NEWS: add one more name and adjust location

System Internals / systemd - Zbigniew Jędrzejewski-Szmek [] - 21 December 2018 18:53 EST



- NoNewPrivileges=yes has been set for all long-running services implemented by systemd. Previously, this was problematic due to SELinux (as this would also prohibit the transition from PID1's label to the service's label). This restriction has since been lifted, but an SELinux policy update is required. (See e.g.

- DynamicUser=yes is dropped from systemd-networkd.service, systemd-resolved.service and systemd-timesyncd.service, which was enabled in v239 for systemd-networkd.service and systemd-resolved.service, and since v236 for systemd-timesyncd.service. The users and groups systemd-network, systemd-resolve and systemd-timesync are created by systemd-sysusers again. Distributors or system administrators may need to create these users and groups if they not exist (or need to re-enable DynamicUser= for those units) while upgrading systemd.

- When unit files are loaded from disk, previously systemd would sometimes (depending on the unit loading order) load units from the target path of symlinks in .wants/ or .requires/ directories of other units. This meant that unit could be loaded from different paths depending on whether the unit was requested explicitly or as a dependency of another unit, not honouring the priority of directories in search path. It also meant that it was possible to successfully load and start units which are not found in the unit search path, as long as they were requested as a dependency and linked to from .wants/ or .requires/. The target paths of those symlinks are not used for loading units anymore and the unit file must be found in the search path.

- A new service type has been added: Type=exec. It's very similar to Type=simple but ensures the service manager will wait for both fork() and execve() of the main service binary to complete before proceeding with follow-up units. This is primarily useful so that the manager propagates any errors in the preparation phase of service execution back to the job that requested the unit to be started. For example, consider a service that has ExecStart= set to a file system binary that doesn't exist. With Type=simple starting the unit would be considered instantly successful, as only fork() has to complete successfully and the manager does not wait for execve(), and hence its failure is seen "too late". With the new Type=exec service type starting the unit will fail, as the manager will wait for the execve() and notice its failure, which is then propagated back to the start job.

NOTE: with the next release 241 of systemd we intend to change the systemd-run tool to default to Type=exec for transient services started by it. This should be mostly safe, but in specific corner cases might result in problems, as the systemd-run tool will then block on NSS calls (such as user name look-ups due to User=) done between the fork() and execve(), which under specific circumstances might cause problems. It is recommended to specify "-p Type=simple" explicitly in the few cases where this applies. For regular, non-transient services (i.e. those defined with unit files on disk) we will continue to default to Type=simple.

- The Linux kernel's current default RLIMIT_NOFILE resource limit for userspace processes is set to 1024 (soft) and 4096 (hard). Previously, systemd passed this on unmodified to all processes it forked off. With this systemd release the hard limit systemd passes on is increased to 512K, overriding the kernel's defaults and substantially increasing the number of simultaneous file descriptors unprivileged userspace processes can allocate. Note that the soft limit remains at 1024 for compatibility reasons: the traditional UNIX select() call cannot deal with file descriptors >= 1024 and increasing the soft limit globally might thus result in programs unexpectedly allocating a high file descriptor and thus failing abnormally when attempting to use it with select() (of course, programs shouldn't use select() anymore, and prefer poll()/epoll, but the call unfortunately remains undeservedly popular at this time). This change reflects the fact that file descriptor handling in the Linux kernel has been optimized in more recent kernels and allocating large numbers of them should be much cheaper both in memory and in performance than it used to be. Programs that want to take benefit of the increased limit have to "opt-in" into high file descriptors explicitly by raising their soft limit. Of course, when they do that they must acknowledge that they cannot use select() anymore (and neither can any shared library they use — or any shared library used by any shared library they use and so on). Which default hard limit is most appropriate is of course hard to decide. However, given reports that ~300K file descriptors are used in real-life applications we believe 512K is sufficiently high as new default for now. Note that there are also reports that using very high hard limits (e.g. 1G) is problematic: some software allocates large arrays with one element for each potential file descriptor (Java, …) — a high hard limit thus triggers excessively large memory allocations in these applications. Hopefully, the new default of 512K is a good middle ground: higher than what real-life applications currently need, and low enough for avoid triggering excessively large allocations in problematic software. (And yes, somebody should fix Java.)

- The fs.nr_open and fs.file-max sysctls are now automatically bumped to the highest possible values, as separate accounting of file descriptors is no longer necessary, as memcg tracks them correctly as part of the memory accounting anyway. Thus, from the four limits on file descriptors currently enforced (fs.file-max, fs.nr_open, RLIMIT_NOFILE hard, RLIMIT_NOFILE soft) we turn off the first two, and keep only the latter two. A set of build-time options (-Dbump-proc-sys-fs-file-max=no and -Dbump-proc-sys-fs-nr-open=no) has been added to revert this change in behaviour, which might be an option for systems that turn off memcg in the kernel.

