systemd-system.conf, system.conf.d, systemd-user.conf, user.conf.d - System and
session service manager configuration files
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.
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. When multiple files specify the
same option, for options which accept just a single value, the entry in the
file with the lexicographically latest name takes precedence. For options
which accept a list of values, entries are collected as they occur in files
sorted lexicographically. It is recommended to prefix all filenames in those
subdirectories with a two-digit number and a dash, to simplify the ordering of
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:
Configures various parameters of basic manager
operation. These options may be overridden by the respective process and
kernel command line arguments. See systemd(1) for details.
Defines what action will be performed if user
presses Ctrl-Alt-Delete more than 7 times in 2s. Can be set to
"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
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.
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.
(7) for details about environment variables.
DefaultEnvironment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"
Sets three variables "VAR1", "VAR2", "VAR3".
Configure the default resource accounting
settings, as configured per-unit by CPUAccounting=,
BlockIOAccounting=, MemoryAccounting=, TasksAccounting=
and IPAccounting=. See systemd.resource-control(5) for details
on the per-unit settings. DefaultTasksAccounting= defaults to on, the
other four 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.
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.