systemd.exec — systemd execution environment configuration
systemd.service
,
systemd.socket
,
systemd.mount
,
systemd.swap
Unit configuration files for services, sockets mount points and swap devices share a subset of configuration options which define the execution environment of spawned processes.
This man page lists the configuration options shared by these three unit types. See systemd.unit(5) for the common options of all unit configuration files, and systemd.service(5), systemd.socket(5), systemd.swap(5) and systemd.mount(5) for more information on the specific unit configuration files. The execution specific configuration options are configured in the [Service], [Socket], [Mount] resp. [Swap] section, depending on the unit type.
WorkingDirectory=
Takes an absolute directory path. Sets the working directory for executed processes.
RootDirectory=
Takes an absolute
directory path. Sets the root
directory for executed processes, with
the
chroot(2)
system call. If this is used it must
be ensured that the process and all
its auxiliary files are available in
the chroot()
jail.
User=
, Group=
Sets the Unix user resp. group the processes are executed as. Takes a single user resp. group name or ID as argument. If no group is set the default group of the user is chosen.
SupplementaryGroups=
Sets the supplementary Unix groups the processes are executed as. This takes a space separated list of group names or IDs. This option may be specified more than once in which case all listed groups are set as supplementary groups. This option does not override but extends the list of supplementary groups configured in the system group database for the user.
Nice=
Sets the default nice level (scheduling priority) for executed processes. Takes an integer between -20 (highest priority) and 19 (lowest priority). See setpriority(2) for details.
OOMScoreAdjust=
Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes an integer between -1000 (to disable OOM killing for this process) and 1000 (to make killing of this process under memory pressure very likely). See proc.txt for details.
IOSchedulingClass=
Sets the IO scheduling
class for executed processes. Takes an
integer between 0 and 3 or one of the
strings none
,
realtime
,
best-effort
or
idle
. See
ioprio_set(2)
for details.
IOSchedulingPriority=
Sets the IO scheduling priority for executed processes. Takes an integer between 0 (highest priority) and 7 (lowest priority). The available priorities depend on the selected IO scheduling class (see above). See ioprio_set(2) for details.
CPUSchedulingPolicy=
Sets the CPU
scheduling policy for executed
processes. Takes one of
other
,
batch
,
idle
,
fifo
or
rr
. See
sched_setscheduler(2)
for details.
CPUSchedulingPriority=
Sets the CPU scheduling priority for executed processes. Takes an integer between 1 (lowest priority) and 99 (highest priority). The available priority range depends on the selected CPU scheduling policy (see above). See sched_setscheduler(2) for details.
CPUSchedulingResetOnFork=
Takes a boolean argument. If true elevated CPU scheduling priorities and policies will be reset when the executed processes fork, and can hence not leak into child processes. See sched_setscheduler(2) for details. Defaults to false.
CPUAffinity=
Controls the CPU affinity of the executed processes. Takes a space-separated list of CPU indexes. See sched_setaffinity(2) for details.
UMask=
Controls the file mode creation mask. Takes an access mode in octal notation. See umask(2) for details. Defaults to 0002.
Environment=
Sets environment variables for executed processes. Takes a space-separated list of variable assignments. This option may be specified more than once in which case all listed variables will be set. If the same variable is set twice the later setting will override the earlier setting. See environ(7) for details.
EnvironmentFile=
Similar to
Environment=
but
reads the environment variables from a
text file. The text file should
contain new-line separated variable
assignments. Empty lines and lines
starting with ; or # will be ignored,
which may be used for commenting. The
argument passed should be an absolute
file name, optionally prefixed with
"-", which indicates that if the file
does not exist it won't be read and no
error or warning message is
logged. The files listed with this
directive will be read shortly before
the process is executed. Settings from
these files override settings made
with
Environment=
. If
the same variable is set twice from
these files the files will be read in
the order they are specified and the
later setting will override the
earlier setting.