- When no /etc/locale.conf file exists (and hence no locale settings are in place), systemd will now use the "C.UTF-8" locale by default, and set LANG= to it. This locale is supported by various distributions including Fedora, with clear indications that upstream glibc is going to make it available too. This locale enables UTF-8 mode by default, which appears appropriate for 2018.

- The "net.ipv4.conf.all.rp_filter" sysctl will now be set to 2 by default. This effectively switches the RFC3704 Reverse Path filtering from Strict mode to Loose mode. This is more appropriate for hosts that have multiple links with routes to the same networks (e.g. a client with a Wi-Fi and Ethernet both connected to the internet).

Consult the kernel documentation for details on this sysctl:

- CPUAccounting=yes no longer enables the CPU controller when using kernel 4.15+ and the unified cgroup hierarchy, as required accounting statistics are now provided independently from the CPU controller.

- Support for disabling a particular cgroup controller within a sub-tree has been added through the DisableControllers= directive.

- cgroup_no_v1=all on the kernel command line now also implies using the unified cgroup hierarchy, unless one explicitly passes systemd.unified_cgroup_hierarchy=0 on the kernel command line.

- The new "MemoryMin=" unit file property may now be used to set the memory usage protection limit of processes invoked by the unit. This controls the cgroupsv2 memory.min attribute. Similarly, the new "IODeviceLatencyTargetSec=" property has been added, wrapping the new cgroupsv2 io.latency cgroup property for configuring per-service I/O latency.

- systemd now supports the cgroupsv2 devices BPF logic, as counterpart to the cgroupsv1 "devices" cgroup controller.

- systemd-escape now is able to combine --unescape with --template. It also learnt a new option --instance for extracting and unescaping the instance part of a unit name.

- sd-bus now provides the sd_bus_message_readv() which is similar to sd_bus_message_read() but takes a va_list object. The pair sd_bus_set_method_call_timeout() and sd_bus_get_method_call_timeout() has been added for configuring the default method call timeout to use. sd_bus_error_move() may be used to efficiently move the contents from one sd_bus_error structure to another, invalidating the source. sd_bus_set_close_on_exit() and sd_bus_get_close_on_exit() may be used to control whether a bus connection object is automatically flushed when an sd-event loop is exited.

- When processing classic BSD syslog log messages, journald will now save the original time-stamp string supplied in the new SYSLOG_TIMESTAMP= journal field. This permits consumers to reconstruct the original BSD syslog message more correctly.

- StandardOutput=/StandardError= in service files gained support for new "append:…" parameters, for connecting STDOUT/STDERR of a service to a file, and appending to it.

- The signal to use as last step of killing of unit processes is now configurable. Previously it was hard-coded to SIGKILL, which may now be overridden with the new KillSignal= setting. Note that this is the signal used when regular termination (i.e. SIGTERM) does not suffice. Similarly, the signal used when aborting a program in case of a watchdog timeout may now be configured too (WatchdogSignal=).

- The XDG_SESSION_DESKTOP environment variable may now be configured in the pam_systemd argument line, using the new desktop= switch. This is useful to initialize it properly from a display manager without having to touch C code.

- Most configuration options that previously accepted percentage values now also accept permille values with the '‰' suffix (instead of '%').

- systemd-resolved may now optionally use OpenSSL instead of GnuTLS for DNS-over-TLS.

- systemd-resolved's configuration file resolved.conf gained a new option ReadEtcHosts= which may be used to turn off processing and honoring /etc/hosts entries.

- The "--wait" switch may now be passed to "systemctl is-system-running", in which case the tool will synchronously wait until the system finished start-up.

- hostnamed gained a new bus call to determine the DMI product UUID.

- On x86-64 systemd will now prefer using the RDRAND processor instruction over /dev/urandom whenever it requires randomness that neither has to be crypto-grade nor should be reproducible. This should substantially reduce the amount of entropy systemd requests from the kernel during initialization on such systems, though not reduce it to zero. (Why not zero? systemd still needs to allocate UUIDs and such uniquely, which require high-quality randomness.)

- networkd gained support for Foo-Over-UDP, ERSPAN and ISATAP tunnels. It also gained a new option ForceDHCPv6PDOtherInformation= for forcing the "Other Information" bit in IPv6 RA messages. The bonding logic gained four new options AdActorSystemPriority=, AdUserPortKey=, AdActorSystem= for configuring various 802.3ad aspects, and DynamicTransmitLoadBalancing= for enabling dynamic shuffling of flows. The tunnel logic gained a new IPv6RapidDeploymentPrefix= option for configuring IPv6 Rapid Deployment. The policy rule logic gained four new options IPProtocol=, SourcePort= and DestinationPort=, InvertRule=. The bridge logic gained support for the MulticastToUnicast= option. networkd also gained support for configuring static IPv4 ARP or IPv6 neighbor entries.

