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NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | OPTIONS | ENVIRONMENT VARIABLES IN SPAWNED PROCESSES | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD.EXEC(5) systemd.exec SYSTEMD.EXEC(5)
systemd.exec - Execution environment configuration
service.service, socket.socket, mount.mount, swap.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 four
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], or [Swap] sections, depending on the unit type.
In addition, options which control resources through Linux Control
Groups (cgroups) are listed in systemd.resource-control(5). Those
options complement options listed here.
A few execution parameters result in additional, automatic
dependencies to be added.
Units with WorkingDirectory=, RootDirectory= or RootImage= set
automatically gain dependencies of type Requires= and After= on all
mount units required to access the specified paths. This is
equivalent to having them listed explicitly in RequiresMountsFor=.
Similar, units with PrivateTmp= enabled automatically get mount unit
dependencies for all mounts required to access /tmp and /var/tmp.
They will also gain an automatic After= dependency on
systemd-tmpfiles-setup.service(8).
Units whose standard output or error output is connected to journal,
syslog or kmsg (or their combinations with console output, see below)
automatically acquire dependencies of type After= on
systemd-journald.socket.
WorkingDirectory=
Takes a directory path relative to the service's root directory
specified by RootDirectory=, or the special value "~". Sets the
working directory for executed processes. If set to "~", the home
directory of the user specified in User= is used. 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. If the setting is prefixed with the "-" character, a
missing working directory is not considered fatal. If
RootDirectory=/RootImage= is not set, then WorkingDirectory= is
relative to the root of the system running the service manager.
Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).
RootDirectory=
Takes a directory path relative to the host's root directory
(i.e. the root of the system running the service manager). Sets
the root directory for executed processes, with the chroot(2)
system call. If this is used, it must be ensured that the process
binary and all its auxiliary files are available in the chroot()
jail. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).
The MountAPIVFS= and PrivateUsers= settings are particularly
useful in conjunction with RootDirectory=. For details, see
below.
RootImage=
Takes a path to a block device node or regular file as argument.
This call is similar to RootDirectory= however mounts a file
system hierarchy from a block device node or loopback file
instead of a directory. The device node or file system image file
needs to contain a file system without a partition table, or a
file system within an MBR/MS-DOS or GPT partition table with only
a single Linux-compatible partition, or a set of file systems
within a GPT partition table that follows the Discoverable
Partitions Specification[1].
MountAPIVFS=
Takes a boolean argument. If on, a private mount namespace for
the unit's processes is created and the API file systems /proc,
/sys, and /dev are mounted inside of it, unless they are already
mounted. Note that this option has no effect unless used in
conjunction with RootDirectory=/RootImage= as these three mounts
are generally mounted in the host anyway, and unless the root
directory is changed, the private mount namespace will be a 1:1
copy of the host's, and include these three mounts. Note that the
/dev file system of the host is bind mounted if this option is
used without PrivateDevices=. To run the service with a private,
minimal version of /dev/, combine this option with
PrivateDevices=.
User=, Group=
Set the UNIX user or group that the processes are executed as,
respectively. Takes a single user or group name, or numeric ID as
argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root
user (services managed by root's instance of systemd --user), the
default is "root", but User= may be used to specify a different
user. For user services of any other user, switching user
identity is not permitted, hence the only valid setting is the
same user the user's service manager is running as. If no group
is set, the default group of the user is used. This setting does
not affect commands whose command line is prefixed with "+".
DynamicUser=
Takes a boolean parameter. If set, a UNIX user and group pair is
allocated dynamically when the unit is started, and released as
soon as it is stopped. The user and group will not be added to
/etc/passwd or /etc/group, but are managed transiently during
runtime. The nss-systemd(8) glibc NSS module provides integration
of these dynamic users/groups into the system's user and group
databases. The user and group name to use may be configured via
User= and Group= (see above). If these options are not used and
dynamic user/group allocation is enabled for a unit, the name of
the dynamic user/group is implicitly derived from the unit name.
If the unit name without the type suffix qualifies as valid user
name it is used directly, otherwise a name incorporating a hash
of it is used. If a statically allocated user or group of the
configured name already exists, it is used and no dynamic
user/group is allocated. Dynamic users/groups are allocated from
the UID/GID range 61184...65519. It is recommended to avoid this
range for regular system or login users. At any point in time
each UID/GID from this range is only assigned to zero or one
dynamically allocated users/groups in use. However, UID/GIDs are
recycled after a unit is terminated. Care should be taken that
any processes running as part of a unit for which dynamic
users/groups are enabled do not leave files or directories owned
by these users/groups around, as a different unit might get the
same UID/GID assigned later on, and thus gain access to these
files or directories. If DynamicUser= is enabled, RemoveIPC=,
PrivateTmp= are implied. This ensures that the lifetime of IPC
objects and temporary files created by the executed processes is
bound to the runtime of the service, and hence the lifetime of
the dynamic user/group. Since /tmp and /var/tmp are usually the
only world-writable directories on a system this ensures that a
unit making use of dynamic user/group allocation cannot leave
files around after unit termination. Moreover
ProtectSystem=strict and ProtectHome=read-only are implied, thus
prohibiting the service to write to arbitrary file system
locations. In order to allow the service to write to certain
directories, they have to be whitelisted using ReadWritePaths=,
but care must be taken so that UID/GID recycling doesn't create
security issues involving files created by the service. Use
RuntimeDirectory= (see below) in order to assign a writable
runtime directory to a service, owned by the dynamic user/group
and removed automatically when the unit is terminated. Defaults
to off.
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. This does not affect commands prefixed with "+".
RemoveIPC=
Takes a boolean parameter. If set, all System V and POSIX IPC
objects owned by the user and group the processes of this unit
are run as are removed when the unit is stopped. This setting
only has an effect if at least one of User=, Group= and
DynamicUser= are used. It has no effect on IPC objects owned by
the root user. Specifically, this removes System V semaphores, as
well as System V and POSIX shared memory segments and message
queues. If multiple units use the same user or group the IPC
objects are removed when the last of these units is stopped. This
setting is implied if DynamicUser= is set.
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[2] for
details.
IOSchedulingClass=
Sets the I/O 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 I/O scheduling priority for executed processes. Takes an
integer between 0 (highest priority) and 7 (lowest priority). The
available priorities depend on the selected I/O 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. 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_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 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. This option may be specified more
than once, in which case the specified 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_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 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, however, specifier expansion is
possible. The $ character has no special meaning. If you need to
assign a value containing spaces or the equals sign to a
variable, use double quotes (") for the assignment.
Example:
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
gives three variables "VAR1", "VAR2", "VAR3" with the values
"word1 word2", "word3", "$word 5 6".
See environ(7) 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, lines without an "="
separator, or 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 filename or wildcard
expression, optionally prefixed with "-", 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
the process is executed (more specifically, after all processes
from a previous unit state terminated. This means you can
generate these files in one unit state, and read it with this
option in the next).
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.
PassEnvironment=
Pass environment variables from the systemd system manager to
executed processes. Takes a space-separated list of variable
names. This option may be specified more than once, in which case
all listed variables will be set. If the empty string is assigned
to this option, the list of environment variables is reset, all
prior assignments have no effect. Variables that are not set in
the system manager will not be passed and will be silently
ignored.
Variables passed from this setting are overridden by those passed
from Environment= or EnvironmentFile=.
Example:
PassEnvironment=VAR1 VAR2 VAR3
passes three variables "VAR1", "VAR2", "VAR3" with the values set
for those variables in PID1.
See environ(7) for details about environment variables.
StandardInput=
Controls where file descriptor 0 (STDIN) of the executed
processes is connected to. Takes one of null, tty, tty-force,
tty-fail, socket or fd.
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.
The fd option connects the input stream to a single file
descriptor provided by a socket unit. A custom named file
descriptor can be specified as part of this option, after a ":"
(e.g. "fd:foobar"). If no name is specified, "stdin" is assumed
(i.e. "fd" is equivalent to "fd:stdin"). At least one socket
unit defining such name must be explicitly provided via the
Sockets= option, and file descriptor name may differ from the
name of its containing socket unit. If multiple matches are
found, the first one will be used. See FileDescriptorName= in
systemd.socket(5) for more details about named descriptors and
ordering.
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,
journal, syslog, kmsg, journal+console, syslog+console,
kmsg+console, socket or fd.
inherit duplicates the file descriptor of standard input for
standard output.
null connects standard output to /dev/null, i.e. everything
written to it will be lost.
tty connects standard output 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.
journal connects standard output with the journal which is
accessible via journalctl(1). Note that everything that is
written to syslog or kmsg (see below) is implicitly stored in the
journal as well, the specific two options listed below are hence
supersets of this one.
syslog connects standard output to the syslog(3) system syslog
service, in addition to the journal. Note that the journal daemon
is usually configured to forward everything it receives to syslog
anyway, in which case this option is no different from journal.
kmsg connects standard output with the kernel log buffer which is
accessible via dmesg(1), in addition to the journal. The journal
daemon might be configured to send all logs to kmsg anyway, in
which case this option is no different from journal.
journal+console, syslog+console and kmsg+console work in a
similar way as the three options above but copy the output to the
system console as well.
socket connects standard output to a socket acquired via socket
activation. The semantics are similar to the same option of
StandardInput=.
The fd option connects the output stream to a single file
descriptor provided by a socket unit. A custom named file
descriptor can be specified as part of this option, after a ":"
(e.g. "fd:foobar"). If no name is specified, "stdout" is assumed
(i.e. "fd" is equivalent to "fd:stdout"). At least one socket
unit defining such name must be explicitly provided via the
Sockets= option, and file descriptor name may differ from the
name of its containing socket unit. If multiple matches are
found, the first one will be used. See FileDescriptorName= in
systemd.socket(5) for more details about named descriptors and
ordering.
If the standard output (or error output, see below) of a unit is
connected to the journal, syslog or the kernel log buffer, the
unit will implicitly gain a dependency of type After= on
systemd-journald.socket (also see the automatic dependencies
section above).
This setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which defaults
to journal. Note that setting this parameter might result in
additional dependencies to be added to the unit (see above).
StandardError=
Controls where file descriptor 2 (STDERR) of the executed
processes is connected to. The available options are identical to
those of StandardOutput=, with some exceptions: if set to inherit
the file descriptor used for standard output is duplicated for
standard error, while fd operates on the error stream and will
look by default for a descriptor named "stderr".
This setting defaults to the value set with DefaultStandardError=
in systemd-system.conf(5), which defaults to inherit. Note that
setting this parameter might result in additional dependencies to
be added to the unit (see above).
TTYPath=
Sets the terminal device node to use if standard input, output,
or error 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 the logging
system 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, journal
or kmsg (or to the same settings in combination with +console).
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=
The 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(3). Defaults to info.
SyslogLevelPrefix=
Takes a boolean argument. If true and StandardOutput= or
StandardError= are set to syslog, kmsg or journal, 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(3). 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 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=
Set soft and hard limits on various resources for executed
processes. See setrlimit(2) for details on the resource limit
concept. Resource limits may be specified in two formats: either
as single value to set a specific soft and hard limit to the same
value, or as colon-separated pair soft:hard to set both limits
individually (e.g. "LimitAS=4G:16G"). Use the string infinity to
configure no limit on a specific resource. The multiplicative
suffixes K, M, G, T, P and E (to the base 1024) may be used for
resource limits measured in bytes (e.g. LimitAS=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 LimitCPU= the default unit
of seconds is implied, while for LimitRTTIME= 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 LimitCPU= will be rounded up
implicitly to multiples of 1s. For LimitNICE= the value may be
specified in two syntaxes: if prefixed with "+" or "-", the value
is understood as regular Linux nice value in the range -20..19.
If not prefixed like this the value is understood as raw resource
limit parameter in the range 0..40 (with 0 being equivalent to
1).
Note that most process resource limits configured with these
options are per-process, and processes may fork in order to
acquire a new set of resources that are accounted independently
of the original process, and may thus escape limits set. Also
note that LimitRSS= is not implemented on Linux, and setting it
has no effect. Often it is advisable to prefer the resource
controls listed in systemd.resource-control(5) over these
per-process limits, as they apply to services as a whole, may be
altered dynamically at runtime, and are generally more
expressive. For example, MemoryLimit= is a more powerful (and
working) replacement for LimitRSS=.
For system units these resource limits may be chosen freely. For
user units however (i.e. units run by a per-user instance of
systemd(1)), these limits are bound by (possibly more
restrictive) per-user limits enforced by the OS.
