used as the socket path
          for container payloads to communicate with the container manager
          using sd_notify(). The container manager now uses the
          /run/host/inaccessible/ directory to place "inaccessible" file nodes
          of all relevant types which may be used by the container payload as
          bind mount source to over-mount inodes to make them inaccessible.
          /run/host/container-manager will now be initialized with the same
          string as the $container environment variable passed to the
          container's PID 1. /run/host/container-uuid will be initialized with
          the same string as $container_uuid. This means the /run/host/
          hierarchy is now the primary way to make host resources available to
          the container. The Container Interface documents these new files and


        * Support for the "ConditionNull=" unit file condition has been
          deprecated and undocumented for 6 years. systemd started to warn
          about its use 1.5 years ago. It has now been removed entirely.

        * sd-bus.h gained a new API call sd_bus_error_has_names(), which takes
          a sd_bus_error struct and a list of error names, and checks if the
          error matches one of these names. It's a convenience wrapper that is
          useful in cases where multiple errors shall be handled the same way.

        * A new system call filter list "@known" has been added, that contains
          all system calls known at the time systemd was built.

        * Behaviour of system call filter allow lists has changed slightly:
          system calls that are contained in @known will result in a EPERM by
          default, while those not contained in it result in ENOSYS. This
          should improve compatibility because known system calls will thus be
          communicated as prohibited, while unknown (and thus newer ones) will
          be communicated as not implemented, which hopefully has the greatest
          chance of triggering the right fallback code paths in client

        * "systemd-analyze syscall-filter" will now show two separate sections
          at the bottom of the output: system calls known during systemd build
          time but not included in any of the filter groups shown above, and
          system calls defined on the local kernel but known during systemd
          build time.

        * If the $SYSTEMD_LOG_SECCOMP=1 environment variable is set for
          systemd-nspawn all system call filter violations will be logged by
          the kernel (audit). This is useful for tracking down system calls
          invoked by container payloads that are prohibited by the container's
          system call filter policy.

        * If the $SYSTEMD_SECCOMP=0 environment variable is set for
          systemd-nspawn (and other programs that use seccomp) all seccomp
          filtering is turned off.

        * Two new unit file settings ProtectProc= and ProcSubset= have been
          added that expose the hidepid= and subset= mount options of procfs.
          All processes of the unit will only see processes in /proc that are
          are owned by the unit's user. This is an important new sandboxing
          option that is recommended to be set on all system services. All
          long-running system services that are included in systemd itself set
          this option now. This option is only supported on kernel 5.8 and
          above, since the hidepid= option supported on older kernels was not a
          per-mount option but actually applied to the whole PID namespace.

        * Socket units gained a new boolean setting FlushPending=. If enabled
          all pending socket data/connections are flushed whenever the socket
          unit enters the "listening" state, i.e. after the associated service

        * The unit file setting NUMAMask= gained a new "all" value: when used,
          all existing NUMA nodes are added to the NUMA mask.

        * A new "credentials" logic has been added to system services. This is
          a simple mechanism to pass privileged data to services in a safe and
          secure way. It's supposed to be used to pass per-service secret data
          such as passwords or cryptographic keys but also associated less
          private information such as user names, certificates, and similar to
          system services. Each credential is identified by a short user-chosen
          name and may contain arbitrary binary data. Two new unit file
          settings have been added: SetCredential= and LoadCredential=. The
          former allows setting a credential to a literal string, the latter
          sets a credential to the contents of a file (or data read from a
          user-chosen AF_UNIX stream socket). Credentials are passed to the
          service via a special credentials directory, one file for each
          credential. The path to the credentials directory is passed in a new
          $CREDENTIALS_DIRECTORY environment variable. Since the credentials
          are passed in the file system they may be easily referenced in
          ExecStart= command lines too, thus no explicit support for the
          credentials logic in daemons is required (though ideally daemons
          would look for the bits they need in $CREDENTIALS_DIRECTORY
          themselves automatically, if set). The $CREDENTIALS_DIRECTORY is
          backed by unswappable memory if privileges allow it, immutable if
          privileges allow it, is accessible only to the service's UID, and is
          automatically destroyed when the service stops.