- .preset files (as read by 'systemctl preset') may now be used to instantiate services.

- /etc/crypttab now understands the sector-size= option to configure the sector size for an encrypted partition.

- Key material for encrypted disks may now be placed on a formatted medium, and referenced from /etc/crypttab by the UUID of the file system, followed by "=" suffixed by the path to the key file.

- The "collect" udev component has been removed without replacement, as it is neither used nor maintained.

- When the RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=, ConfigurationDirectory= settings are used in a service the executed processes will now receive a set of environment
variables containing the full paths of these directories. Specifically, RUNTIME_DIRECTORY=, STATE_DIRECTORY, CACHE_DIRECTORY, LOGS_DIRECTORY, CONFIGURATION_DIRECTORY are now set if these options are used. Note that these options may be used multiple times per service in which case the resulting paths will be concatenated and separated by colons.

- Predictable interface naming has been extended to cover InfiniBand NICs. They will be exposed with an "ib" prefix.

- tmpfiles.d/ line types may now be suffixed with a '-' character, in which case the respective line failing is ignored.

- .link files may now be used to configure the equivalent to the "ethtool advertise" commands.

- The sd-device.h and sd-hwdb.h APIs are now exported, as an alternative to libudev.h. Previously, the latter was just an internal wrapper around the former, but now these two APIs are exposed directly.

- sd-id128.h gained a new function sd_id128_get_boot_app_specific() which calculates an app-specific boot ID similar to how sd_id128_get_machine_app_specific() generates an app-specific machine ID.

- A new tool systemd-id128 has been added that can be used to determine and generate various 128bit IDs.

- /etc/os-release gained two new standardized fields DOCUMENTATION_URL= and LOGO=.

- systemd-hibernate-resume-generator will now honor the "noresume" kernel command line option, in which case it will bypass resuming from any hibernated image.

- The systemd-sleep.conf configuration file gained new options AllowSuspend=, AllowHibernation=, AllowSuspendThenHibernate=, AllowHybridSleep= for prohibiting specific sleep modes even if the kernel exports them.

- portablectl is now officially supported and has thus moved to /usr/bin/.

- bootctl learnt the two new commands "set-default" and "set-oneshot" for setting the default boot loader item to boot to (either persistently or only for the next boot). This is currently only compatible with sd-boot, but may be implemented on other boot loaders too, that follow the boot loader interface. The updated interface is now documented here:

- A new kernel command line option systemd.early_core_pattern= is now understood which may be used to influence the core_pattern PID 1 installs during early boot.

- busctl learnt two new options -j and --json= for outputting method call replies, properties and monitoring output in JSON.

- journalctl's JSON output now supports simple ANSI coloring as well as a new "json-seq" mode for generating RFC7464 output.

- Unit files now support the %g/%G specifiers that resolve to the UNIX group/GID of the service manager runs as, similar to the existing %u/%U specifiers that resolve to the UNIX user/UID.

- systemd-logind learnt a new global configuration option UserStopDelaySec= that may be set in logind.conf. It specifies how long the systemd --user instance shall remain started after a user logs out. This is useful to speed up repetitive re-connections of the same user, as it means the user's service manager doesn't have to be stopped/restarted on each iteration, but can be reused between subsequent options. This setting defaults to 10s. systemd-logind also exports two new properties on its Manager D-Bus objects indicating whether the system's lid is currently closed, and whether the system is on AC power.

- systemd gained support for a generic boot counting logic, which generically permits automatic reverting to older boot loader entries if newer updated ones don't work. The boot loader side is implemented in sd-boot, but is kept open for other boot loaders too. For details see:

- The SuccessAction=/FailureAction= unit file settings now learnt two new parameters: "exit" and "exit-force", which result in immediate exiting of the service manager, and are only useful in systemd --user and container environments.

- Unit files gained support for a pair of options FailureActionExitStatus=/SuccessActionExitStatus= for configuring the exit status to use as service manager exit status when SuccessAction=/FailureAction= is set to exit or exit-force.

- A pair of LogRateLimitIntervalSec=/LogRateLimitBurst= per-service options may now be used to configure the log rate limiting applied by journald per-service.

- systemd-analyze gained a new verb "timespan" for parsing and normalizing time span values (i.e. strings like "5min 7s 8us").

- systemd-analyze also gained a new verb "security" for analyzing the security and sand-boxing settings of services in order to determine an "exposure level" for them, indicating whether a service would benefit from more sand-boxing options turned on for them.