Resource limits not configured explicitly for a unit default to
the value configured in the various DefaultLimitCPU=,
DefaultLimitFSIZE=, ... options available in
systemd-system.conf(5), and – if not configured there – the
kernel or per-user defaults, as defined by the OS (the latter
only for user services, see above).
Table 1. Resource limit directives, their equivalent ulimit shell
commands and the unit used
┌─────────────────┬───────────────────┬─────────────────────┐
│Directive │ ulimit equivalent │ Unit │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitCPU= │ ulimit -t │ Seconds │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitFSIZE= │ ulimit -f │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitDATA= │ ulimit -d │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitSTACK= │ ulimit -s │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitCORE= │ ulimit -c │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitRSS= │ ulimit -m │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitNOFILE= │ ulimit -n │ Number of File │
│ │ │ Descriptors │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitAS= │ ulimit -v │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitNPROC= │ ulimit -u │ Number of Processes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitMEMLOCK= │ ulimit -l │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitLOCKS= │ ulimit -x │ Number of Locks │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitSIGPENDING= │ ulimit -i │ Number of Queued │
│ │ │ Signals │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitMSGQUEUE= │ ulimit -q │ Bytes │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitNICE= │ ulimit -e │ Nice Level │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitRTPRIO= │ ulimit -r │ Realtime Priority │
├─────────────────┼───────────────────┼─────────────────────┤
│LimitRTTIME= │ No equivalent │ Microseconds │
└─────────────────┴───────────────────┴─────────────────────┘
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, and is otherwise ignored. If not set, no PAM
session will be opened for the executed processes. See pam(8) for
details.
Note that for each unit making use of this option a PAM session
handler process will be maintained as part of the unit and stays
around as long as the unit is active, to ensure that appropriate
actions can be taken when the unit and hence the PAM session
terminates. This process is named "(sd-pam)" and is an immediate
child process of the unit's main process.
CapabilityBoundingSet=
Controls which capabilities to include in the capability bounding
set for the executed process. See capabilities(7) for details.
Takes a whitespace-separated list of capability names, 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 "~", 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. 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 to the empty capability set, and all
prior settings have no effect. If set to "~" (without any further
argument), the bounding set is reset to the full set of available
capabilities, also undoing any previous settings. This does not
affect commands prefixed with "+".
AmbientCapabilities=
Controls which capabilities to include in the ambient capability
set for the executed process. Takes a whitespace-separated list
of capability names, e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
CAP_SYS_PTRACE. This option may appear more than once in which
case the ambient capability sets are merged. If the list of
capabilities is prefixed with "~", all but the listed
capabilities will be included, the effect of the assignment
inverted. If the empty string is assigned to this option, the
ambient capability set is reset to the empty capability set, and
all prior settings have no effect. If set to "~" (without any
further argument), the ambient capability set is reset to the
full set of available capabilities, also undoing any previous
settings. Note that adding capabilities to ambient capability set
adds them to the process's inherited capability set.
Ambient capability sets are useful if you want to execute a
process as a non-privileged user but still want to give it some
capabilities. Note that in this case option keep-caps is
automatically added to SecureBits= to retain the capabilities
over the user change. AmbientCapabilities= does not affect
commands prefixed with "+".
SecureBits=
Controls the secure bits set for the executed process. Takes a
space-separated combination of options from the following list:
keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot, and noroot-locked. 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. This does not affect commands prefixed with "+".
See capabilities(7) for details.
ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=
Sets up a new file system namespace for executed processes. These
options may be used to limit access a process might have to the
file system hierarchy. Each setting takes a space-separated list
of paths relative to the host's root directory (i.e. the system
running the service manager). Note that if paths contain
symlinks, they are resolved relative to the root directory set
with RootDirectory=/RootImage=.
Paths listed in ReadWritePaths= are accessible from within the
namespace with the same access modes as from outside of it. Paths
listed in ReadOnlyPaths= are accessible for reading only, writing
will be refused even if the usual file access controls would
permit this. Nest ReadWritePaths= inside of ReadOnlyPaths= in
order to provide writable subdirectories within read-only
directories. Use ReadWritePaths= in order to whitelist specific
paths for write access if ProtectSystem=strict is used. Paths
listed in InaccessiblePaths= will be made inaccessible for
processes inside the namespace (along with everything below them
in the file system hierarchy).
Note that restricting access with these options does not extend
to submounts of a directory that are created later on.
Non-directory paths may be specified as well. These options may
be specified more than once, in which case all paths 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.
Paths in ReadWritePaths=, ReadOnlyPaths= and InaccessiblePaths=
may be prefixed with "-", in which case they will be ignored when
they do not exist. If prefixed with "+" the paths are taken
relative to the root directory of the unit, as configured with
RootDirectory=/RootImage=, instead of relative to the root
directory of the host (see above). When combining "-" and "+" on
the same path make sure to specify "-" first, and "+" second.
Note that using this setting will disconnect propagation of
mounts from the service to the host (propagation in the opposite
direction continues to work). This means that this setting may
not be used for services which shall be able to install mount
points in the main mount namespace. Note that the effect of these
settings may be undone by privileged processes. In order to set
up an effective sandboxed environment for a unit it is thus
recommended to combine these settings with either
CapabilityBoundingSet=~CAP_SYS_ADMIN or SystemCallFilter=~@mount.
BindPaths=, BindReadOnlyPaths=
Configures unit-specific bind mounts. A bind mount makes a
particular file or directory available at an additional place in
the unit's view of the file system. Any bind mounts created with
this option are specific to the unit, and are not visible in the
host's mount table. This option expects a whitespace separated
list of bind mount definitions. Each definition consists of a
colon-separated triple of source path, destination path and
option string, where the latter two are optional. If only a
source path is specified the source and destination is taken to
be the same. The option string may be either "rbind" or "norbind"
for configuring a recursive or non-recursive bind mount. If the
destination path is omitted, the option string must be omitted
too.
BindPaths= creates regular writable bind mounts (unless the
source file system mount is already marked read-only), while
BindReadOnlyPaths= creates read-only bind mounts. These settings
may be used more than once, each usage appends to the unit's list
of bind mounts. If the empty string is assigned to either of
these two options the entire list of bind mounts defined prior to
this is reset. Note that in this case both read-only and regular
bind mounts are reset, regardless which of the two settings is
used.
This option is particularly useful when RootDirectory=/RootImage=
is used. In this case the source path refers to a path on the
host file system, while the destination path refers to a path
below the root directory of the unit.
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 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 or /var/tmp impossible. If this is enabled,
all temporary files created by a service in these directories
will be removed after the service is stopped. Defaults to false.
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.unit(5) for details. This setting is
implied if DynamicUser= is set. For this setting the same
restrictions regarding mount propagation and privileges apply as
for ReadOnlyPaths= and related calls, see above. Enabling this
setting has the side effect of adding Requires= and After=
dependencies on all mount units necessary to access /tmp and
/var/tmp. Moreover an implicitly After= ordering on
systemd-tmpfiles-setup.service(8) is added.
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 (as well as the pseudo TTY
subsystem) to it, but no physical devices such as /dev/sda,
system memory /dev/mem, system ports /dev/port and others. This
is useful to securely turn off physical device access by the
executed process. Defaults to false. Enabling this option will
install a system call filter to block low-level I/O system calls
that are grouped in the @raw-io set, will also remove CAP_MKNOD
and CAP_SYS_RAWIO from the capability bounding set for the unit
(see above), and set DevicePolicy=closed (see
systemd.resource-control(5) for details). Note that using this
setting will disconnect propagation of mounts from the service to
the host (propagation in the opposite direction continues to
work). This means that this setting may not be used for services
which shall be able to install mount points in the main mount
namespace. The /dev namespace will be mounted read-only and
'noexec'. The latter may break old programs which try to set up
executable memory by using mmap(2) of /dev/zero instead of using
MAP_ANON. This setting is implied if DynamicUser= is set. For
this setting the same restrictions regarding mount propagation
and privileges apply as for ReadOnlyPaths= and related calls, see
above. If turned on and if running in user mode, or in system
mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied.
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. It is possible to run two or more units within
the same private network namespace by using the JoinsNamespaceOf=
directive, see systemd.unit(5) for details. Note that this option
will disconnect all socket families from the host, this includes
AF_NETLINK and AF_UNIX. The latter has the effect that AF_UNIX
sockets in the abstract socket namespace will become unavailable
to the processes (however, those located in the file system will
continue to be accessible).
PrivateUsers=
Takes a boolean argument. If true, sets up a new user namespace
for the executed processes and configures a minimal user and
group mapping, that maps the "root" user and group as well as the
unit's own user and group to themselves and everything else to
the "nobody" user and group. This is useful to securely detach
the user and group databases used by the unit from the rest of
the system, and thus to create an effective sandbox environment.
All files, directories, processes, IPC objects and other
resources owned by users/groups not equaling "root" or the unit's
own will stay visible from within the unit but appear owned by
the "nobody" user and group. If this mode is enabled, all unit
processes are run without privileges in the host user namespace
(regardless if the unit's own user/group is "root" or not).
Specifically this means that the process will have zero process
capabilities on the host's user namespace, but full capabilities
within the service's user namespace. Settings such as
CapabilityBoundingSet= will affect only the latter, and there's
no way to acquire additional capabilities in the host's user
namespace. Defaults to off.
This setting is particularly useful in conjunction with
RootDirectory=/RootImage=, as the need to synchronize the user
and group databases in the root directory and on the host is
reduced, as the only users and groups who need to be matched are
"root", "nobody" and the unit's own user and group.
ProtectSystem=
Takes a boolean argument or the special values "full" or
"strict". If true, mounts the /usr and /boot directories
read-only for processes invoked by this unit. If set to "full",
the /etc directory is mounted read-only, too. If set to "strict"
the entire file system hierarchy is mounted read-only, except for
the API file system subtrees /dev, /proc and /sys (protect these
directories using PrivateDevices=, ProtectKernelTunables=,
ProtectControlGroups=). This setting ensures that any
modification of the vendor-supplied operating system (and
optionally its configuration, and local mounts) is prohibited for
the service. It is recommended to enable this setting for all
long-running services, unless they are involved with system
updates or need to modify the operating system in other ways. If
this option is used, ReadWritePaths= may be used to exclude
specific directories from being made read-only. This setting is
implied if DynamicUser= is set. For this setting the same
restrictions regarding mount propagation and privileges apply as
for ReadOnlyPaths= and related calls, see above. Defaults to off.
ProtectHome=
Takes a boolean argument or "read-only". If true, the directories
/home, /root and /run/user are made inaccessible and empty for
processes invoked by this unit. If set to "read-only", the three
directories are made read-only instead. It is recommended to
enable this setting for all long-running services (in particular
network-facing ones), to ensure they cannot get access to private
user data, unless the services actually require access to the
user's private data. This setting is implied if DynamicUser= is
set. For this setting the same restrictions regarding mount
propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above.
ProtectKernelTunables=
Takes a boolean argument. If true, kernel variables accessible
through /proc/sys, /sys, /proc/sysrq-trigger,
/proc/latency_stats, /proc/acpi, /proc/timer_stats, /proc/fs and
/proc/irq will be made read-only to all processes of the unit.
Usually, tunable kernel variables should be initialized only at
boot-time, for example with the sysctl.d(5) mechanism. Few
services need to write to these at runtime; it is hence
recommended to turn this on for most services. For this setting
the same restrictions regarding mount propagation and privileges
apply as for ReadOnlyPaths= and related calls, see above.
Defaults to off. If turned on and if running in user mode, or in
system mode, but without the CAP_SYS_ADMIN capability (e.g.
services for which User= is set), NoNewPrivileges=yes is implied.
Note that this option does not prevent indirect changes to kernel
tunables effected by IPC calls to other processes. However,
InaccessiblePaths= may be used to make relevant IPC file system
objects inaccessible. If ProtectKernelTunables= is set,
MountAPIVFS=yes is implied.
ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading will
be denied. This allows to turn off module load and unload
operations on modular kernels. It is recommended to turn this on
for most services that do not need special file systems or extra
kernel modules to work. Default to off. Enabling this option
removes CAP_SYS_MODULE from the capability bounding set for the
unit, and installs a system call filter to block module system
calls, also /usr/lib/modules is made inaccessible. For this
setting the same restrictions regarding mount propagation and
privileges apply as for ReadOnlyPaths= and related calls, see
above. Note that limited automatic module loading due to user
configuration or kernel mapping tables might still happen as side
effect of requested user operations, both privileged and
unprivileged. To disable module auto-load feature please see
sysctl.d(5)kernel.modules_disabled mechanism and
/proc/sys/kernel/modules_disabled documentation. If turned on and
if running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.
