systemd-231

[bdubbs@…]

New version

CHANGES WITH 231:

        * In service units the various ExecXYZ= settings have been extended
          with an additional special character as first argument of the
          assigned value: if the character '+' is used the specified command
          line it will be run with full privileges, regardless of User=,
          Group=, CapabilityBoundingSet= and similar options. The effect is
          similar to the existing PermissionsStartOnly= option, but allows
          configuration of this concept for each executed command line
          independently.

        * Services may now alter the service watchdog timeout at runtime by
          sending a WATCHDOG_USEC= message via sd_notify().

        * MemoryLimit= and related unit settings now optionally take percentage
          specifications. The percentage is taken relative to the amount of
          physical memory in the system (or in case of containers, the assigned
          amount of memory). This allows scaling service resources neatly with
          the amount of RAM available on the system. Similarly, systemd-logind's
          RuntimeDirectorySize= option now also optionally takes percentage
          values.

        * In similar fashion TasksMax= takes percentage values now, too. The
          value is taken relative to the configured maximum number of processes
          on the system. The per-service task maximum has been changed to 15%
          using this functionality. (Effectively this is an increase of 512 →
          4915 for service units, given the kernel's default pid_max setting.)

        * Calendar time specifications in .timer units now understand a ".."
          syntax for time ranges. Example: "4..7:10" may now be used for
          defining a timer that is triggered at 4:10am, 5:10am, 6:10am and
          7:10am every day.

        * The InaccessableDirectories=, ReadOnlyDirectories= and
          ReadWriteDirectories= unit file settings have been renamed to
          InaccessablePaths=, ReadOnlyPaths= and ReadWritePaths= and may now be
          applied to all kinds of file nodes, and not just directories, with
          the exception of symlinks. Specifically these settings may now be
          used on block and character device nodes, UNIX sockets and FIFOS as
          well as regular files. The old names of these settings remain
          available for compatibility.

        * systemd will now log about all service processes it kills forcibly
          (using SIGKILL) because they remained after the clean shutdown phase
          of the service completed. This should help identifying services that
          shut down uncleanly. Moreover if KillUserProcesses= is enabled in
          systemd-logind's configuration a similar log message is generated for
          processes killed at the end of each session due to this setting.

        * systemd will now set the $JOURNAL_STREAM environment variable for all
          services whose stdout/stderr are connected to the Journal (which
          effectively means by default: all services). The variable contains
          the device and inode number of the file descriptor used for
          stdout/stderr. This may be used by invoked programs to detect whether
          their stdout/stderr is connected to the Journal, in which case they
          can switch over to direct Journal communication, thus being able to
          pass extended, structured metadata along with their log messages. As
          one example, this is now used by glib's logging primitives.

        * When using systemd's default tmp.mount unit for /tmp, the mount point
          will now be established with the "nosuid" and "nodev" options. This
          avoids privilege escalation attacks that put traps and exploits into
          /tmp.  However, this might cause problems if you e. g. put container
          images or overlays into /tmp; if you need this, override tmp.mount's
          "Options=" with a drop-in, or mount /tmp from /etc/fstab with your
          desired options.

        * systemd now supports the "memory" cgroup controller also on
          cgroupsv2.

        * The systemd-cgtop tool now optionally takes a control group path as
          command line argument. If specified, the control group list shown is
          limited to subgroups of that group.

        * The SystemCallFilter= unit file setting gained support for
          pre-defined, named system call filter sets. For example
          SystemCallFilter=@clock is now an effective way to make all clock
          changing-related system calls unavailable to a service. A number of
          similar pre-defined groups are defined. Writing system call filters
          for system services is simplified substantially with this new
          concept. Accordingly, all of systemd's own, long-running services now
          enable system call filtering based on this, by default.

        * A new service setting MemoryDenyWriteExecute= has been added, taking
          a boolean value. If turned on, a service may no longer create memory
          mappings that are writable and executable at the same time. This
          enhances security for services where this is enabled as it becomes
          harder to dynamically write and then execute memory in exploited
          service processes. This option has been enabled for all of systemd's
          own long-running services.

        * A new RestrictRealtime= service setting has been added, taking a
          boolean argument. If set the service's processes may no longer
          acquire realtime scheduling. This improves security as realtime
          scheduling may otherwise be used to easily freeze the system.

        * systemd-nspawn gained a new switch --notify-ready= taking a boolean
          value. This may be used for requesting that the system manager inside
          of the container reports start-up completion to nspawn which then
          propagates this notification further to the service manager
          supervising nspawn itself. A related option NotifyReady= in .nspawn
          files has been added too. This functionality allows ordering of the
          start-up of multiple containers using the usual systemd ordering
          primitives.

        * machinectl gained a new command "stop" that is an alias for
          "terminate".

        * systemd-resolved gained support for contacting DNS servers on
          link-local IPv6 addresses.

        * If systemd-resolved receives the SIGUSR2 signal it will now flush all
          its caches. A method call for requesting the same operation has been
          added to the bus API too, and is made available via "systemd-resolve
          --flush-caches".

