User:Johannbg/QA/Systemd/Systemd.exec

Name
systemd.exec — systemd execution environment configuration

Synopsis
systemd.service, systemd.socket, systemd.mount

Description
Unit configuration files for services, sockets and mount points share a subset of configuration options which define the execution environment of spawned processes.

This man page lists the configuration options shared by these three unit types. See systemd.unit(5) for the common options of all unit configuration files, and systemd.service(5), systemd.socket(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] resp. [Mount] section, depending on the unit type.

Options
WorkingDirectory= Takes an absolute directory path. Sets the working directory for executed processes.

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 resp. group the processes are executed as. Takes a single user resp. 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 seperated 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. This option does not override but extend 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.

OOMAdjust= Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes an integer between -17 (to disable OOM killing for this process) and 15 (to make killing of this process under memory pressure very likely). See proc.txt 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. Takes an integer between 1 (lowest priority) and 99 (highest priority). The available priority range depends on the selected CPU scheduling policy (see above). 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-seperated list of CPU indexes. 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 0002.

Environment= Sets environment variables for executed processes. Takes a space-seperated 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. See environ(7) for details.

EnvironmentFile= Similar to Environment= but reads the environment variables from a text file. The text file should contain new-line seperated variable assignments. Empty lines and lines starting with ; or # will be ignored, which may be used for commenting.

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 it is waited until that 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 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 logger. kmsg connects it with the kernel log buffer which is accessible via dmesg(1). socket connects standard output to a socket from socket activation, semantics are similar to the respective option of StandardInput=. This setting defaults to inherit.

StandardError= Controls where file descriptor 2 (STDERR) of the executed processes is connected to. The available options are identical to those of StandardOutput=, whith one exception: if set to inherit the file descriptor used for standard output is duplicated for standard error. This setting 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.

SyslogIdentifer= 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(7). Defaults to info.

SyslogLevelPrefix= Takes a boolean argument. If true and StandardOutput= or StandardError= are set to syslog or kmsg 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(7). 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 value is takes a nano-seconds integer and does not understand any other units.

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.

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.

Capabilities= Controls the capabilities(7) set for the executed process. Take a capability string as described in cap_from_text(3). Note that this capability set is usually influenced by the capabilities attached to the executed file.

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, no-setuid-noroot and/or no-setuid-noroot-locked.

CapabilityBoundingSetDrop= Controls the capability bounding set drop set for the executed process. See capabilities(7) for details. Takes a list of capability names as read by cap_from_name(3).

ControlGroup= Controls the control groups the executed processes shall be made members of. Takes a space-seperated list of cgroup identifiers. A cgroup identifier has a format like cpu:/foo/bar, where "cpu" identifies 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 hierachies -- which can be configured externally with additional execution limits. By default systemd will place all executed processes in seperate per-unit control groups (named after the unit) in the systemd named hierarchy. Since every process can be in one group per hierarchy only overriding the control group path in the named systemd hierarchy will disable automatic placement in the default group. For details about control groups see cgroups.txt.

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-seperated 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 inaccesible for processes inside the namespace. Note that restricting access with these options does not extend to submounts of a directory. You must list submounts seperately in these setttings 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.

PrivateTmp= Takes a boolean argument. If true sets up a new namespace for the executed processes and mounts a private /tmp directory 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 impossible. Defaults to false.

MountFlags= Takes a mount propagation flag: shared, slave or private, which control whether namespaces set up with ReadWriteDirectories=, ReadOnlyDirectories= and InaccessibleDirectories= receive or propagate new mounts from/to the main namespace. See mount(1) for details. Defaults to shared, i.e. the new namespace will both receive new mount points from the main namespace as well as propagate new mounts to it.