ProtectControlGroups=
Takes a boolean argument. If true, the Linux Control Groups (‐
cgroups(7)) hierarchies accessible through /sys/fs/cgroup will be
made read-only to all processes of the unit. Except for container
managers no services should require write access to the control
groups hierarchies; it is hence recommended to turn this on for
most services. For this setting the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above. Defaults to off. If
ProtectControlGroups= is set, MountAPIVFS=yes is implied.
MountFlags=
Takes a mount propagation flag: shared, slave or private, which
control whether mounts in the file system namespace set up for
this unit's processes will receive or propagate mounts and
unmounts. See mount(2) for details. Defaults to shared. Use
shared to ensure that mounts and unmounts are propagated from
systemd's namespace to the service's namespace and vice versa.
Use slave to run processes so that none of their mounts and
unmounts will propagate to the host. Use private to also ensure
that no mounts and unmounts from the host will propagate into the
unit processes' namespace. If this is set to slave or private,
any mounts created by spawned processes will be unmounted after
the completion of the current command line of ExecStartPre=,
ExecStartPost=, ExecStart=, and ExecStopPost=. Note that slave
means that file systems mounted on the host might stay mounted
continuously in the unit's namespace, and thus keep the device
busy. Note that the file system namespace related options
(PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
ProtectKernelTunables=, ProtectControlGroups=, ReadOnlyPaths=,
InaccessiblePaths=, ReadWritePaths=) require that mount and
unmount propagation from the unit's file system namespace is
disabled, and hence downgrade shared to slave.
UtmpIdentifier=
Takes a four character identifier string for an utmp(5) and wtmp
entry for this service. This should only be set for services such
as getty implementations (such as agetty(8)) where utmp/wtmp
entries must be created and cleared before and after execution,
or for services that shall be executed as if they were run by a
getty process (see below). 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.
UtmpMode=
Takes one of "init", "login" or "user". If UtmpIdentifier= is
set, controls which type of utmp(5)/wtmp entries for this service
are generated. This setting has no effect unless UtmpIdentifier=
is set too. If "init" is set, only an INIT_PROCESS entry is
generated and the invoked process must implement a
getty-compatible utmp/wtmp logic. If "login" is set, first an
INIT_PROCESS entry, followed by a LOGIN_PROCESS entry is
generated. In this case, the invoked process must implement a
login(1)-compatible utmp/wtmp logic. If "user" is set, first an
INIT_PROCESS entry, then a LOGIN_PROCESS entry and finally a
USER_PROCESS entry is generated. In this case, the invoked
process may be any process that is suitable to be run as session
leader. Defaults to "init".
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 authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by "-", all errors
will be ignored. This does not affect commands prefixed with "+".
See setexeccon(3) for details.
AppArmorProfile=
Takes a profile name as argument. The process executed by the
unit will switch to this profile when started. Profiles must
already be loaded in the kernel, or the unit will fail. This
result in a non operation if AppArmor is not enabled. If prefixed
by "-", all errors will be ignored. This does not affect commands
prefixed with "+".
SmackProcessLabel=
Takes a SMACK64 security label as argument. The process executed
by the unit will be started under this label and SMACK will
decide whether the process is allowed to run or not, based on it.
The process will continue to run under the label specified here
unless the executable has its own SMACK64EXEC label, in which
case the process will transition to run under that label. When
not specified, the label that systemd is running under is used.
This directive is ignored if SMACK is disabled.
The value may be prefixed by "-", in which case all errors will
be ignored. An empty value may be specified to unset previous
assignments. This does not affect commands prefixed with "+".
IgnoreSIGPIPE=
Takes a boolean argument. If true, causes SIGPIPE to be ignored
in the executed process. Defaults to true because 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
through execve() (e.g. via setuid or setgid bits, or filesystem
capabilities). This is the simplest and most effective way to
ensure that a process and its children can never elevate
privileges again. Defaults to false, but certain settings force
NoNewPrivileges=yes, ignoring the value of this setting. This is
the case when SystemCallFilter=, SystemCallArchitectures=,
RestrictAddressFamilies=, RestrictNamespaces=, PrivateDevices=,
ProtectKernelTunables=, ProtectKernelModules=,
MemoryDenyWriteExecute=, or RestrictRealtime= are specified.
SystemCallFilter=
Takes a space-separated list of system call names. If this
setting is used, all system calls executed by the unit processes
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 running in user mode, or in system mode, but
without the CAP_SYS_ADMIN capability (e.g. setting User=nobody),
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, exit, exit_group, getrlimit,
rt_sigreturn, sigreturn system calls and the system calls for
querying time and sleeping 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 prior
assignments will have no effect. This does not affect commands
prefixed with "+".
Note that on systems supporting multiple ABIs (such as
x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended to
combine this option with SystemCallArchitectures=native or
similar.
Note that strict system call filters may impact execution and
error handling code paths of the service invocation.
Specifically, access to the execve system call is required for
the execution of the service binary — if it is blocked service
invocation will necessarily fail. Also, if execution of the
service binary fails for some reason (for example: missing
service executable), the error handling logic might require
access to an additional set of system calls in order to process
and log this failure correctly. It might be necessary to
temporarily disable system call filters in order to simplify
debugging of such failures.
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. (For
example, if 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.)
As the number of possible system calls is large, predefined sets
of system calls are provided. A set starts with "@" character,
followed by name of the set.
