DescriptionUnit configuration files for services, sockets,
- mount points and swap devices share a subset of
+ mount points, and swap devices share a subset of
configuration options which define the execution
environment of spawned processes.
@@ -69,7 +68,7 @@
files, and
systemd.service5,
systemd.socket5,
- systemd.swap5
+ systemd.swap5,
and
systemd.mount5
for more information on the specific unit
@@ -90,7 +89,7 @@
Takes an absolute
directory path. Sets the working
directory for executed processes. If
- not set defaults to the root directory
+ 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
@@ -105,7 +104,7 @@
directory for executed processes, with
the
chroot2
- system call. If this is used it must
+ system call. If this is used, it must
be ensured that the process and all
its auxiliary files are available in
the chroot()
@@ -129,7 +128,7 @@
Sets the supplementary
Unix groups the processes are executed
- as. This takes a space separated list
+ 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
@@ -167,7 +166,7 @@
for this process) and 1000 (to make
killing of this process under memory
pressure very likely). See proc.txt
+ url="https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt
for details.
@@ -234,7 +233,7 @@
CPUSchedulingResetOnFork=Takes a boolean
- argument. If true elevated CPU
+ argument. If true, elevated CPU
scheduling priorities and policies
will be reset when the executed
processes fork, and can hence not leak
@@ -253,7 +252,7 @@
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
+ assigned, the mask is reset, all
assignments prior to this will have no
effect. See
sched_setaffinity2
@@ -281,23 +280,26 @@
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
+ set twice, the later setting will
override the earlier setting. If the
empty string is assigned to this
- option the list of environment
+ 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.
+ inside the strings, however, specifier
+ expansion is possible. The $ character 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"
+ Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
gives three variables VAR1,
- VAR2, VAR3.
+ VAR2, VAR3
+ with the values word1 word2,
+ word3, $word 5 6.
@@ -311,7 +313,7 @@
Environment= but
reads the environment variables from a
text file. The text file should
- contain new-line separated variable
+ contain new-line-separated variable
assignments. Empty lines and lines
starting with ; or # will be ignored,
which may be used for commenting. A line
@@ -323,17 +325,18 @@
double quotes (").The argument passed should be an
- absolute file name or wildcard
+ absolute filename 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.
+ -, which indicates
+ that if the file does not exist, it
+ will not 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
@@ -342,7 +345,7 @@
with
Environment=. If
the same variable is set twice from
- these files the files will be read in
+ these files, the files will be read in
the order they are specified and the
later setting will override the
earlier setting.
@@ -358,19 +361,19 @@
,
or
. If
- is selected
+ 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
+ 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
+ being controlled by another process, the
executed process waits until the current
controlling process releases the
terminal.
@@ -392,7 +395,7 @@
file (see
systemd.socket5
for details) specifies a single socket
- only. If this option is set standard
+ 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
@@ -417,19 +420,19 @@
,
or
. If set to
- the file
+ , the file
descriptor of standard input is
duplicated for standard output. If set
- to standard
+ to , standard
output will be connected to
/dev/null,
i.e. everything written to it will be
- lost. If set to
+ 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
+ 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
@@ -516,7 +519,7 @@
If the terminal
device specified with
TTYPath= is a
- virtual console terminal try to
+ virtual console terminal, try to
deallocate the TTY before and after
execution. This ensures that the
screen and scrollback buffer is
@@ -527,7 +530,7 @@
SyslogIdentifier=Sets the process name
to prefix log lines sent to syslog or
- the kernel log buffer with. If not set
+ the kernel log buffer with. If not set,
defaults to the process name of the
executed process. This option is only
useful when
@@ -671,13 +674,13 @@
PAMName=Sets the PAM service
- name to set up a session as. If set
+ 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
+ not set, no PAM session will be opened
for the executed processes. See
pam8
for details.
