systemd.execsystemdDeveloperLennartPoetteringlennart@poettering.netsystemd.exec5systemd.execExecution environment configurationservice.service,
socket.socket,
mount.mount,
swap.swapDescriptionUnit 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 four unit types. See
systemd.unit5
for the common options of all unit configuration
files, and
systemd.service5,
systemd.socket5,
systemd.swap5
and
systemd.mount5
for more information on the specific unit
configuration files. The execution specific
configuration options are configured in the [Service],
[Socket], [Mount], or [Swap] sections, depending on the unit
type.OptionsWorkingDirectory=Takes an absolute
directory path. Sets the working
directory for executed processes. If
not set defaults to the root directory
when systemd is running as a system
instance and the respective user's
home directory if run as
user.RootDirectory=Takes an absolute
directory path. Sets the root
directory for executed processes, with
the
chroot2
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
or group that the processes are executed
as, respectively. Takes a single user or 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. When the empty
string is assigned the list of
supplementary groups is reset, and all
assignments prior to this one will
have no effect. In any way, 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
setpriority2
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 ,
,
or
. See
ioprio_set2
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_set2
for details.CPUSchedulingPolicy=Sets the CPU
scheduling policy for executed
processes. Takes one of
,
,
,
or
. See
sched_setscheduler2
for details.CPUSchedulingPriority=Sets the CPU
scheduling priority for executed
processes. The available priority
range depends on the selected CPU
scheduling policy (see above). For
real-time scheduling policies an
integer between 1 (lowest priority)
and 99 (highest priority) can be used.
See sched_setscheduler2
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_setscheduler2
for details. Defaults to false.CPUAffinity=Controls the CPU
affinity of the executed
processes. Takes a space-separated
list of CPU indexes. This option may
be specified more than once in which
case the specificed CPU affinity masks
are merged. If the empty string is
assigned the mask is reset, all
assignments prior to this will have no
effect. See
sched_setaffinity2
for details.UMask=Controls the file mode
creation mask. Takes an access mode in
octal notation. See
umask2
for details. Defaults to
0022.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. If the
empty string is assigned to this
option the list of environment
variables is reset, all prior
assignments have no effect.
Variable expansion is not performed
inside the strings, and $ has no special
meaning.
If you need to assign a value containing spaces
to a variable, use double quotes (")
for the assignment.Example:
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"
gives three variables VAR1,
VAR2, VAR3.
See
environ7
for details about environment variables.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. A line
ending with a backslash will be concatenated
with the following one, allowing multiline variable
definitions. The parser strips leading
and trailing whitespace from the values
of assignments, unless you use
double quotes (").The argument passed should be an
absolute file name or wildcard
expression, 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.
This option may be specified more than
once in which case all specified files
are read. If the empty string is
assigned to this option the list of
file to read is reset, all prior
assignments have no effect.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 ,
,
,
or
. If
is selected
standard input will be connected to
/dev/null,
i.e. all read attempts by the process
will result in immediate EOF. If
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.
is similar to ,
but the executed process is forcefully
and immediately made the controlling
process of the terminal, potentially
removing previous controlling
processes from the
terminal. is
similar to but if
the terminal already has a controlling
process start-up of the executed
process fails. The
option is only
valid in socket-activated services,
and only when the socket configuration
file (see
systemd.socket5
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
inetd8
daemon. This setting defaults to
.StandardOutput=Controls where file
descriptor 1 (STDOUT) of the executed
processes is connected to. Takes one
of ,
,
,
,
,
,
,
,
or
. If set to
the file
descriptor of standard input is
duplicated for standard output. If set
to standard
output will be connected to
/dev/null,
i.e. everything written to it will be
lost. If set to
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.
connects standard output to the
syslog3
system syslog
service.
connects it with the kernel log buffer
which is accessible via
dmesg1.
connects it with the journal which is
accessible via
journalctl1
(Note that everything that is written
to syslog or kmsg is implicitly stored
in the journal as well, those options
are hence supersets of this
one). ,
and
work
similarly but copy the output to the
system console as
well. connects
standard output to a socket from
socket activation, semantics are
similar to the respective option of
StandardInput=.
This setting defaults to the value set
with
in
systemd-system.conf5,
which defaults to
.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
the file
descriptor used for standard output is
duplicated for standard error. This
setting defaults to the value set with
in
systemd-system.conf5,
which defaults to
.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.TTYReset=Reset the terminal
device specified with
TTYPath= before and
after execution. Defaults to
no.TTYVHangup=Disconnect all clients
which have opened the terminal device
specified with
TTYPath=
before and after execution. Defaults
to
no.TTYVTDisallocate=If the terminal
device specified with
TTYPath= is a
virtual console terminal try to
deallocate the TTY before and after
execution. This ensures that the
screen and scrollback buffer is
cleared. Defaults to
no.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 or
.SyslogFacility=Sets the syslog
facility to use when logging to
syslog. One of ,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
or
. See
syslog3
for details. This option is only
useful when
StandardOutput= or
StandardError= are
set to .