Table 2. Currently predefined system call sets
┌───────────────┬───────────────────────────┐
│Set │ Description │
├───────────────┼───────────────────────────┤
│@basic-io │ System calls for basic │
│ │ I/O: reading, writing, │
│ │ seeking, file descriptor │
│ │ duplication and closing │
│ │ (read(2), write(2), and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@clock │ System calls for changing │
│ │ the system clock (‐ │
│ │ adjtimex(2), │
│ │ settimeofday(2), and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@cpu-emulation │ System calls for CPU │
│ │ emulation functionality │
│ │ (vm86(2) and related │
│ │ calls) │
├───────────────┼───────────────────────────┤
│@debug │ Debugging, performance │
│ │ monitoring and tracing │
│ │ functionality (ptrace(2), │
│ │ perf_event_open(2) and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@file-system │ File system operations: │
│ │ opening, creating files │
│ │ and directories for read │
│ │ and write, renaming and │
│ │ removing them, reading │
│ │ file properties, or │
│ │ creating hard and │
│ │ symbolic links. │
├───────────────┼───────────────────────────┤
│@io-event │ Event loop system calls │
│ │ (poll(2), select(2), │
│ │ epoll(7), eventfd(2) and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@ipc │ Pipes, SysV IPC, POSIX │
│ │ Message Queues and other │
│ │ IPC (mq_overview(7), │
│ │ svipc(7)) │
├───────────────┼───────────────────────────┤
│@keyring │ Kernel keyring access (‐ │
│ │ keyctl(2) and related │
│ │ calls) │
├───────────────┼───────────────────────────┤
│@module │ Loading and unloading of │
│ │ kernel modules (‐ │
│ │ init_module(2), │
│ │ delete_module(2) and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@mount │ Mounting and unmounting │
│ │ of file systems (‐ │
│ │ mount(2), chroot(2), and │
│ │ related calls) │
├───────────────┼───────────────────────────┤
│@network-io │ Socket I/O (including │
│ │ local AF_UNIX): │
│ │ socket(7), unix(7) │
├───────────────┼───────────────────────────┤
│@obsolete │ Unusual, obsolete or │
│ │ unimplemented (‐ │
│ │ create_module(2), │
│ │ gtty(2), ...) │
├───────────────┼───────────────────────────┤
│@privileged │ All system calls which │
│ │ need super-user │
│ │ capabilities (‐ │
│ │ capabilities(7)) │
├───────────────┼───────────────────────────┤
│@process │ Process control, │
│ │ execution, namespaceing │
│ │ operations (clone(2), │
│ │ kill(2), namespaces(7), │
│ │ ... │
├───────────────┼───────────────────────────┤
│@raw-io │ Raw I/O port access (‐ │
│ │ ioperm(2), iopl(2), │
│ │ pciconfig_read(), ...) │
├───────────────┼───────────────────────────┤
│@reboot │ System calls for │
│ │ rebooting and reboot │
│ │ preparation (reboot(2), │
│ │ kexec(), ...) │
├───────────────┼───────────────────────────┤
│@resources │ System calls for changing │
│ │ resource limits, memory │
│ │ and scheduling parameters │
│ │ (setrlimit(2), │
│ │ setpriority(2), ...) │
├───────────────┼───────────────────────────┤
│@swap │ System calls for │
│ │ enabling/disabling swap │
│ │ devices (swapon(2), │
│ │ swapoff(2)) │
└───────────────┴───────────────────────────┘
Note, that as new system calls are added to the kernel,
additional system calls might be added to the groups above.
Contents of the sets may also change between systemd versions. In
addition, the list of system calls depends on the kernel version
and architecture for which systemd was compiled. Use
systemd-analyze syscall-filter to list the actual list of system
calls in each filter.
It is recommended to combine the file system namespacing related
options with SystemCallFilter=~@mount, in order to prohibit the
unit's processes to undo the mappings. Specifically these are the
options PrivateTmp=, PrivateDevices=, ProtectSystem=,
ProtectHome=, ProtectKernelTunables=, ProtectControlGroups=,
ReadOnlyPaths=, InaccessiblePaths= and ReadWritePaths=.
SystemCallErrorNumber=
Takes an "errno" error number name to return when the system call
filter configured with SystemCallFilter= is triggered, instead of
terminating the process immediately. Takes an error name such as
EPERM, EACCES or EUCLEAN. When this setting is not used, or when
the empty string is assigned, the process will be terminated
immediately when the filter is triggered.
SystemCallArchitectures=
Takes a space-separated list of architecture identifiers to
include in the system call filter. The known architecture
identifiers are the same as for ConditionArchitecture= described
in systemd.unit(5), as well as x32, mips64-n32, mips64-le-n32,
and the special identifier native. Only system calls of the
specified architectures will be permitted to processes of this
unit. This is an effective way to disable compatibility with
non-native architectures for processes, for example to prohibit
execution of 32-bit x86 binaries on 64-bit x86-64 systems. The
special native identifier implicitly maps to the native
architecture of the system (or more strictly: to the architecture
the system manager is compiled for). If running in user mode, or
in system mode, but without the CAP_SYS_ADMIN capability (e.g.
setting User=nobody), NoNewPrivileges=yes is implied. Note that
setting this option to a non-empty list implies that native is
included too. By default, this option is set to the empty list,
i.e. no system call architecture filtering is applied.
Note that system call filtering is not equally effective on all
architectures. For example, on x86 filtering of network
socket-related calls is not possible, due to ABI limitations — a
limitation that x86-64 does not have, however. On systems
supporting multiple ABIs at the same time — such as x86/x86-64 —
it is hence recommended to limit the set of permitted system call
architectures so that secondary ABIs may not be used to
circumvent the restrictions applied to the native ABI of the
system. In particular, setting SystemCallFilter=native is a good
choice for disabling non-native ABIs.
System call architectures may also be restricted system-wide via
the SystemCallArchitectures= option in the global configuration.
See systemd-system.conf(5) for details.
RestrictAddressFamilies=
Restricts the set of socket address families accessible to the
processes of this unit. Takes a space-separated list of address
family names to whitelist, such as AF_UNIX, AF_INET or AF_INET6.
When prefixed with ~ the listed address families will be applied
as blacklist, otherwise as whitelist. Note that this restricts
access to the socket(2) system call only. Sockets passed into the
process by other means (for example, by using socket activation
with socket units, see systemd.socket(5)) are unaffected. Also,
sockets created with socketpair() (which creates connected
AF_UNIX sockets only) are unaffected. Note that this option has
no effect on 32-bit x86, s390, s390x, mips, mips-le, ppc, ppc-le,
pcc64, ppc64-le and is ignored (but works correctly on other
ABIs, including x86-64). Note that on systems supporting multiple
ABIs (such as x86/x86-64) it is recommended to turn off
alternative ABIs for services, so that they cannot be used to
circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user
mode, or in system mode, but without the CAP_SYS_ADMIN capability
(e.g. setting User=nobody), NoNewPrivileges=yes is implied. By
default, no restrictions apply, all address families are
accessible to processes. If assigned the empty string, any
previous address familiy restriction changes are undone. This
setting does not affect commands prefixed with "+".