@@ -686,7 +689,7 @@
TCPWrapName=If this is a
- socket-activated service this sets the
+ socket-activated service, this sets the
tcpwrap service name to check the
permission for the current connection
with. This is only useful in
@@ -696,7 +699,7 @@
socket types (e.g. datagram/UDP) and
on processes unrelated to socket-based
activation. If the tcpwrap
- verification fails daemon start-up
+ verification fails, daemon start-up
will fail and the connection is
terminated. See
tcpd8
@@ -716,17 +719,16 @@
capability bounding set for the
executed process. See
capabilities7
- for details. Takes a whitespace
- separated list of capability names as
- read by
+ for details. Takes a whitespace-separated
+ list of capability names as read by
cap_from_name3,
- e.g. CAP_SYS_ADMIN
- CAP_DAC_OVERRIDE
- CAP_SYS_PTRACE.
+ e.g. CAP_SYS_ADMIN,
+ CAP_DAC_OVERRIDE,
+ CAP_SYS_PTRACE.
Capabilities listed will be included
in the bounding set, all others are
removed. If the list of capabilities
- is prefixed with ~
+ is prefixed with ~,
all but the listed capabilities will
be included, the effect of the
assignment inverted. Note that this
@@ -735,7 +737,7 @@
permitted and inheritable capability
sets, on top of what
Capabilities=
- does. If this option is not used the
+ 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
@@ -743,11 +745,11 @@
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 to
+ option, the bounding set is reset to
the empty capability set, and all
prior settings have no effect. If set
to ~ (without any
- further argument) the bounding set is
+ further argument), the bounding set is
reset to the full set of available
capabilities, also undoing any
previous settings.
@@ -768,7 +770,7 @@
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
+ to this option, the bits are reset to
0.
@@ -790,288 +792,16 @@
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 private
- systemd named hierarchy
- (i.e. name=systemd),
- and doing this might result in
- undefined behaviour. 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
+ file system namespace for executed
processes. These options may be used
to limit access a process might have
- to the main file-system
+ to the main file system
hierarchy. Each setting takes a
space-separated list of absolute
directory paths. Directories listed in
@@ -1097,22 +827,30 @@
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
+ option, the specific list is reset, and
all prior assignments have no
- effect.
+ effect.
+ Paths in
+ ReadOnlyDirectories=
+ and
+ InaccessibleDirectories=
+ may be prefixed with
+ -, in which case
+ they will be ignored when they do not
+ exist.PrivateTmp=Takes a boolean
- argument. If true sets up a new file
+ 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
+ /var/tmp
+ directories 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
@@ -1120,16 +858,24 @@
/tmp or
/var/tmp
impossible. All temporary data created
- by service will be removed after service
- is stopped. Defaults to
- false.
+ by service will be removed after
+ the service is stopped. Defaults to
+ false. Note that it is possible to run
+ two or more units within the same
+ private /tmp and
+ /var/tmp
+ namespace by using the
+ JoinsNamespaceOf=
+ directive, see
+ systemd.unit5
+ for details.
PrivateNetwork=Takes a boolean
- argument. If true sets up a new
+ argument. If true, sets up a new
network namespace for the executed
processes and configures only the
loopback network device
@@ -1138,6 +884,30 @@
available to the executed process.
This is useful to securely turn off
network access by the executed
+ process. Defaults to false. Note that
+ it is possible to run two or more
+ units within the same private network
+ namespace by using the
+ JoinsNamespaceOf=
+ directive, see
+ systemd.unit5
+ for details.
+
+
+
+ PrivateDevices=
+
+ Takes a boolean
+ argument. If true, sets up a new /dev
+ namespace for the executed processes
+ and only adds API pseudo devices such
+ as /dev/null,
+ /dev/zero or
+ /dev/random to
+ it, but no physical devices such as
+ /dev/sda. This is
+ useful to securely turn off physical
+ device access by the executed
process. Defaults to
false.
@@ -1171,7 +941,7 @@
entries must be created and cleared
before and after execution. If the
configured string is longer than four
- characters it is truncated and the
+ characters, it is truncated and the
terminal four characters are
used. This setting interprets %I style
string replacements. This setting is
@@ -1180,14 +950,31 @@
this service.
+
+ SELinuxContext=
+
+ Set the SELinux
+ security context of the executed
+ process. If set, this will override
+ the automated domain
+ transition. However, the policy still
+ needs to autorize the transition. This
+ directive is ignored if SELinux is
+ disabled. If prefixed by
+ -, all errors will
+ be ignored. See
+ setexeccon3
+ for details.