Defaults to
.SyslogLevel=Default syslog level
to use when logging to syslog or the
kernel log buffer. One of
,
,
,
,
,
,
,
. See
syslog3
for details. This option is only
useful when
StandardOutput= or
StandardError= are
set to or
. 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-daemon3.
Defaults to
.SyslogLevelPrefix=Takes a boolean
argument. If true and
StandardOutput= or
StandardError= are
set to ,
or
, 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-daemon3.
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
prctl2
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.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
setrlimit2
for details. Use the string
infinity to
configure no limit on a specific
resource.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
pam8
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
tcpd8
for details. Note that this option may
be used to do access control checks
only. Shell commands and commands
described in
hosts_options5
are not supported.CapabilityBoundingSet=Controls which
capabilities to include in the
capability bounding set for the
executed process. See
capabilities7
for details. Takes a whitespace
separated list of capability names as
read by
cap_from_name3.
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
effects the respective capabilities in
the effective, permitted and
inheritable capability sets, on top of
what Capabilities=
does. If this option is not used the
capability bounding set is not
modified on process execution, hence
no limits on the capabilities of the
process are enforced. This option may
appear more than once in which case
the bounding sets are merged. If the empty
string is assigned to this option the
bounding set is reset, and all prior
settings have no
effect.SecureBits=Controls the secure
bits set for the executed process. See
capabilities7
for details. Takes a list of strings:
,
,
,
,
and/or
. This
option may appear more than once in
which case the secure bits are
ORed. If the empty string is assigned
to this option the bits are reset to
0.Capabilities=Controls the
capabilities7
set for the executed process. Take a
capability string describing the
effective, permitted and inherited
capability sets as documented in
cap_from_text3.
Note that these capability sets are
usually influenced by the capabilities
attached to the executed file. Due to
that
CapabilityBoundingSet=
is probably the much more useful
setting.ControlGroup=Controls the control
groups the executed processes shall be
made members of. Takes a
space-separated list of cgroup
identifiers. A cgroup identifier is
formatted like
cpu:/foo/bar,
where "cpu" indicates 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 hierarchies -- which may
then be externally configured 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. This option is primarily
intended to place executed processes
in specific paths in specific kernel
controller hierarchies. It is not
recommended to manipulate the service
control group path in the systemd
named hierarchy. For details about
control groups see cgroups.txt.This option may appear more than
once, in which case the list of
control group assignments is
merged. If the same hierarchy gets two
different paths assigned only the
later setting will take effect. If the
empty string is assigned to this
option the list of control group
assignments is reset, all previous
assignments will have no
effect.Note that the list of control
group assignments of a unit is
extended implicitly based on the
settings of
DefaultControllers=
of
systemd-system.conf5,
but a unit's
ControlGroup=
setting for a specific controller
takes precedence.ControlGroupModify=Takes a boolean
argument. If true, the control groups
created for this unit will be owned by
the user specified with
User= (and the
appropriate group), and he/she can create
subgroups as well as add processes to
the group.ControlGroupPersistent=Takes a boolean
argument. If true, the control groups
created for this unit will be marked
to be persistent, i.e. systemd will
not remove them when stopping the
unit. The default is false, meaning
that the control groups will be
removed when the unit is stopped. For
details about the semantics of this
logic see PaxControlGroups.ControlGroupAttribute=Set a specific control
group attribute for executed
processes, and (if needed) add the
executed processes to a cgroup in the
hierarchy of the controller the
attribute belongs to. Takes two
space-separated arguments: the
attribute name (syntax is
cpu.shares where
cpu refers to a
specific controller and
shares to the
attribute name), and the attribute
value. Example:
ControlGroupAttribute=cpu.shares
512. If this option is used
for an attribute that belongs to a
kernel controller hierarchy the unit
is not already configured to be added
to (for example via the
ControlGroup=
option) then the unit will be added to
the controller and the default unit
cgroup path is implied. Thus, using
ControlGroupAttribute=
is in most cases sufficient to make
use of control group enforcements,
explicit
ControlGroup= are
only necessary in case the implied
default control group path for a
service is not desirable. For details
about control group attributes see
cgroups.txt. This
option may appear more than once, in
order to set multiple control group
attributes. If this option is used
multiple times for the same cgroup
attribute only the later setting takes
effect. If the empty string is
assigned to this option the list of
attributes is reset, all previous
cgroup attribute settings have no
effect, including those done with
CPUShares=,
MemoryLimit=,
MemorySoftLimit,
DeviceAllow=,
DeviceDeny=,
BlockIOWeight=,
BlockIOReadBandwidth=,
BlockIOWriteBandwidth=.
