The systemd daemon will look for a number of variables in the environment.
When the variable $SYSTEMD_UNIT_PATH is set, the contents of this variable overrides the unit load path. If $SYSTEMD_UNIT_PATH ends with an empty component (":"), the usual unit load path will be appended to the contents of the variable.
Load path when running in system mode (--system).
/etc/systemd/system
/run/systemd/system
/usr/local/lib/systemd/system
/usr/lib/systemd/system
Load path when running in user mode (--user).
$XDG_CONFIG_HOME/systemd/user or $HOME/.config/systemd/user
/etc/systemd/user
$XDG_RUNTIME_DIR/systemd/user
/run/systemd/user
$XDG_DATA_HOME/systemd/user or $HOME/.local/share/systemd/user
$dir/systemd/user for each $dir in $XDG_DATA_DIRS
$dir/systemd/user for each $dir in $XDG_DATA_DIRS
/usr/local/lib/systemd/user
/usr/lib/systemd/user
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https://www.freedesktop.org/software/systemd/man/systemctl.html
SYSTEMD_EDITOR SYSTEMD_PAGER SYSTEMD_LESS
-
https://www.freedesktop.org/software/systemd/man/systemd.html
$SYSTEMD_LOG_LEVEL - systemd reads the log level from this environment variable. This can be overridden with --log-level=.
$SYSTEMD_LOG_TARGET - systemd reads the log target from this environment variable. This can be overridden with --log-target=.
$SYSTEMD_LOG_COLOR - Controls whether systemd highlights important log messages. This can be overridden with --log-color=.
$SYSTEMD_LOG_LOCATION - Controls whether systemd prints the code location along with log messages. This can be overridden with --log-location=.
$XDG_CONFIG_HOME, $XDG_CONFIG_DIRS, $XDG_DATA_HOME, $XDG_DATA_DIRS - The systemd user manager uses these variables in accordance to the XDG Base Directory specification to find its configuration.
$SYSTEMD_UNIT_PATH - Controls where systemd looks for unit files.
$SYSTEMD_SYSVINIT_PATH - Controls where systemd looks for SysV init scripts.
$SYSTEMD_SYSVRCND_PATH - Controls where systemd looks for SysV init script runlevel link farms.
$SYSTEMD_COLORS - The value must be a boolean. Controls whether colorized output should be generated. This can be specified to override the decision that systemd makes based on $TERM and what the console is connected to.
$SYSTEMD_URLIFY - The value must be a boolean. Controls whether clickable links should be generated in the output for terminal emulators supporting this. This can be specified to override the decision that systemd makes based on $TERM and other conditions.
$LISTEN_PID, $LISTEN_FDS, $LISTEN_FDNAMES - Set by systemd for supervised processes during socket-based activation. See sd_listen_fds(3) for more information.
$NOTIFY_SOCKET - Set by systemd for supervised processes for status and start-up completion notification. See sd_notify(3) for more information.
/etc/systemd/system.conf, /etc/systemd/system.conf.d/*.conf, /run/systemd/system.conf.d/*.conf, /usr/lib/systemd/system.conf.d/*.conf
/etc/systemd/user.conf, /etc/systemd/user.conf.d/*.conf, /run/systemd/user.conf.d/*.conf, /usr/lib/systemd/user.conf.d/*.conf
All options are configured in the "[Manager]" section:
LogLevel=, LogTarget=, LogColor=, LogLocation=, DumpCore=yes, CrashChangeVT=no, CrashShell=no, CrashReboot=no, ShowStatus=yes, DefaultStandardOutput=journal, DefaultStandardError=inherit
CtrlAltDelBurstAction=
CPUAffinity=
NUMAPolicy=
RuntimeWatchdogSec=, RebootWatchdogSec=, KExecWatchdogSec=
WatchdogDevice=
CapabilityBoundingSet=
NoNewPrivileges=
SystemCallArchitectures=
TimerSlackNSec=
StatusUnitFormat=
DefaultTimerAccuracySec=
DefaultTimeoutStartSec=, DefaultTimeoutStopSec=, DefaultTimeoutAbortSec=, DefaultRestartSec=
DefaultStartLimitIntervalSec=, DefaultStartLimitBurst=
DefaultEnvironment=
DefaultCPUAccounting=, DefaultBlockIOAccounting=, DefaultMemoryAccounting=, DefaultTasksAccounting=, DefaultIOAccounting=, DefaultIPAccounting=
DefaultTasksMax=
DefaultLimitCPU=, DefaultLimitFSIZE=, DefaultLimitDATA=, DefaultLimitSTACK=, DefaultLimitCORE=, DefaultLimitRSS=, DefaultLimitNOFILE=, DefaultLimitAS=, DefaultLimitNPROC=, DefaultLimitMEMLOCK=, DefaultLimitLOCKS=, DefaultLimitSIGPENDING=, DefaultLimitMSGQUEUE=, DefaultLimitNICE=, DefaultLimitRTPRIO=, DefaultLimitRTTIME=
DefaultOOMPolicy=
It is a good idea to make the default values configurable which will then be overridden in the actual service unit config.
GuessMainPID=yes
TimeoutStartSec
TmeoutStopSec
TimeoutAbortSec
TimeoutSec # configures both TimeoutStartSec and TimeoutStopSec
TimeoutCleanSec=infinity # "systemctl clean" command
RuntimeMaxSec=
WatchdogSec
SuccessExitStatus
NonBlocking=false
NotifyAccess=none # main,exec,all
Sockets=
FileDescriptorStoreMax=
OOMPolicy=
OOMSCoreAdjust=
WorkingDirectory=
RootDirectory=
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=, LimitRTTIME=
UMask
OOMScoreAdjust
TimerSlackNSec
IgnoreSIGPIPE=true
ProtectSystem, ProtectHome
RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=, ConfigurationDirectory=¶
These options take a whitespace-separated list of directory names. The specified directory names must be relative, and may not include "..". If set, one or more directories by the specified names will be created (including their parents) below the locations defined in the following table, when the unit is started. Also, the corresponding environment variable is defined with the full path of directories. If multiple directories are set, then in the environment variable the paths are concatenated with colon (":").
RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=, LogsDirectoryMode=, ConfigurationDirectoryMode=
The chmod for the mentioned dirs when they need to be created.
RuntimeDirectoryPreserve=no
ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=¶
TemporaryFileSystem
PrivateTmp
PrivateDevices
PrivateNetwork
NetworkNamespacePath
PrivateUsers
ProtectHostname, ProtectKernelTunables, ...
RestrictAddressFamilies, RestrictNamespaces
LockPersonality
Environment, EnvironmentFile, PassEnvironment, UnsetEnvironment
StandardInput, StandardOutput, StandardError StandardInputText=, StandardInputData=
LogLevelMax LogExtraFields LogRateLimitIntervalSec=, LogRateLimitBurst= SyslogIdentifier SyslogFacility SyslogLevel SyslogLevelPrefix