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SYSTEMD.EXEC(5) | systemd.exec | SYSTEMD.EXEC(5) |
NAME¶
systemd.exec - Execution environment configurationSYNOPSIS¶
service.service, socket.socket, mount.mount, swap.swapDESCRIPTION¶
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.OPTIONS¶
WorkingDirectory=Takes an absolute directory path. Sets the
working directory for executed processes. If not set defaults to the root
directory when systemd is running as a system instance and the respective
user's home directory if run as user.
RootDirectory=
Takes an absolute directory path. Sets the
root directory for executed processes, with the chroot(2) system call.
If this is used it must be ensured that the process and all its auxiliary
files are available in the chroot() jail.
User=, Group=
Sets the Unix user or group that the processes
are executed as, respectively. Takes a single user or group name or ID as
argument. If no group is set, the default group of the user is chosen.
SupplementaryGroups=
Sets the supplementary Unix groups the
processes are executed as. This takes a space separated list of group names or
IDs. This option may be specified more than once in which case all listed
groups are set as supplementary groups. When the empty string is assigned the
list of supplementary groups is reset, and all assignments prior to this one
will have no effect. In any way, this option does not override, but extends
the list of supplementary groups configured in the system group database for
the user.
Nice=
Sets the default nice level (scheduling
priority) for executed processes. Takes an integer between -20 (highest
priority) and 19 (lowest priority). See 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[1] for
details.
IOSchedulingClass=
Sets the IO scheduling class for executed
processes. Takes an integer between 0 and 3 or one of the strings none,
realtime, best-effort or idle. See ioprio_set(2)
for details.
IOSchedulingPriority=
Sets the IO scheduling priority for executed
processes. Takes an integer between 0 (highest priority) and 7 (lowest
priority). The available priorities depend on the selected IO scheduling class
(see above). See ioprio_set(2) for details.
CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed
processes. Takes one of other, batch, idle, fifo
or rr. See sched_setscheduler(2) for details.
CPUSchedulingPriority=
Sets the CPU scheduling priority for executed
processes. 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 space-separated list of CPU indexes. This option may be
specified more than once in which case the specificed CPU affinity masks are
merged. If the empty string is assigned the mask is reset, all assignments
prior to this will have no effect. See sched_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, and $ has no special meaning.
If you need to assign a value containing spaces to a variable, use double
quotes (") for the assignment.
Example:
gives three variables VAR1, VAR2, VAR3.
See environ(7) for details about environment variables.
EnvironmentFile=
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"
Similar to Environment= but reads the
environment variables from a text file. The text file should contain new-line
separated variable assignments. Empty lines and lines starting with ; or #
will be ignored, which may be used for commenting. A line ending with a
backslash will be concatenated with the following one, allowing multiline
variable definitions. The parser strips leading and trailing whitespace from
the values of assignments, unless you use double quotes (").
The argument passed should be an absolute file name or wildcard expression,
optionally prefixed with "-", which indicates that if the file does
not exist it won't be read and no error or warning message is logged. This
option may be specified more than once in which case all specified files are
read. If the empty string is assigned to this option the list of file to read
is reset, all prior assignments have no effect.
The files listed with this directive will be read shortly before the process is
executed. Settings from these files override settings made with
Environment=. If the same variable is set twice from these files the
files will be read in the order they are specified and the later setting will
override the earlier setting.
StandardInput=
Controls where file descriptor 0 (STDIN) of
the executed processes is connected to. Takes one of null, tty,
tty-force, tty-fail or socket. If null is selected
standard input will be connected to /dev/null, i.e. all read attempts by the
process will result in immediate EOF. If tty is selected standard input
is connected to a TTY (as configured by TTYPath=, see below) and the
executed process becomes the controlling process of the terminal. If the
terminal is already being controlled by another process the executed process
waits until the current controlling process releases the terminal.
tty-force is similar to tty, but the executed process is
forcefully and immediately made the controlling process of the terminal,
potentially removing previous controlling processes from the terminal.
tty-fail is similar to tty but if the terminal already has a
controlling process start-up of the executed process fails. The socket
option is only valid in socket-activated services, and only when the socket
configuration file (see systemd.socket(5) for details) specifies a
single socket only. If this option is set standard input will be connected to
the socket the service was activated from, which is primarily useful for
compatibility with daemons designed for use with the traditional
inetd(8) daemon. This setting defaults to null.