CPUShares=Assign the specified
overall CPU time shares to the
processes executed. Takes an integer
value. This controls the
cpu.shares control
group attribute, which defaults to
1024. For details about this control
group attribute see sched-design-CFS.txt.MemoryLimit=MemorySoftLimit=Limit the overall memory usage
of the executed processes to a certain
size. Takes a memory size in bytes. If
the value is suffixed with K, M, G or
T the specified memory size is parsed
as Kilobytes, Megabytes, Gigabytes,
or Terabytes (to the base
1024), respectively. This controls the
memory.limit_in_bytes
and
memory.soft_limit_in_bytes
control group attributes. For details
about these control group attributes
see memory.txt.DeviceAllow=DeviceDeny=Control access to
specific device nodes by the executed processes. Takes two
space separated strings: a device node
path (such as
/dev/null)
followed by a combination of r, w, m
to control reading, writing, or
creating of the specific device node
by the unit, respectively. This controls the
devices.allow
and
devices.deny
control group attributes. For details
about these control group attributes
see devices.txt.BlockIOWeight=Set the default or
per-device overall block IO weight
value for the executed
processes. Takes either a single
weight value (between 10 and 1000) to
set the default block IO weight, or a
space separated pair of a file path
and a weight value to specify the
device specific weight value (Example:
"/dev/sda 500"). The file path may be
specified as path to a block device
node or as any other file in which
case the backing block device of the
file system of the file is
determined. This controls the
blkio.weight and
blkio.weight_device
control group attributes, which
default to 1000. Use this option
multiple times to set weights for
multiple devices. For details about
these control group attributes see
blkio-controller.txt.BlockIOReadBandwidth=BlockIOWriteBandwidth=Set the per-device
overall block IO bandwidth limit for
the executed processes. Takes a space
separated pair of a file path and a
bandwidth value (in bytes per second)
to specify the device specific
bandwidth. The file path may be
specified as path to a block device
node or as any other file in which
case the backing block device of the
file system of the file is determined.
If the bandwidth is suffixed with K, M,
G, or T the specified bandwidth is
parsed as Kilobytes, Megabytes,
Gigabytes, or Terabytes, respectively (Example:
"/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0
5M"). This controls the
blkio.read_bps_device
and
blkio.write_bps_device
control group attributes. Use this
option multiple times to set bandwidth
limits for multiple devices. For
details about these control group
attributes see blkio-controller.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 inaccessible 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. If
the empty string is assigned to this
option the specific list is reset, and
all prior assignments have no
effect.PrivateTmp=Takes a boolean
argument. If true sets up a new file
system namespace for the executed
processes and mounts private
/tmp and
/var/tmp directories
inside it, that are 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 or
/var/tmp
impossible. All temporary data created
by service will be removed after service
is stopped. Defaults to
false.PrivateNetwork=Takes a boolean
argument. If true sets up a new
network namespace for the executed
processes and configures only the
loopback network device
lo inside it. No
other network devices will be
available to the executed process.
This is useful to securely turn off
network access by the executed
process. Defaults to
false.MountFlags=Takes a mount
propagation flag:
,
or
, which
control whether the file system
namespace set up for this unit's
processes will receive or propagate
new mounts. See
mount2
for details. Default to
.UtmpIdentifier=Takes 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.IgnoreSIGPIPE=Takes a boolean
argument. If true causes SIGPIPE to be
ignored in the executed
process. Defaults to true, since
SIGPIPE generally is useful only in
shell pipelines.NoNewPrivileges=Takes a boolean
argument. If true ensures that the
service process and all its children
can never gain new privileges. This
option is more powerful than the respective
secure bits flags (see above), as it
also prohibits UID changes of any
kind. This is the simplest, most
effective way to ensure that a process
and its children can never elevate
privileges again.SystemCallFilter=Takes a space
separated list of system call
names. If this setting is used all
system calls executed by the unit
process except for the listed ones
will result in immediate process
termination with the SIGSYS signal
(whitelisting). If the first character
of the list is ~
the effect is inverted: only the
listed system calls will result in
immediate process termination
(blacklisting). If this option is used
NoNewPrivileges=yes
is implied. This feature makes use of
the Secure Computing Mode 2 interfaces
of the kernel ('seccomp filtering')
and is useful for enforcing a minimal
sandboxing environment. Note that the
execve,
rt_sigreturn,
sigreturn,
exit_group,
exit system calls
are implicitly whitelisted and don't
need to be listed explicitly. This
option may be specified more than once
in which case the filter masks are
merged. If the empty string is
assigned the filter is reset, all
prior assignments will have no
effect.See Alsosystemd1,
systemctl8,
journalctl8,
systemd.unit5,
systemd.service5,
systemd.socket5,
systemd.swap5,
systemd.mount5,
systemd.kill5,
systemd.directives7