systemd-system.conf man page
systemd-system.conf, system.conf.d, systemd-user.conf, user.conf.d — System and session service manager configuration files
/etc/systemd/system.conf, /etc/systemd/system.conf.d/*.conf, /run/systemd/system.conf.d/*.conf, /usr/lib/systemd/system.conf.d/*.conf
/etc/systemd/user.conf, /etc/systemd/user.conf.d/*.conf, /run/systemd/user.conf.d/*.conf, /usr/lib/systemd/user.conf.d/*.conf
When run as a system instance, systemd interprets the configuration file system.conf and the files in system.conf.d directories; when run as a user instance, systemd interprets the configuration file user.conf and the files in user.conf.d directories. These configuration files contain a few settings controlling basic manager operations.
Configuration Directories and Precedence
The default configuration is defined during compilation, so a configuration file is only needed when it is necessary to deviate from those defaults. By default, the configuration file in /etc/systemd/ contains commented out entries showing the defaults as a guide to the administrator. This file can be edited to create local overrides.
When packages need to customize the configuration, they can install configuration snippets in /usr/lib/systemd/*.conf.d/. Files in /etc/ are reserved for the local administrator, who may use this logic to override the configuration files installed by vendor packages. The main configuration file is read before any of the configuration directories, and has the lowest precedence; entries in a file in any configuration directory override entries in the single configuration file. Files in the *.conf.d/ configuration subdirectories are sorted by their filename in lexicographic order, regardless of which of the subdirectories they reside in. If multiple files specify the same option, the entry in the file with the lexicographically latest name takes precedence. It is recommended to prefix all filenames in those subdirectories with a two-digit number and a dash, to simplify the ordering of the files.
To disable a configuration file supplied by the vendor, the recommended way is to place a symlink to /dev/null in the configuration directory in /etc/, with the same filename as the vendor configuration file.
All options are configured in the "[Manager]" section:
LogLevel=, LogTarget=, LogColor=, LogLocation=, DumpCore=yes, CrashChangeVT=no, CrashShell=no, CrashReboot=no, ShowStatus=yes, DefaultStandardOutput=journal, DefaultStandardError=inherit
Configures various parameters of basic manager operation. These options may be overridden by the respective command line arguments. See systemd(1) for details about these command line arguments.
Defines what action will be performed if user presses Ctrl-Alt-Delete more than 7 times in 2s. Can be set to "reboot-force", "poweroff-force", "reboot-immediate", "poweroff-immediate" or disabled with "none". Defaults to "reboot-force".
Configures the initial CPU affinity for the init process. Takes a list of CPU indices or ranges separated by either whitespace or commas. CPU ranges are specified by the lower and upper CPU indices separated by a dash.
Configures controllers that shall be mounted in a single hierarchy. By default, systemd will mount all controllers which are enabled in the kernel in individual hierarchies, with the exception of those listed in this setting. Takes a space-separated list of comma-separated controller names, in order to allow multiple joined hierarchies. Defaults to 'cpu,cpuacct'. Pass an empty string to ensure that systemd mounts all controllers in separate hierarchies.
Note that this option is only applied once, at very early boot. If you use an initial RAM disk (initrd) that uses systemd, it might hence be necessary to rebuild the initrd if this option is changed, and make sure the new configuration file is included in it. Otherwise, the initrd might mount the controller hierarchies in a different configuration than intended, and the main system cannot remount them anymore.
Configure the hardware watchdog at runtime and at reboot. Takes a timeout value in seconds (or in other time units if suffixed with "ms", "min", "h", "d", "w"). If RuntimeWatchdogSec= is set to a non-zero value, the watchdog hardware (/dev/watchdog) will be programmed to automatically reboot the system if it is not contacted within the specified timeout interval. The system manager will ensure to contact it at least once in half the specified timeout interval. This feature requires a hardware watchdog device to be present, as it is commonly the case in embedded and server systems. Not all hardware watchdogs allow configuration of the reboot timeout, in which case the closest available timeout is picked. ShutdownWatchdogSec= may be used to configure the hardware watchdog when the system is asked to reboot. It works as a safety net to ensure that the reboot takes place even if a clean reboot attempt times out. By default RuntimeWatchdogSec= defaults to 0 (off), and ShutdownWatchdogSec= to 10min. These settings have no effect if a hardware watchdog is not available.
Controls which capabilities to include in the capability bounding set for PID 1 and its children. See capabilities(7) for details. Takes a whitespace-separated list of capability names as read by cap_from_name(3). Capabilities listed will be included in the bounding set, all others are removed. If the list of capabilities is prefixed with ~, all but the listed capabilities will be included, the effect of the assignment inverted. Note that this option also affects the respective capabilities in the effective, permitted and inheritable capability sets. The capability bounding set may also be individually configured for units using the CapabilityBoundingSet= directive for units, but note that capabilities dropped for PID 1 cannot be regained in individual units, they are lost for good.
