OPTIONS¶
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= 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 PrivateUsers= setting is particularly useful in
conjunction with RootDirectory=. For details, see below.
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[1] 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 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. If not set, no PAM session will be opened for the executed processes.
See pam(8) for details.
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=.
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. 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.
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.
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.
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=, 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 only be
written at boot-time, with the
sysctl.d(5) mechanism. Almost no
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. Note that this option does not
prevent kernel tuning through IPC interfaces and external programs. However
InaccessiblePaths= can be used to make some IPC file system objects
inaccessible.
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.
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 or unmounts. See
mount(2) for details. Defaults to
shared. Use
shared to ensure that mounts and unmounts are
propagated from the host to the container 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. 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 in the
user manager instance 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 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) |
@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 |
Kernel module control (init_module(2), delete_module(2)
and related calls) |
@mount |
File system mounting and unmounting (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, namespaces (clone(2), kill(2),
namespaces(7), ... |
@raw-io |
Raw I/O port access (ioperm(2), iopl(2),
pciconfig_read(), ...) |
@resources |
System calls for changing resource limits, memory and scheduling
parameters (setrlimit(2), setpriority(2), ...) |
Note that as new system calls are added to the kernel, additional
system calls might be added to the groups above, so the contents of the sets
may change between systemd versions.
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 architecture
system call filtering is applied.
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 architectures, including x86-64). 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, 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.
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.
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=, RuntimeDirectoryMode=
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).
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 that generate program code dynamically at
runtime, such as JIT execution engines, or programs compiled making use of the
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. 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. 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.