StandardInput=
Controls where file
descriptor 0 (STDIN) of the executed
processes is connected to. Takes one
of null
,
tty
,
tty-force
,
tty-fail
or
socket
. If
null
is selected
standard input will be connected to
/dev/null
,
i.e. all read attempts by the process
will result in immediate EOF. If
tty
is selected
standard input is connected to a TTY
(as configured by
TTYPath=
, see
below) and the executed process
becomes the controlling process of the
terminal. If the terminal is already
being controlled by another process the
executed process waits until the current
controlling process releases the
terminal.
tty-force
is similar to tty
,
but the executed process is forcefully
and immediately made the controlling
process of the terminal, potentially
removing previous controlling
processes from the
terminal. tty-fail
is
similar to tty
but if
the terminal already has a controlling
process start-up of the executed
process fails. The
socket
option is only
valid in socket-activated services,
and only when the socket configuration
file (see
systemd.socket(5)
for details) specifies a single socket
only. If this option is set standard
input will be connected to the socket
the service was activated from, which
is primarily useful for compatibility
with daemons designed for use with the
traditional
inetd(8)
daemon. This setting defaults to
null
.
StandardOutput=
Controls where file
descriptor 1 (STDOUT) of the executed
processes is connected to. Takes one
of inherit
,
null
,
tty
,
syslog
,
kmsg
,
kmsg+console
,
syslog+console
or
socket
. If set to
inherit
the file
descriptor of standard input is
duplicated for standard output. If set
to null
standard
output will be connected to
/dev/null
,
i.e. everything written to it will be
lost. If set to tty
standard output will be connected to a
tty (as configured via
TTYPath=
, see
below). If the TTY is used for output
only the executed process will not
become the controlling process of the
terminal, and will not fail or wait
for other processes to release the
terminal. syslog
connects standard output to the
syslog(3)
system logger. kmsg
connects it with the kernel log buffer
which is accessible via
dmesg(1). syslog+console
and kmsg+console
work
similarly but copy the output to the
system console as
well. socket
connects
standard output to a socket from
socket activation, semantics are
similar to the respective option of
StandardInput=
.
This setting defaults to
inherit
.
StandardError=
Controls where file
descriptor 2 (STDERR) of the executed
processes is connected to. The
available options are identical to
those of
StandardOutput=
,
with one exception: if set to
inherit
the file
descriptor used for standard output is
duplicated for standard error. This
setting defaults to
inherit
.
TTYPath=
Sets the terminal
device node to use if standard input,
output or stderr are connected to a
TTY (see above). Defaults to
/dev/console
.
SyslogIdentifier=
Sets the process name
to prefix log lines sent to syslog or
the kernel log buffer with. If not set
defaults to the process name of the
executed process. This option is only
useful when
StandardOutput=
or
StandardError=
are
set to syslog
or
kmsg
.
SyslogFacility=
Sets the syslog
facility to use when logging to
syslog. One of kern
,
user
,
mail
,
daemon
,
auth
,
syslog
,
lpr
,
news
,
uucp
,
cron
,
authpriv
,
ftp
,
local0
,
local1
,
local2
,
local3
,
local4
,
local5
,
local6
or
local7
. See
syslog(3)
for details. This option is only
useful when
StandardOutput=
or
StandardError=
are
set to syslog
.
Defaults to
daemon
.
SyslogLevel=
Default syslog level
to use when logging to syslog or the
kernel log buffer. One of
emerg
,
alert
,
crit
,
err
,
warning
,
notice
,
info
,
debug
. See
syslog(3)
for details. This option is only
useful when
StandardOutput=
or
StandardError=
are
set to syslog
or
kmsg
. Note that
individual lines output by the daemon
might be prefixed with a different log
level which can be used to override
the default log level specified
here. The interpretation of these
prefixes may be disabled with
SyslogLevelPrefix=
,
see below. For details see
sd-daemon(7).
Defaults to
info
.
SyslogLevelPrefix=
Takes a boolean
argument. If true and
StandardOutput=
or
StandardError=
are
set to syslog
or
kmsg
log lines
written by the executed process that
are prefixed with a log level will be
passed on to syslog with this log
level set but the prefix removed. If
set to false, the interpretation of
these prefixes is disabled and the
logged lines are passed on as-is. For
details about this prefixing see
sd-daemon(7).
Defaults to true.
TimerSlackNSec=
Sets the timer slack in nanoseconds for the executed processes. The timer slack controls the accuracy of wake-ups triggered by 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 and does not understand any other units.
LimitCPU=
, LimitFSIZE=
, LimitDATA=
, LimitSTACK=
, LimitCORE=
, LimitRSS=
, LimitNOFILE=
, LimitAS=
, LimitNPROC=
, LimitMEMLOCK=
, LimitLOCKS=
, LimitSIGPENDING=
, LimitMSGQUEUE=
, LimitNICE=
, LimitRTPRIO=
, LimitRTTIME=
These settings control various resource limits for executed processes. See setrlimit(2) for details.
PAMName=
Sets the PAM service
name to set up a session as. If set
the executed process will be
registered as a PAM session under the
specified service name. This is only
useful in conjunction with the
User=
setting. If
not set no PAM session will be opened
for the executed processes. See
pam(8)
for details.
TCPWrapName=
If this is a socket-activated service this sets the tcpwrap service name to check the permission for the current connection with. This is only useful in conjunction with socket-activated services, and stream sockets (TCP) in particular. It has no effect on other socket types (e.g. datagram/UDP) and on processes unrelated to socket-based activation. If the tcpwrap verification fails daemon start-up will fail and the connection is terminated. See tcpd(8) for details.
Capabilities=
Controls the capabilities(7) set for the executed process. Take a capability string as described in cap_from_text(3). Note that this capability set is usually influenced by the capabilities attached to the executed file.
SecureBits=
Controls the secure
bits set for the executed process. See
capabilities(7)
for details. Takes a list of strings:
keep-caps
,
keep-caps-locked
,
no-setuid-fixup
,
no-setuid-fixup-locked
,
no-setuid-noroot
and/or
no-setuid-noroot-locked
.
CapabilityBoundingSetDrop=
Controls the capability bounding set drop set for the executed process. See capabilities(7) for details. Takes a list of capability names as read by cap_from_name(3).
ControlGroup=
Controls the control
groups the executed processes shall be
made members of. Takes a
space-separated list of cgroup
identifiers. A cgroup identifier has a
format like
cpu:/foo/bar
,
where "cpu" identifies the kernel
control group controller used, and
/foo/bar
is the
control group path. The controller name
and ":" may be omitted in which case
the named systemd control group
hierarchy is implied. Alternatively,
the path and ":" may be omitted, in
which case the default control group
path for this unit is implied. This
option may be used to place executed
processes in arbitrary groups in
arbitrary hierachies -- which can be
configured externally with additional execution limits. By default
systemd will place all executed
processes in separate per-unit control
groups (named after the unit) in the
systemd named hierarchy. Since every
process can be in one group per
hierarchy only overriding the control group
path in the named systemd hierarchy
will disable automatic placement in
the default group. For details about control
groups see cgroups.txt.
ReadWriteDirectories=
, ReadOnlyDirectories=
, InaccessibleDirectories=
Sets up a new
file-system name space for executed
processes. These options may be used
to limit access a process might have
to the main file-system
hierarchy. Each setting takes a
space-separated list of absolute
directory paths. Directories listed in
ReadWriteDirectories=
are accessible from within the
namespace with the same access rights
as from outside. Directories listed in
ReadOnlyDirectories=
are accessible for reading only,
writing will be refused even if the
usual file access controls would
permit this. Directories listed in
InaccessibleDirectories=
will be made inaccesible for processes
inside the namespace. Note that
restricting access with these options
does not extend to submounts of a
directory. You must list submounts
separately in these settings to
ensure the same limited access. These
options may be specified more than
once in which case all directories
listed will have limited access from
within the
namespace.
PrivateTmp=
Takes a boolean
argument. If true sets up a new
namespace for the executed processes
and mounts a private
/tmp
directory
inside it, that is not shared by
processes outside of the
namespace. This is useful to secure
access to temporary files of the
process, but makes sharing between
processes via
/tmp
impossible. Defaults to false.
MountFlags=
Takes a mount
propagation flag:
shared
,
slave
or
private
, which
control whether namespaces set up with
ReadWriteDirectories=
,
ReadOnlyDirectories=
and
InaccessibleDirectories=
receive or propagate new mounts
from/to the main namespace. See
mount(1)
for details. Defaults to
shared
, i.e. the new
namespace will both receive new mount
points from the main namespace as well
as propagate new mounts to
it.
UtmpIdentifier=
Takes a a four character identifier string for an utmp/wtmp entry for this service. This should only be set for services such as getty implementations where utmp/wtmp entries must be created and cleared before and after execution. If the configured string is longer than four characters it is truncated and the terminal four characters are used. This setting interprets %I style string replacements. This setting is unset by default, i.e. no utmp/wtmp entries are created or cleaned up for this service.