Sample script
[Unit] # Mainly service description Description=test # Simple description service After=network.target # Describes the service category, indicating that the service needs to be started after the network service is started Before=xxx.service # Indicates that some services need to be started Before they are started. The After and Before fields only involve the start order and do not involve dependencies. [Service] # Core area Type=forking # Indicates the background operation mode. User=user # Set the user for the service to run Group=user # Set user groups for service operation KillMode=control-group # Defines how systemd stops services PIDFile=/usr/local/test/test.pid # Absolute path to store PID Restart=no # Define the restart mode of systemd after the service process exits. The default is not to restart ExecStart=/usr/local/test/bin/startup.sh # The service startup command requires an absolute path PrivateTmp=true # Indicates that a separate temporary space is allocated to the service [Install] WantedBy=multi-user.target # Multi user
[Unit] module – service description
| Option | Description |
|---|---|
| Description | Short description of Unit |
| Documentation | Reference document URI list |
| Before, After | Start sequence of Units |
| Requires | The dependency required for this Unit to start. If the dependency is "deactivated" or "failed", this Unit will be deactivated |
| Wants | Configure weaker dependencies than "Requires" – if the listed Unit does not start successfully, the start of the Unit has no impact |
| Conflicts | If a Unit is already set on other units, "start the former" will "stop the latter" - and vice versa (mutually exclusive) |
[Service] module – core area
| Option | Description |
|---|---|
| Type | Configure the startup type of the Unit process that affects the "ExecStart" function and related options: +simple – by default, the process starting from ExecStart is the main process of the service +forking – the process starting from "ExecStart" generates a child process, which is the main process of the service (after startup, the parent process exits) +oneshot – similar to "simple", but the process exits before starting subsequent Units +dbus – similar to "simple", but subsequent units are started only after the main process obtains the D-Bus name +Notify – similar to "simple", but subsequent units will not be started until a notification message is sent through the "sd_notify() function" +idle – similar to "simple", the actual execution of the service binary will be delayed until all jobs are completed, avoiding the mixing of "state output" and "Shell output of the service" |
| ExecStart | Specify the command or script to execute when starting the device +ExecStartPre and ExecStartPost specify custom commands to execute before and after ExecStart +"Tpye=oneshot" can specify multiple custom commands and then execute them sequentially |
| ExecStop | Specifies the "Unit" command to stop when executing |
| ExecReload | Specifies the command or script to execute when reloading the Unit |
| Restart | After starting this selection, the service will "restart" after "process exit", but the systemctl command will execute "clean stop" |
| RemainAfterExit | If set to True, the service is considered active even if all processes exit Default: False – this is particularly useful if "Type=oneshot" is set |
# Type:
- simple((default)-- with ExecStart Field starts the main process
- forking -- ExecStart Field with fork() Start in mode. At this time, the parent process will exit, and the child process is called the main process (running in the background). [generally set to forking]
- oneshot -- be similar to simple ，Single execution only once, systemd Will wait for him to complete the execution before performing other services
- dubs -- be similar to simple ，But I'll wait D-Bus Start after signal
- notify -- be similar to simple ，After the start-up, a notification signal will be sent, and then systemd Restart other services
- idle -- be similar to simple ，The service will not be started until other tasks are completed
# EnvironmentFile:
- Specify the profile, and "Conjunction number(-)" Combined use -- Exceptions that do not exist in the configuration file can be avoided
# Environment: followed by multiple different Shell variables
- Environment=ES_DATA=/usr/local/elasticsearch/data
- Environment=ES_LOG=/usr/local/elasticsearch/log
- Environment=ES_PID=/usr/local/elasticsearch/data/elasticsearch.pid
- EnvironmentFile=-/usr/local/elasticsearch/xxxx.file
# Conjunction sign -- "(-)":
- Before all startup settings, the added variable fields can be added "Conjunction number"
- express "Suppress errors"，When an error occurs, it does not affect the execution of other commands
- "EnvironmentFile=-/usr/local/elasticsearch/xxxx.file" -- When the file does not exist, no exception will be thrown
# Type of KillMode:
- control-group((default) -- All child processes in the current control group will be killed
- process -- Kill only the main process
- mixed -- The main process will receive "SIGTERM signal"，Child process received "SIGKILL" signal
- none -- No process will be killed, just the execution of the service stop command
# Type of Restart:
- no((default) -- No operation after exit
- on-success -- Only when you exit normally (exit status code 0), will you restart
- on-failure -- Abnormal exit and restart, including signal termination, timeout, etc
- on-abnormal -- only "Terminated by signal" or "overtime"，Will restart
- on-abort -- only "When a signal not captured is received and terminated"，Will restart
- on-watchdog -- Timeout exit before restart
- always -- Ignore "Why quit"，Will restart
# For daemons, on failure is recommended
# RestartSec field:
- express systemd Time to wait before restarting the service: RestartSec: 30 (Company: s)
# Various Exec * fields:
- Exec* The following commands are only accepted "Instruction parameters.." Format, not received "<> | &" And other special characters, many bash Syntax is not supported, if you want to support bash Syntax, need to be set Type=oneshot
- ExecStart -- Command to execute when starting the service
- ExecReload -- Command to execute when restarting the service
- ExecStop -- Command to execute when the service is stopped
- ExecStartPre -- Commands to execute before starting the service
- ExecStopPost -- Command to execute after stopping the service
# WantedBy field:
- multi-user.target -- Multi user command line status, this setting is very important
- graphical.target -- Graphical user status, dependent on multi-user.target
[Install] module
| Option | Description |
|---|---|
| Alias | Spaces separate the list of Unit additional names. Most commands (excluding "systemctl", "systemctl enable") can use aliases instead of the actual Unit name |
| RequiredBy，WantedBy | When the listed service is started, the service will also be started Reference: "wants requirements", "Unit]" |
| Also | Specifies the list of units to be enabled or disabled together with Unit when the user runs systemctl enable or systemctl disable |