Takes a space-separated list of architecture identifiers. Selects from which architectures system calls may be invoked on this system. This may be used as an effective way to disable invocation of non-native binaries system-wide, for example to prohibit execution of 32-bit x86 binaries on 64-bit x86-64 systems. This option operates system-wide, and acts similar to the SystemCallArchitectures= setting of unit files, see systemd.exec(5) for details. This setting defaults to the empty list, in which case no filtering of system calls based on architecture is applied. Known architecture identifiers are "x86", "x86-64", "x32", "arm" and the special identifier "native". The latter implicitly maps to the native architecture of the system (or more specifically, the architecture the system manager was compiled for). Set this setting to "native" to prohibit execution of any non-native binaries. When a binary executes a system call of an architecture that is not listed in this setting, it will be immediately terminated with the SIGSYS signal.
Sets the timer slack in nanoseconds for PID 1, which is inherited by all executed processes, unless overridden individually, for example with the TimerSlackNSec= setting in service units (for details see systemd.exec(5)). The timer slack controls the accuracy of wake-ups triggered by system timers. See prctl(2) for more information. Note that in contrast to most other time span definitions this parameter takes an integer value in nano-seconds if no unit is specified. The usual time units are understood too.
Sets the default accuracy of timer units. This controls the global default for the AccuracySec= setting of timer units, see systemd.timer(5) for details. AccuracySec= set in individual units override the global default for the specific unit. Defaults to 1min. Note that the accuracy of timer units is also affected by the configured timer slack for PID 1, see TimerSlackNSec= above.
DefaultTimeoutStartSec=, DefaultTimeoutStopSec=, DefaultRestartSec=
Configures the default timeouts for starting and stopping of units, as well as the default time to sleep between automatic restarts of units, as configured per-unit in TimeoutStartSec=, TimeoutStopSec= and RestartSec= (for services, see systemd.service(5) for details on the per-unit settings). For non-service units, DefaultTimeoutStartSec= sets the default TimeoutSec= value. DefaultTimeoutStartSec= and DefaultTimeoutStopSec= default to 90s. DefaultRestartSec= defaults to 100ms.
Configure the default unit start rate limiting, as configured per-service by StartLimitIntervalSec= and StartLimitBurst=. See systemd.service(5) for details on the per-service settings. DefaultStartLimitIntervalSec= defaults to 10s. DefaultStartLimitBurst= defaults to 5.
Sets manager environment variables passed to all executed processes. Takes a space-separated list of variable assignments. See environ(7) for details about environment variables.
DefaultEnvironment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"
Sets three variables "VAR1", "VAR2", "VAR3".
DefaultCPUAccounting=, DefaultBlockIOAccounting=, DefaultMemoryAccounting=, DefaultTasksAccounting=
Configure the default resource accounting settings, as configured per-unit by CPUAccounting=, BlockIOAccounting=, MemoryAccounting= and TasksAccounting=. See systemd.resource-control(5) for details on the per-unit settings. DefaultTasksAccounting= defaults to on, the other three settings to off.
Configure the default value for the per-unit TasksMax= setting. See systemd.resource-control(5) for details. This setting applies to all unit types that support resource control settings, with the exception of slice units. Defaults to 15%, which equals 4915 with the kernel's defaults on the host, but might be smaller in OS containers.
DefaultLimitCPU=, DefaultLimitFSIZE=, DefaultLimitDATA=, DefaultLimitSTACK=, DefaultLimitCORE=, DefaultLimitRSS=, DefaultLimitNOFILE=, DefaultLimitAS=, DefaultLimitNPROC=, DefaultLimitMEMLOCK=, DefaultLimitLOCKS=, DefaultLimitSIGPENDING=, DefaultLimitMSGQUEUE=, DefaultLimitNICE=, DefaultLimitRTPRIO=, DefaultLimitRTTIME=
These settings control various default resource limits for units. See setrlimit(2) for details. The resource limit is possible to specify in two formats, value to set soft and hard limits to the same value, or soft:hard to set both limits individually (e.g. DefaultLimitAS=4G:16G). Use the string infinity to configure no limit on a specific resource. The multiplicative suffixes K (=1024), M (=1024*1024) and so on for G, T, P and E may be used for resource limits measured in bytes (e.g. DefaultLimitAS=16G). For the limits referring to time values, the usual time units ms, s, min, h and so on may be used (see systemd.time(7) for details). Note that if no time unit is specified for DefaultLimitCPU= the default unit of seconds is implied, while for DefaultLimitRTTIME= the default unit of microseconds is implied. Also, note that the effective granularity of the limits might influence their enforcement. For example, time limits specified for DefaultLimitCPU= will be rounded up implicitly to multiples of 1s. These settings may be overridden in individual units using the corresponding LimitXXX= directives. Note that these resource limits are only defaults for units, they are not applied to PID 1 itself.
systemd(1), systemd.directives(7), systemd.exec(5), systemd.service(5), environ(7), capabilities(7)
journald.conf(5), kernel-command-line(7), logind.conf(5), systemctl(1), systemd(1), systemd.directives(7), systemd.exec(5), systemd.index(7), systemd.resource-control(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd.timer(5).
system.conf.d(5), systemd-user.conf(5) and user.conf.d(5) are aliases of systemd-system.conf(5).