StandardOutput=
Controls where file descriptor 1 (STDOUT) of
the executed processes is connected to. Takes one of inherit,
null, tty, syslog, kmsg, journal,
syslog+console, kmsg+console, journal+console or
socket. If set to inherit the file descriptor of standard input
is duplicated for standard output. If set to null standard output will
be connected to /dev/null, i.e. everything written to it will be lost. If set
to tty standard output will be connected to a tty (as configured via
TTYPath=, see below). If the TTY is used for output only the executed
process will not become the controlling process of the terminal, and will not
fail or wait for other processes to release the terminal. syslog
connects standard output to the syslog(3) system syslog service.
kmsg connects it with the kernel log buffer which is accessible via
dmesg(1). journal connects it with the journal which is
accessible via journalctl(1) (Note that everything that is written to
syslog or kmsg is implicitly stored in the journal as well, those options are
hence supersets of this one). syslog+console, journal+console
and kmsg+console work similarly but copy the output to the system
console as well. socket connects standard output to a socket from
socket activation, semantics are similar to the respective option of
StandardInput=. This setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which defaults
to journal.
StandardError=
Controls where file descriptor 2 (STDERR) of
the executed processes is connected to. The available options are identical to
those of StandardOutput=, with one exception: if set to inherit
the file descriptor used for standard output is duplicated for standard error.
This setting defaults to the value set with DefaultStandardError= in
systemd-system.conf(5), which defaults to inherit.
TTYPath=
Sets the terminal device node to use if
standard input, output or stderr are connected to a TTY (see above). Defaults
to /dev/console.
TTYReset=
Reset the terminal device specified with
TTYPath= before and after execution. Defaults to no.
TTYVHangup=
Disconnect all clients which have opened the
terminal device specified with TTYPath= before and after execution.
Defaults to no.
TTYVTDisallocate=
If the terminal device specified with
TTYPath= is a virtual console terminal try to deallocate the TTY before
and after execution. This ensures that the screen and scrollback buffer is
cleared. Defaults to no.
SyslogIdentifier=
Sets the process name to prefix log lines sent
to syslog or the kernel log buffer with. If not set defaults to the process
name of the executed process. This option is only useful when
StandardOutput= or StandardError= are set to syslog or
kmsg.
SyslogFacility=
Sets the syslog facility to use when logging
to syslog. One of kern, user, mail, daemon,
auth, syslog, lpr, news, uucp, cron,
authpriv, ftp, local0, local1, local2,
local3, local4, local5, local6 or local7.
See syslog(3) for details. This option is only useful when
StandardOutput= or StandardError= are set to syslog.
Defaults to daemon.
SyslogLevel=
Default syslog level to use when logging to
syslog or the kernel log buffer. One of emerg, alert,
crit, err, warning, notice, info,
debug. See syslog(3) for details. This option is only useful
when StandardOutput= or StandardError= are set to syslog
or kmsg. Note that individual lines output by the daemon might be
prefixed with a different log level which can be used to override the default
log level specified here. The interpretation of these prefixes may be disabled
with SyslogLevelPrefix=, see below. For details see
sd-daemon(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=
These settings control various resource limits
for executed processes. See setrlimit(2) for details. Use the string
infinity to configure no limit on a specific resource.
PAMName=
Sets the PAM service name to set up a session
as. If set the executed process will be registered as a PAM session under the
specified service name. This is only useful in conjunction with the
User= setting. If not set no PAM session will be opened for the
executed processes. See pam(8) for details.
TCPWrapName=
If this is a socket-activated service this
sets the tcpwrap service name to check the permission for the current
connection with. This is only useful in conjunction with socket-activated
services, and stream sockets (TCP) in particular. It has no effect on other
socket types (e.g. datagram/UDP) and on processes unrelated to socket-based
activation. If the tcpwrap verification fails daemon start-up will fail and
the connection is terminated. See tcpd(8) for details. Note that this
option may be used to do access control checks only. Shell commands and
commands described in hosts_options(5) are not supported.
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 as read by
cap_from_name(3), 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, on top of what Capabilities=
does. If this option is not used the capability bounding set is not modified
on process execution, hence no limits on the capabilities of the process are
enforced. This option may appear more than once in which case the bounding
sets are merged. If the empty string is assigned to this option the bounding
set is reset 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.
SecureBits=
Controls the secure bits set for the executed
process. See capabilities(7) for details. Takes a list of strings:
keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot and/or 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.
Capabilities=
Controls the capabilities(7) set for
the executed process. Take a capability string describing the effective,
permitted and inherited capability sets as documented in
cap_from_text(3). Note that these capability sets are usually
influenced by the capabilities attached to the executed file. Due to that
CapabilityBoundingSet= is probably the much more useful setting.