- "systemd-analyze syscall-filter" will now also show system calls supported by the local kernel but not included in any of the defined groups.

- .nspawn files now understand the Ephemeral= setting, matching the
--ephemeral command line switch.

- sd-event gained the new APIs sd_event_source_get_floating() and sd_event_source_set_floating() for controlling whether a specific event source is "floating", i.e. destroyed along with the even loop object itself.

- Unit objects on D-Bus gained a new "Refs" property that lists all clients that currently have a reference on the unit (to ensure it is not unloaded).

- The JoinControllers= option in system.conf is no longer supported, as it didn't work correctly, is hard to support properly, is legacy (as the concept only exists on cgroupsv1) and apparently wasn't used.

- Journal messages that are generated whenever a unit enters the failed state are now tagged with a unique MESSAGE_ID. Similarly, messages generated whenever a service process exits are now made recognizable, too. A taged message is also emitted whenever a unit enters the "dead" state on success.

- systemd-run gained a new switch --working-directory= for configuring the working directory of the service to start. A shortcut -d is equivalent, setting the working directory of the service to the current working directory of the invoking program. The new --shell (or just -S) option has been added for invoking the $SHELL of the caller as a service, and implies --pty --same-dir --wait --collect--service-type=exec. Or in other words, "systemd-run -S" is now the quickest way to quickly get an interactive in a fully clean and well-defined system service context.

- machinectl gained a new verb "import-fs" for importing an OS tree from a directory. Moreover, when a directory or tarball is imported and single top-level directory found with the OS itself below the OS tree is automatically mangled and moved one level up.

- systemd-importd will no longer set up an implicit btrfs loop-back file system on /var/lib/machines. If one is already set up, it will continue to be used.

- A new generator "systemd-run-generator" has been added. It will synthesize a unit from one or more program command lines included in the kernel command line. This is very useful in container managers for example:

# systemd-nspawn -i someimage.raw -b'"some command line"'

This will run "systemd-nspawn" on an image, invoke the specified command line and immediately shut down the container again, returning the command line's exit code.

- The block device locking logic is now documented:

- loginctl and machinectl now optionally output the various tables in JSON using the --output= switch. It is our intention to add similar support to systemctl and all other commands.

- udevadm's query and trigger verb now optionally take a .device unit name as argument.

- systemd-udevd's network naming logic now understands a new net.naming-scheme= kernel command line switch, which may be used to pick a specific version of the naming scheme. This helps stabilizing interface names even as systemd/udev are updated and the naming logic is improved.

- sd-id128.h learnt two new auxiliary helpers: sd_id128_is_allf() and SD_ID128_ALLF to test if a 128bit ID is set to all 0xFF bytes, and to initialize one to all 0xFF.

- After loading the SELinux policy systemd will now recursively relabel all files and directories listed in /run/systemd/relabel-extra.d/*.relabel (which should be simple newline separated lists of paths) in addition to the ones it already implicitly relabels in /run, /dev and /sys. After the relabelling is completed the *.relabel files (and /run/systemd/relabel-extra.d/) are removed. This is useful to permit initrds (i.e. code running before the SELinux policy is in effect) to generate files in the host filesystem safely and ensure that the correct label is applied during the transition to the host OS.

- KERNEL API BREAKAGE: Linux kernel 4.18 changed behaviour regarding mknod() handling in user namespaces. Previously mknod() would always fail with EPERM in user namespaces. Since 4.18 mknod() will succeed but device nodes generated that way cannot be opened, and attempts to open them result in EPERM. This breaks the "graceful fallback" logic in systemd's PrivateDevices= sand-boxing option. This option is implemented defensively, so that when systemd detects it runs in a restricted environment (such as a user namespace, or an environment where mknod() is blocked through seccomp or absence of CAP_SYS_MKNOD) where device nodes cannot be created the effect of PrivateDevices= is bypassed (following the logic that 2nd-level sand-boxing is not essential if the system systemd runs in is itself already sand-boxed as a whole). This logic breaks with 4.18 in container managers where user namespacing is used: suddenly PrivateDevices= succeeds setting up a private /dev/ file system containing devices nodes — but when these are opened they don't work.

At this point is is recommended that container managers utilizing user namespaces that intend to run systemd in the payload explicitly block mknod() with seccomp or similar, so that the graceful fallback logic works again.

We are very sorry for the breakage and the requirement to change container configurations for newer kernels. It's purely caused by an incompatible kernel change. The relevant kernel developers have been notified about this userspace breakage quickly, but they chose to ignore it.

1742aae2a NEWS: add one more name and adjust location
NEWS | 76 ++++++++++++++++++++++++++++++++++----------------------------------
1 file changed, 38 insertions(+), 38 deletions(-)


  • Share