+
+
IgnoreSIGPIPE=Takes a boolean
- argument. If true causes SIGPIPE to be
+ argument. If true, causes SIGPIPE to be
ignored in the executed
- process. Defaults to true, since
- SIGPIPE generally is useful only in
+ process. Defaults to true because
+ SIGPIPE generally is useful only in
shell pipelines.
@@ -1195,7 +982,7 @@
NoNewPrivileges=Takes a boolean
- argument. If true ensures that the
+ 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
@@ -1210,19 +997,20 @@
SystemCallFilter=
- Takes a space
- separated list of system call
- names. If this setting is used all
+ 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
+ termination with the
+ SIGSYS signal
(whitelisting). If the first character
- of the list is ~
+ 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
+ (blacklisting). If this option is used,
NoNewPrivileges=yes
is implied. This feature makes use of
the Secure Computing Mode 2 interfaces
@@ -1234,19 +1022,164 @@
sigreturn,
exit_group,
exit system calls
- are implicitly whitelisted and don't
+ are implicitly whitelisted and do not
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
+ assigned, the filter is reset, all
prior assignments will have no
- effect.
+ effect.
+
+ If you specify both types of this option
+ (i.e. whitelisting and blacklisting) the first
+ encountered will take precedence and will
+ dictate the default action (termination
+ or approval of a system call). Then the
+ next occurrences of this option will add or
+ delete the listed system calls from the set
+ of the filtered system calls, depending of
+ its type and the default action (e.g. You
+ have started with a whitelisting of
+ read and write
+ and right after it add a blacklisting of
+ write, then
+ write will be removed from the set)
+
+
+ Environment variables in spawned processes
+
+ Processes started by the system are executed in
+ a clean environment in which select variables
+ listed below are set. System processes started by systemd
+ do not inherit variables from PID 1, but processes
+ started by user systemd instances inherit all
+ environment variables from the user systemd instance.
+
+
+
+
+ $PATH
+
+ Colon-separated list
+ of directiories to use when launching
+ executables. Systemd uses a fixed
+ value of
+ /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin.
+
+
+
+
+ $LANG
+
+ Locale. Can be set in
+ locale.conf5
+ or on the kernel command line (see
+ systemd1
+ and
+ kernel-command-line7).
+
+
+
+
+ $USER
+ $LOGNAME
+ $HOME
+ $SHELL
+
+ User name (twice), home
+ directory, and the login shell.
+ The variables are set for the units that
+ have User= set,
+ which includes user
+ systemd instances.
+ See
+ passwd5.
+
+
+
+
+ $XDG_RUNTIME_DIR
+
+ The directory for volatile
+ state. Set for the user systemd
+ instance, and also in user sessions.
+ See
+ pam_systemd8.
+
+
+
+
+ $XDG_SESSION_ID
+ $XDG_SEAT
+ $XDG_VTNR
+
+ The identifier of the
+ session, the seat name, and
+ virtual terminal of the session. Set
+ by
+ pam_systemd8
+ for login sessions.
+ $XDG_SEAT and
+ $XDG_VTNR will
+ only be set when attached to a seat and a
+ tty.
+
+
+
+ $MANAGERPID
+
+ The PID of the user
+ systemd instance,
+ set for processes spawned by it.
+
+
+
+
+ $LISTEN_FDS
+ $LISTEN_PID
+
+ Information about file
+ descriptors passed to a service for
+ socket activation. See
+ sd_listen_fds3.
+
+
+
+
+ $TERM
+
+ Terminal type, set
+ only for units connected to a terminal
+ (StandardInput=tty,
+ StandardOutput=tty,
+ or
+ StandardError=tty).
+ See
+ termcap5.
+
+
+
+
+ Additional variables may be configured by the
+ following means: for processes spawned in specific
+ units, use the Environment= and
+ EnvironmentFile= options above; to
+ specify variables globally, use
+ DefaultEnvironment= (see
+ systemd-system.conf5)
+ or the kernel option
+ systemd.setenv= (see
+ systemd1). Additional
+ variables may also be set through PAM,
+ c.f. pam_env8.
+
+
See Also
@@ -1259,7 +1192,9 @@
systemd.swap5,
systemd.mount5,
systemd.kill5,
- systemd.directives7
+ systemd.resource-control5,
+ systemd.directives7,
+ exec3