        * systemd-nspawn supports the same credentials logic. It can both
          consume credentials passed to it via the aforementioned
          $CREDENTIALS_DIRECTORY protocol as well as pass these credentials on
          to its payload. The service manager/PID 1 has been updated to match
          this: it can also accept credentials from the container manager that
          invokes it (in fact: any process that invokes it), and passes them on
          to its services. Thus, credentials can be propagated recursively down
          the tree: from a system's service manager to a systemd-nspawn
          service, to the service manager that runs as container payload and to
          the service it runs below. Credentials may also be added on the
          systemd-nspawn command line, using new --set-credential= and
          --load-credential= command line switches that match the
          aforementioned service settings.

        * systemd-repart gained new settings Format=, Encrypt=, CopyFiles= in
          the partition drop-ins which may be used to format/LUKS
          encrypt/populate any created partitions. The partitions are
          encrypted/formatted/populated before they are registered in the
          partition table, so that they appear atomically: either the
          partitions do not exist yet or they exist fully encrypted, formatted,
          and populated — there is no time window where they are
          "half-initialized". Thus the system is robust to abrupt shutdown: if
          the tool is terminated half-way during its operations on next boot it
          will start from the beginning.

        * systemd-repart's --size= operation gained a new "auto" value. If
          specified, and operating on a loopback file it is automatically sized
          to the minimal size the size constraints permit. This is useful to
          use "systemd-repart" as an image builder for minimally sized images.

        * systemd-resolved now gained a third IPC interface for requesting name
          resolution: besides D-Bus and local DNS to a Varlink
          interface is now supported. The nss-resolve NSS module has been
          modified to use this new interface instead of D-Bus. Using Varlink
          has a major benefit over D-Bus: it works without a broker service,
          and thus already during earliest boot, before the dbus daemon has
          been started. This means name resolution via systemd-resolved now
          works at the same time systemd-networkd operates: from earliest boot
          on, including in the initrd.

        * systemd-resolved gained support for a new DNSStubListenerExtra=
          configuration file setting which may be used to specify additional IP
          addresses the built-in DNS stub shall listen on, in addition to the
          main one on

        * Name lookups issued via systemd-resolved's D-Bus and Varlink
          interfaces (and thus also via glibc NSS if nss-resolve is used) will
          now honour a trailing dot in the hostname: if specified the search
          path logic is turned off. Thus "resolvectl query foo." is now
          equivalent to "resolvectl query --search=off foo.".

        * systemd-resolved gained a new D-Bus property "ResolvConfMode" that
          exposes how /etc/resolv.conf is currently managed: by resolved (and
          in which mode if so) or another subsystem. "resolvctl" will display
          this property in its status output.

        * The resolv.conf snippets systemd-resolved provides will now set "."
          as the search domain if no other search domain is known. This turns
          off the derivation of an implicit search domain by nss-dns for the
          hostname, when the hostname is set to an FQDN. This change is done to
          make nss-dns using resolv.conf provided by systemd-resolved behave
          more similarly to nss-resolve.

        * systemd-tmpfiles' file "aging" logic (i.e. the automatic clean-up of
          /tmp/ and /var/tmp/ based on file timestamps) now looks at the
          "birth" time (btime) of a file in addition to the atime, mtime, and

        * systemd-analyze gained a new verb "capability" that lists all known
          capabilities by the systemd build and by the kernel.

        * If a file /usr/lib/clock-epoch exists, PID 1 will read its mtime and
          advance the system clock to it at boot if it is noticed to be before
          that time. Previously, PID 1 would only advance the time to an epoch
          time that is set during build-time. With this new file OS builders
          can change this epoch timestamp on individual OS images without
          having to rebuild systemd.

