systemd.exec
Execution environment configuration
- Provided by: systemd (Version: 204-5ubuntu20.31)
- Report a bug
SYNOPSIS
service.service, socket.socket, mount.mount, swap.swap
DESCRIPTION
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:
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"
gives three variables VAR1, VAR2, VAR3.
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 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
systemd(1), systemctl(8), journalctl(8), systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd.mount(5), systemd.kill(5), systemd.directives(7)
NOTES
- 1.
- proc.txt
http://www.kernel.org/doc/Documentation/filesystems/proc.txt
- 2.
- cgroups.txt
http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt
- 3.
- PaxControlGroups
http://www.freedesktop.org/wiki/Software/systemd/PaxControlGroups
- 4.
- sched-design-CFS.txt
http://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt
- 5.
- memory.txt
http://www.kernel.org/doc/Documentation/cgroups/memory.txt
- 6.
- devices.txt
http://www.kernel.org/doc/Documentation/cgroups/devices.txt
- 7.
- blkio-controller.txt
http://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt