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build-sys: metadata updates for v231 (#3803)

System Internals / systemd - Lennart Poettering [poettering.net] - 25 July 2016 14:49 UTC

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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.

38b383d build-sys: metadata updates for v231 (#3803)
Makefile.am | 6 +++---
NEWS | 36 ++++++++++++++++++------------------
configure.ac | 2 +-
3 files changed, 22 insertions(+), 22 deletions(-)

Upstream: github.com