        * systemd-logind will now listen to the KEY_RESTART key from the Linux
          input layer and reboot the system if it is pressed, similarly to how
          it already handles KEY_POWER, KEY_SUSPEND or KEY_SLEEP. KEY_RESTART
          was originally defined in the Multimedia context (to restart playback
          of a song or film), but is now primarily used in various embedded
          devices for "Reboot" buttons. Accordingly, systemd-logind will now
          honour it as such. This may configured in more detail via the new
          HandleRebootKey= and RebootKeyIgnoreInhibited=.

        * systemd-nspawn/systemd-machined will now reconstruct hardlinks when
          copying OS trees, for example in "systemd-nspawn --ephemeral",
          "systemd-nspawn --template=", "machinectl clone" and similar. This is
          useful when operating with OSTree images, which use hardlinks heavily
          throughout, and where such copies previously resulting in "exploding"

        * systemd-nspawn's --console= setting gained support for a new
          "autopipe" value, which is identical to "interactive" when invoked on
          a TTY, and "pipe" otherwise.

        * systemd-networkd's .network files gained support for explicitly
          configuring the multicast membership entries of bridge devices in the
          [BridgeMDB] section. It also gained support for the PIE queuing
          discipline in the [FlowQueuePIE] sections.

        * systemd-networkd's .netdev files may now be used to create "BareUDP"
          tunnels, configured in the new [BareUDP] setting.

        * systemd-networkd's Gateway= setting in .network files now accepts the
          special values "_dhcp4" and "_ipv6ra" to configure additional,
          locally defined, explicit routes to the gateway acquired via DHCP or
          IPv6 Router Advertisements. The old setting "_dhcp" is deprecated,
          but still accepted for backwards compatibility.

        * systemd-networkd's [IPv6PrefixDelegation] section and
          IPv6PrefixDelegation= options have been renamed as [IPv6SendRA] and
          IPv6SendRA= (the old names are still accepted for backwards

        * systemd-networkd's .network files gained the DHCPv6PrefixDelegation=
          boolean setting in [Network] section. If enabled, the delegated prefix
          gained by another link will be configured, and an address within the
          prefix will be assigned.

        * systemd-networkd's .network files gained the Announce= boolean setting
          in [DHCPv6PrefixDelegation] section. When enabled, the delegated
          prefix will be announced through IPv6 router advertisement (IPv6 RA).
          The setting is enabled by default.

        * VXLAN tunnels may now be marked as independent of any underlying
          network interface via the new Independent= boolean setting.

        * systemctl gained support for two new verbs: "service-log-level" and
          "service-log-target" may be used on services that implement the
          generic org.freedesktop.LogControl1 D-Bus interface to dynamically
          adjust the log level and target. All of systemd's long-running
          services support this now, but ideally all system services would
          implement this interface to make the system more uniformly

        * The SystemCallErrorNumber= unit file setting now accepts the new
          "kill" and "log" actions, in addition to arbitrary error number
          specifications as before. If "kill" the processes are killed on the
          event, if "log" the offending system call is audit logged.

        * A new SystemCallLog= unit file setting has been added that accepts a
          list of system calls that shall be logged about (audit).

        * The OS image dissection logic (as used by RootImage= in unit files or
          systemd-nspawn's --image= switch) has gained support for identifying
          and mounting explicit /usr/ partitions, which are now defined in the
          discoverable partition specification. This should be useful for
          environments where the root file system is
          generated/formatted/populated dynamically on first boot and combined
          with an immutable /usr/ tree that is supplied by the vendor.

        * In the final phase of shutdown, within the systemd-shutdown binary
          we'll now try to detach MD devices (i.e software RAID) in addition to
          loopback block devices and DM devices as before. This is supposed to
          be a safety net only, in order to increase robustness if things go
          wrong. Storage subsystems are expected to properly detach their
          storage volumes during regular shutdown already (or in case of
          storage backing the root file system: in the initrd hook we return to

        * If the SYSTEMD_LOG_TID environment variable is set all systemd tools
          will now log the thread ID in their log output. This is useful when
          working with heavily threaded programs.