        * systemd-resolve gained a new --status switch. If passed a brief
          summary of the used DNS configuration with per-interface information
          is shown.

        * resolved.conf gained a new Cache= boolean option, defaulting to
          on. If turned off local DNS caching is disabled. This comes with a
          performance penalty in particular when DNSSEC is enabled. Note that
          resolved disables its internal caching implicitly anyway, when the
          configured DNS server is on a host-local IP address such as ::1 or
          127.0.0.1, thus automatically avoiding double local caching.

        * systemd-resolved now listens on the local IP address 127.0.0.53:53
          for DNS requests. This improves compatibility with local programs
          that do not use the libc NSS or systemd-resolved's bus APIs for name
          resolution. This minimal DNS service is only available to local
          programs and does not implement the full DNS protocol, but enough to
          cover local DNS clients. A new, static resolv.conf file, listing just
          this DNS server is now shipped in /usr/lib/systemd/resolv.conf. It is
          now recommended to make /etc/resolv.conf a symlink to this file in
          order to route all DNS lookups to systemd-resolved, regardless if
          done via NSS, the bus API or raw DNS packets. Note that this local
          DNS service is not as fully featured as the libc NSS or
          systemd-resolved's bus APIs. For example, as unicast DNS cannot be
          used to deliver link-local address information (as this implies
          sending a local interface index along), LLMNR/mDNS support via this
          interface is severely restricted. It is thus strongly recommended for
          all applications to use the libc NSS API or native systemd-resolved
          bus API instead.

        * systemd-networkd's bridge support learned a new setting
          VLANFiltering= for controlling VLAN filtering. Moreover a new section
          in .network files has been added for configuring VLAN bridging in
          more detail: VLAN=, EgressUntagged=, PVID= in [BridgeVLAN].

        * systemd-networkd's IPv6 Router Advertisement code now makes use of
          the DNSSL and RDNSS options. This means IPv6 DNS configuration may
          now be acquired without relying on DHCPv6. Two new options
          UseDomains= and UseDNS= have been added to configure this behaviour.

        * systemd-networkd's IPv6AcceptRouterAdvertisements= option has been
          renamed IPv6AcceptRA=, without altering its behaviour. The old
          setting name remains available for compatibility reasons.

        * The systemd-networkd VTI/VTI6 tunneling support gained new options
          Key=, InputKey= and OutputKey=.

        * systemd-networkd gained support for VRF ("Virtual Routing Function")
          interface configuration.

        * "systemctl edit" may now be used to create new unit files by
          specifying the --force switch.

        * sd-event gained a new function sd_event_get_iteration() for
          requesting the current iteration counter of the event loop. It starts
          at zero and is increased by one with each event loop iteration.

        * A new rpm macro %systemd_ordering is provided by the macros.systemd
          file. It can be used in lieu of %systemd_requires in packages which
          don't use any systemd functionality and are intended to be installed
          in minimal containers without systemd present. This macro provides
          ordering dependecies to ensure that if the package is installed in
          the same rpm transaction as systemd, systemd will be installed before
          the scriptlets for the package are executed, allowing unit presets
          to be handled.

          New macros %_systemdgeneratordir and %_systemdusergeneratordir have
          been added to simplify packaging of generators.

        * The os-release file gained VERSION_CODENAME field for the
          distribution nickname (e.g. VERSION_CODENAME=woody).

        * New udev property UDEV_DISABLE_PERSISTENT_STORAGE_RULES_FLAG=1
          can be set to disable parsing of metadata and the creation
          of persistent symlinks for that device.

        * The v230 change to tag framebuffer devices (/dev/fb*) with "uaccess"
          to make them available to logged-in users has been reverted.

        * Much of the common code of the various systemd components is now
          built into an internal shared library libsystemd-shared-231.so
          (incorporating the systemd version number in the name, to be updated
          with future releases) that the components link to. This should
          decrease systemd footprint both in memory during runtime and on
          disk. Note that the shared library is not for public use, and is
          neither API not ABI stable, but is likely to change with every new
          released update. Packagers need to make sure that binaries
          linking to libsystemd-shared.so are updated in step with the
          library.

        * Configuration for "mkosi" is now part of the systemd
          repository. mkosi is a tool to easily build legacy-free OS images,
          and is available on github: https://github.com/systemd/mkosi. If
          "mkosi" is invoked in the build tree a new raw OS image is generated
          incorporating the systemd sources currently being worked on and a
          clean, fresh distribution installation. The generated OS image may be
          booted up with "systemd-nspawn -b -i", qemu-kvm or on any physcial
          UEFI PC. This functionality is particularly useful to easily test
          local changes made to systemd in a pristine, defined environment. See
          HACKING for details.

[Armin]

I already have a pre-generated tarball if you need it

​http://www.linuxfromscratch.org/~krejzi/systemd/systemd-231.tar.xz

[Douglas R. Reno]

Thanks Armin! :-)