ControlGroup=
Controls the control groups the executed
processes shall be made members of. Takes a space-separated list of cgroup
identifiers. A cgroup identifier is formatted like cpu:/foo/bar, where
"cpu" indicates the kernel control group controller used, and
/foo/bar is the control group path. The controller name and ":" may
be omitted in which case the named systemd control group hierarchy is implied.
Alternatively, the path and ":" may be omitted, in which case the
default control group path for this unit is implied.
This option may be used to place executed processes in arbitrary groups in
arbitrary hierarchies -- which may then be externally configured with
additional execution limits. By default systemd will place all executed
processes in separate per-unit control groups (named after the unit) in the
systemd named hierarchy. This option is primarily intended to place executed
processes in specific paths in specific kernel controller hierarchies. It is
not recommended to manipulate the service control group path in the private
systemd named hierarchy (i.e. name=systemd), and doing this might result in
undefined behaviour. For details about control groups see
cgroups.txt[2].
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.conf(5), 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[3].
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[2]. 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[4].
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[5].
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[6].
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[7].
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[7].
ReadWriteDirectories=, ReadOnlyDirectories=,
InaccessibleDirectories=
Sets up a new file-system name space for
executed processes. These options may be used to limit access a process might
have to the main file-system hierarchy. Each setting takes a space-separated
list of absolute directory paths. Directories listed in
ReadWriteDirectories= are accessible from within the namespace with the
same access rights as from outside. Directories listed in
ReadOnlyDirectories= are accessible for reading only, writing will be
refused even if the usual file access controls would permit this. Directories
listed in InaccessibleDirectories= will be made inaccessible for
processes inside the namespace. Note that restricting access with these
options does not extend to submounts of a directory. You must list submounts
separately in these settings to ensure the same limited access. These options
may be specified more than once in which case all directories listed will have
limited access from within the namespace. If the empty string is assigned to
this option the specific list is reset, and all prior assignments have no
effect.
PrivateTmp=
Takes a boolean argument. If true sets up a
new file system namespace for the executed processes and mounts private /tmp
and /var/tmp directories inside it, that are not shared by processes outside
of the namespace. This is useful to secure access to temporary files of the
process, but makes sharing between processes via /tmp or /var/tmp impossible.
All temporary data created by service will be removed after service is
stopped. Defaults to false.
PrivateNetwork=
Takes a boolean argument. If true sets up a
new network namespace for the executed processes and configures only the
loopback network device lo inside it. No other network devices will be
available to the executed process. This is useful to securely turn off network
access by the executed process. Defaults to false.
MountFlags=
Takes a mount propagation flag: shared,
slave or private, which control whether the file system
namespace set up for this unit's processes will receive or propagate new
mounts. See mount(2) for details. Default to shared.
UtmpIdentifier=
Takes a four character identifier string for
an utmp/wtmp entry for this service. This should only be set for services such
as getty implementations where utmp/wtmp entries must be created and
cleared before and after execution. If the configured string is longer than
four characters it is truncated and the terminal four characters are used.
This setting interprets %I style string replacements. This setting is unset by
default, i.e. no utmp/wtmp entries are created or cleaned up for this
service.
IgnoreSIGPIPE=
Takes a boolean argument. If true causes
SIGPIPE to be ignored in the executed process. Defaults to true, since SIGPIPE
generally is useful only in shell pipelines.
NoNewPrivileges=
Takes a boolean argument. If true ensures that
the service process and all its children can never gain new privileges. This
option is more powerful than the respective secure bits flags (see above), as
it also prohibits UID changes of any kind. This is the simplest, most
effective way to ensure that a process and its children can never elevate
privileges again.
SystemCallFilter=
Takes a space separated list of system call
names. If this setting is used all system calls executed by the unit process
except for the listed ones will result in immediate process termination with
the SIGSYS signal (whitelisting). If the first character of the list is ~ the
effect is inverted: only the listed system calls will result in immediate
process termination (blacklisting). If this option is used
NoNewPrivileges=yes is implied. This feature makes use of the Secure
Computing Mode 2 interfaces of the kernel ('seccomp filtering') and is useful
for enforcing a minimal sandboxing environment. Note that the execve,
rt_sigreturn, sigreturn, exit_group, exit system
calls are implicitly whitelisted and don't need to be listed explicitly. This
option may be specified more than once in which case the filter masks are
merged. If the empty string is assigned the filter is reset, all prior
assignments will have no effect.
SEE ALSO¶
NOTES¶
- 1.
- proc.txt
- 2.
- cgroups.txt
- 3.
- PaxControlGroups
- 4.
- sched-design-CFS.txt
- 5.
- memory.txt
- 6.
- devices.txt
- 7.
- blkio-controller.txt
systemd 204 |