        * If the SYSTEMD_RDRAND environment variable is set to "0", systemd will
          not use the RDRAND CPU instruction. This is useful in environments
          such as replay debuggers where non-deterministic behaviour is not

        * The autopaging logic in systemd's various tools (such as systemctl)
          has been updated to turn on "secure" mode in "less"
          (i.e. $LESSECURE=1) if execution in a "sudo" environment is
          detected. This disables invoking external programs from the pager,
          via the pipe logic. This behaviour may be overridden via the new
          $SYSTEMD_PAGERSECURE environment variable.

        * Units which have resource limits (.service, .mount, .swap, .slice,
          .socket, and .slice) gained new configuration settings
          ManagedOOMSwap=, ManagedOOMMemoryPressure=, and
          ManagedOOMMemoryPressureLimitPercent= that specify resource pressure
          limits and optional action taken by systemd-oomd.

        * A new service systemd-oomd has been added. It monitors resource
          contention for selected parts of the unit hierarchy using the PSI
          information reported by the kernel, and kills processes when memory
          or swap pressure is above configured limits. This service is only
          enabled by default in developer mode (see below) and should be
          considered a preview in this release. Behaviour details and option
          names are subject to change without the usual backwards-compatibility

        * A new helper oomctl has been added to introspect systemd-oomd state.
          It is only enabled by default in developer mode and should be
          considered a preview without the usual backwards-compatibility

        * New meson option -Dcompat-mutable-uid-boundaries= has been added. If
          enabled, systemd reads the system UID boundaries from /etc/login.defs
          at runtime, instead of using the built-in values selected during
          build. This is an option to improve compatibility for upgrades from
          old systems. It's strongly recommended not to make use of this
          functionality on new systems (or even enable it during build), as it
          makes something runtime-configurable that is mostly an implementation
          detail of the OS, and permits avoidable differences in deployments
          that create all kinds of problems in the long run.

        * New meson option '-Dmode=developer|release' has been added. When
          'developer', additional checks and features are enabled that are
          relevant during upstream development, e.g. verification that
          semi-automatically-generated documentation has been properly updated
          following API changes. Those checks are considered hints for
          developers and are not actionable in downstream builds. In addition,
          extra features that are not ready for general consumption may be
          enabled in developer mode. It is thus recommended to set
          '-Dmode=release' in end-user and distro builds.

        * systemd-cryptsetup gained support for processing detached LUKS
          headers specified on the kernel command line via the header=
          parameter of the luks.options= kernel command line option. The same
          device/path syntax as for key files is supported for header files
          like this.

        * The "net_id" built-in of udev has been updated to ignore ACPI _SUN
          slot index data for devices that are connected through a PCI bridge
          where the _SUN index is associated with the bridge instead of the
          network device itself. Previously this would create ambiguous device
          naming if multiple network interfaces were connected to the same PCI
          bridge. Since this is a naming scheme incompatibility on systems that
          possess hardware like this it has been introduced as new naming
          scheme "v247". The previous scheme can be selected via the
          "net.naming-scheme=v245" kernel command line parameter.

        * ConditionFirstBoot= semantics have been modified to be safe towards
          abnormal system power-off during first boot. Specifically, the
          "systemd-machine-id-commit.service" service now acts as boot
          milestone indicating when the first boot process is sufficiently
          complete in order to not consider the next following boot also a
          first boot. If the system is reset before this unit is reached the
          first time, the next boot will still be considered a first boot; once
          it has been reached, no further boots will be considered a first
          boot. The "first-boot-complete.target" unit now acts as official hook
          point to order against this. If a service shall be run on every boot
          until the first boot fully succeeds it may thus be ordered before
          this target unit (and pull it in) and carry ConditionFirstBoot=

        * bootctl's set-default and set-oneshot commands now accept the three
          special strings "@default", "@oneshot", "@current" in place of a boot
          entry id. These strings are resolved to the current default and
          oneshot boot loader entry, as well as the currently booted one. Thus
          a command "bootctl set-default @current" may be used to make the
          currently boot menu item the new default for all subsequent boots.

        * "systemctl edit" has been updated to show the original effective unit
          contents in commented form in the text editor.

        * Units in user mode are now segregated into three new slices:
          session.slice (units that form the core of graphical session),
          app.slice ("normal" user applications), and background.slice
          (low-priority tasks). Unless otherwise configured, user units are
          placed in app.slice. The plan is to add resource limits and
          protections for the different slices in the future.

        * New GPT partition types for RISCV32/64 for the root and /usr
          partitions, and their associated Verity partitions have been defined,
          and are now understood by systemd-gpt-auto-generator, and the OS
          image dissection logic.

        Contributions from: Adolfo Jayme Barrientos, afg, Alec Moskvin, Alyssa
        Ross, Amitanand Chikorde, Andrew Hangsleben, Anita Zhang, Ansgar
        Burchardt, Arian van Putten, Aurelien Jarno, Axel Rasmussen, bauen1,
        Beniamino Galvani, Benjamin Berg, Bjørn Mork, brainrom, Chandradeep
        Dey, Charles Lee, Chris Down, Christian Göttsche, Christof Efkemann,
        Christoph Ruegge, Clemens Gruber, Daan De Meyer, Daniele Medri, Daniel
        Mack, Daniel Rusek, Dan Streetman, David Tardon, Dimitri John Ledkov,
        Dmitry Borodaenko, Elias Probst, Elisei Roca, ErrantSpore, Etienne
        Doms, Fabrice Fontaine, fangxiuning, Felix Riemann, Florian Klink,
        Franck Bui, Frantisek Sumsal, fwSmit, George Rawlinson, germanztz,
        Gibeom Gwon, Glen Whitney, Gogo Gogsi, Göran Uddeborg, Grant Mathews,
        Hans de Goede, Hans Ulrich Niedermann, Haochen Tong, Harald Seiler,
        huangyong, Hubert Kario, igo95862, Ikey Doherty, Insun Pyo, Jan Chren,
        Jan Schlüter, Jérémy Nouhaud, Jian-Hong Pan, Joerg Behrmann, Jonathan
        Lebon, Jörg Thalheim, Josh Brobst, Juergen Hoetzel, Julien Humbert,
        Kai-Chuan Hsieh, Kairui Song, Kamil Dudka, Kir Kolyshkin, Kristijan
        Gjoshev, Kyle Huey, Kyle Russell, Lee Whalen, Lennart Poettering,
        lichangze, Luca Boccassi, Lucas Werkmeister, Luca Weiss, Marc
        Kleine-Budde, Marco Wang, Martin Wilck, Marti Raudsepp, masmullin2000,
        Máté Pozsgay, Matt Fenwick, Michael Biebl, Michael Scherer, Michal
        Koutný, Michal Sekletár, Michal Suchanek, Mikael Szreder, Milo
        Casagrande, mirabilos, Mitsuha_QuQ, mog422, Muhammet Kara, Nazar
        Vinnichuk, Nicholas Narsing, Nicolas Fella, Njibhu, nl6720, Oğuz Ersen,
        Olivier Le Moal, Ondrej Kozina, onlybugreports, Pass Automated Testing
        Suite, Pat Coulthard, Pavel Sapezhko, Pedro Ruiz, perry_yuan, Peter
        Hutterer, Phaedrus Leeds, PhoenixDiscord, Piotr Drąg, Plan C,
        Purushottam choudhary, Rasmus Villemoes, Renaud Métrich, Robert Marko,
        Roman Beranek, Ronan Pigott, Roy Chen (陳彥廷), RussianNeuroMancer,
        Samanta Navarro, Samuel BF, scootergrisen, Sorin Ionescu, Steve Dodd,
        Susant Sahani, Timo Rothenpieler, Tobias Hunger, Tobias Kaufmann, Topi
        Miettinen, vanou, Vito Caputo, Weblate, Wen Yang, Whired Planck,
        williamvds, Yu, Li-Yu, Yuri Chornoivan, Yu Watanabe, Zbigniew
        Jędrzejewski-Szmek, Zmicer Turok, Дамјан Георгиевски

        – Warsaw, 2020-11-26

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