Use this option to limit exposure of processes to remote access,
in particular via exotic and sensitive network protocols, such as
AF_PACKET. Note that in most cases, the local AF_UNIX address
family should be included in the configured whitelist as it is
frequently used for local communication, including for syslog(2)
logging.
RestrictNamespaces=
Restricts access to Linux namespace functionality for the
processes of this unit. For details about Linux namespaces, see
namespaces(7). Either takes a boolean argument, or a
space-separated list of namespace type identifiers. If false (the
default), no restrictions on namespace creation and switching are
made. If true, access to any kind of namespacing is prohibited.
Otherwise, a space-separated list of namespace type identifiers
must be specified, consisting of any combination of: cgroup, ipc,
net, mnt, pid, user and uts. Any namespace type listed is made
accessible to the unit's processes, access to namespace types not
listed is prohibited (whitelisting). By prepending the list with
a single tilda character ("~") the effect may be inverted: only
the listed namespace types will be made inaccessible, all
unlisted ones are permitted (blacklisting). If the empty string
is assigned, the default namespace restrictions are applied,
which is equivalent to false. Internally, this setting limits
access to the unshare(2), clone(2) and setns(2) system calls,
taking the specified flags parameters into account. Note that —
if this option is used — in addition to restricting creation and
switching of the specified types of namespaces (or all of them,
if true) access to the setns() system call with a zero flags
parameter is prohibited. This setting is only supported on x86,
x86-64, mips, mips-le, mips64, mips64-le, mips64-n32,
mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces no
restrictions on other architectures. If running in user mode, or
in system mode, but without the CAP_SYS_ADMIN capability (e.g.
setting User=), NoNewPrivileges=yes is implied.
Personality=
Controls which kernel architecture uname(2) shall report, when
invoked by unit processes. Takes one of the architecture
identifiers x86, x86-64, ppc, ppc-le, ppc64, ppc64-le, s390 or
s390x. Which personality architectures are supported depends on
the system architecture. Usually the 64bit versions of the
various system architectures support their immediate 32bit
personality architecture counterpart, but no others. For example,
x86-64 systems support the x86-64 and x86 personalities but no
others. The personality feature is useful when running 32-bit
services on a 64-bit host system. If not specified, the
personality is left unmodified and thus reflects the personality
of the host system's kernel.
RuntimeDirectory=
Takes a list of directory names. If set, one or more directories
by the specified names will be created below /run (for system
services) or below $XDG_RUNTIME_DIR (for user services) when the
unit is started, and removed when the unit is stopped. The
directories will have the access mode specified in
RuntimeDirectoryMode=, and will be owned by the user and group
specified in User= and Group=. Use this to manage one or more
runtime directories of the unit and bind their lifetime to the
daemon runtime. The specified directory names must be relative,
and may not include a "/", i.e. must refer to simple directories
to create or remove. This is particularly useful for unprivileged
daemons that cannot create runtime directories in /run due to
lack of privileges, and to make sure the runtime directory is
cleaned up automatically after use. For runtime directories that
require more complex or different configuration or lifetime
guarantees, please consider using tmpfiles.d(5).
RuntimeDirectoryMode=
Specifies the access mode of the directories specified in
RuntimeDirectory= as an octal number. Defaults to 0755. See
"Permissions" in path_resolution(7) for a discussion of the
meaning of permission bits.
MemoryDenyWriteExecute=
Takes a boolean argument. If set, attempts to create memory
mappings that are writable and executable at the same time, or to
change existing memory mappings to become executable, or mapping
shared memory segments as executable are prohibited.
Specifically, a system call filter is added that rejects mmap(2)
system calls with both PROT_EXEC and PROT_WRITE set, mprotect(2)
system calls with PROT_EXEC set and shmat(2) system calls with
SHM_EXEC set. Note that this option is incompatible with programs
and libraries that generate program code dynamically at runtime,
including JIT execution engines, executable stacks, and code
"trampoline" feature of various C compilers. This option improves
service security, as it makes harder for software exploits to
change running code dynamically. Note that this feature is fully
available on x86-64, and partially on x86. Specifically, the
shmat() protection is not available on x86. Note that on systems
supporting multiple ABIs (such as x86/x86-64) it is recommended
to turn off alternative ABIs for services, so that they cannot be
used to circumvent the restrictions of this option. Specifically,
it is recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user
mode, or in system mode, but without the CAP_SYS_ADMIN capability
(e.g. setting User=), NoNewPrivileges=yes is implied.
RestrictRealtime=
Takes a boolean argument. If set, any attempts to enable realtime
scheduling in a process of the unit are refused. This restricts
access to realtime task scheduling policies such as SCHED_FIFO,
SCHED_RR or SCHED_DEADLINE. See sched(7) for details about these
scheduling policies. If running in user mode, or in system mode,
but without the CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied. Realtime scheduling policies may
be used to monopolize CPU time for longer periods of time, and
may hence be used to lock up or otherwise trigger
Denial-of-Service situations on the system. It is hence
recommended to restrict access to realtime scheduling to the few
programs that actually require them. Defaults to off.
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 directories 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.conf(5) or on the kernel command
line (see systemd(1) and kernel-command-line(7)).
$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 passwd(5).
$INVOCATION_ID
Contains a randomized, unique 128bit ID identifying each runtime
cycle of the unit, formatted as 32 character hexadecimal string.
A new ID is assigned each time the unit changes from an inactive
state into an activating or active state, and may be used to
identify this specific runtime cycle, in particular in data
stored offline, such as the journal. The same ID is passed to all
processes run as part of the unit.
$XDG_RUNTIME_DIR
The directory for volatile state. Set for the user systemd
instance, and also in user sessions. See pam_systemd(8).
$XDG_SESSION_ID, $XDG_SEAT, $XDG_VTNR
The identifier of the session, the seat name, and virtual
terminal of the session. Set by pam_systemd(8) for login
sessions. $XDG_SEAT and $XDG_VTNR will only be set when attached
to a seat and a tty.
$MAINPID
The PID of the unit's main process if it is known. This is only
set for control processes as invoked by ExecReload= and similar.
$MANAGERPID
The PID of the user systemd instance, set for processes spawned
by it.
$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a service for socket
activation. See sd_listen_fds(3).
$NOTIFY_SOCKET
The socket sd_notify() talks to. See sd_notify(3).
$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive notifications. See
sd_watchdog_enabled(3).
$TERM
Terminal type, set only for units connected to a terminal
(StandardInput=tty, StandardOutput=tty, or StandardError=tty).
See termcap(5).
$JOURNAL_STREAM
If the standard output or standard error output of the executed
processes are connected to the journal (for example, by setting
StandardError=journal) $JOURNAL_STREAM contains the device and
inode numbers of the connection file descriptor, formatted in
decimal, separated by a colon (":"). This permits invoked
processes to safely detect whether their standard output or
standard error output are connected to the journal. The device
and inode numbers of the file descriptors should be compared with
the values set in the environment variable to determine whether
the process output is still connected to the journal. Note that
it is generally not sufficient to only check whether
$JOURNAL_STREAM is set at all as services might invoke external
processes replacing their standard output or standard error
output, without unsetting the environment variable.
This environment variable is primarily useful to allow services
to optionally upgrade their used log protocol to the native
journal protocol (using sd_journal_print(3) and other functions)
if their standard output or standard error output is connected to
the journal anyway, thus enabling delivery of structured metadata
along with logged messages.
$SERVICE_RESULT
Only defined for the service unit type, this environment variable
is passed to all ExecStop= and ExecStopPost= processes, and
encodes the service "result". Currently, the following values are
defined: "protocol" (in case of a protocol violation; if a
service did not take the steps required by its unit
configuration), "timeout" (in case of an operation timeout),
"exit-code" (if a service process exited with a non-zero exit
code; see $EXIT_CODE below for the actual exit code returned),
"signal" (if a service process was terminated abnormally by a
signal; see $EXIT_CODE below for the actual signal used for the
termination), "core-dump" (if a service process terminated
abnormally and dumped core), "watchdog" (if the watchdog
keep-alive ping was enabled for the service but it missed the
deadline), or "resources" (a catch-all condition in case a system
operation failed).
This environment variable is useful to monitor failure or
successful termination of a service. Even though this variable is
available in both ExecStop= and ExecStopPost=, it is usually a
better choice to place monitoring tools in the latter, as the
former is only invoked for services that managed to start up
correctly, and the latter covers both services that failed during
their start-up and those which failed during their runtime.
$EXIT_CODE, $EXIT_STATUS
Only defined for the service unit type, these environment
variables are passed to all ExecStop=, ExecStopPost= processes
and contain exit status/code information of the main process of
the service. For the precise definition of the exit code and
status, see wait(2). $EXIT_CODE is one of "exited", "killed",
"dumped". $EXIT_STATUS contains the numeric exit code formatted
as string if $EXIT_CODE is "exited", and the signal name in all
other cases. Note that these environment variables are only set
if the service manager succeeded to start and identify the main
process of the service.
Table 3. Summary of possible service result variable values
┌──────────────────┬────────────────────┬─────────────────────┐
│$SERVICE_RESULT │ $EXIT_CODE │ $EXIT_STATUS │
├──────────────────┼────────────────────┼─────────────────────┤
│"protocol" │ not set │ not set │
│ ├────────────────────┼─────────────────────┤
│ │ "exited" │ "0" │
├──────────────────┼────────────────────┼─────────────────────┤
│"timeout" │ "killed" │ "TERM", "KILL" │
│ ├────────────────────┼─────────────────────┤
│ │ "exited" │ "0", "1", "2", "3", │
│ │ │ ..., "255" │
├──────────────────┼────────────────────┼─────────────────────┤
│"exit-code" │ "exited" │ "0", "1", "2", "3", │
│ │ │ ..., "255" │
├──────────────────┼────────────────────┼─────────────────────┤
│"signal" │ "killed" │ "HUP", "INT", │
│ │ │ "KILL", ... │
├──────────────────┼────────────────────┼─────────────────────┤
│"core-dump" │ "dumped" │ "ABRT", "SEGV", │
│ │ │ "QUIT", ... │
├──────────────────┼────────────────────┼─────────────────────┤
│"watchdog" │ "dumped" │ "ABRT" │
│ ├────────────────────┼─────────────────────┤
│ │ "killed" │ "TERM", "KILL" │
│ ├────────────────────┼─────────────────────┤
│ │ "exited" │ "0", "1", "2", "3", │
│ │ │ ..., "255" │
├──────────────────┼────────────────────┼─────────────────────┤
│"resources" │ any of the above │ any of the above │
├──────────────────┴────────────────────┼─────────────────────┤
│Note: the process may be also │ │
│terminated by a signal not sent by │ │
│systemd. In particular the process may │ │
│send an arbitrary signal to itself in │ │
│a handler for any of the non-maskable │ │
│signals. Nevertheless, in the │ │
│"timeout" and "watchdog" rows above │ │
│only the signals that systemd sends │ │
│have been included. │ │
└───────────────────────────────────────┴─────────────────────┘
Additional variables may be configured by the following means: for
processes spawned in specific units, use the Environment=,
EnvironmentFile= and PassEnvironment= options above; to specify
variables globally, use DefaultEnvironment= (see
systemd-system.conf(5)) or the kernel option systemd.setenv= (see
systemd(1)). Additional variables may also be set through PAM,
cf. pam_env(8).
systemd(1), systemctl(1), systemd-analyze(1), journalctl(8),
systemd.unit(5), systemd.service(5), systemd.socket(5),
systemd.swap(5), systemd.mount(5), systemd.kill(5),
systemd.resource-control(5), systemd.time(7), systemd.directives(7),
tmpfiles.d(5), exec(3)
1. Discoverable Partitions Specification
https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/
2. proc.txt
https://www.kernel.org/doc/Documentation/filesystems/proc.txt
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2018-02-02.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 234 SYSTEMD.EXEC(5)
Pages that refer to this page: systemd(1), systemd-run(1), sd_bus_creds_get_pid(3), sd_id128_get_machine(3), systemd.kill(5), systemd.mount(5), systemd.resource-control(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd-system.conf(5), systemd.unit(5), tmpfiles.d(5), daemon(7), systemd.directives(7), systemd.index(7), systemd.journal-fields(7), nss-systemd(8), systemd-coredump(8)
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