systemctl startup script configuration under CentOS 7

Posted by MasK on Tue, 08 Feb 2022 16:59:40 +0100

Sample script

[Unit]      # Mainly service description
Description=test        # Simple description service    # 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/        # 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/    # The service startup command requires an absolute path
PrivateTmp=true     # Indicates that a separate temporary space is allocated to the service
[Install]  # Multi user

[Unit] module – service description

DescriptionShort description of Unit
DocumentationReference document URI list
Before, AfterStart sequence of Units
RequiresThe dependency required for this Unit to start. If the dependency is "deactivated" or "failed", this Unit will be deactivated
WantsConfigure weaker dependencies than "Requires" – if the listed Unit does not start successfully, the start of the Unit has no impact
ConflictsIf a Unit is already set on other units, "start the former" will "stop the latter" - and vice versa (mutually exclusive)

[Service] module – core area

TypeConfigure 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"
ExecStartSpecify 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
ExecStopSpecifies the "Unit" command to stop when executing
ExecReloadSpecifies the command or script to execute when reloading the Unit
RestartAfter starting this selection, the service will "restart" after "process exit", but the systemctl command will execute "clean stop"
RemainAfterExitIf 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/
    - 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 command line status, this setting is very important
    - -- Graphical user status, dependent on

[Install] module

AliasSpaces separate the list of Unit additional names. Most commands (excluding "systemctl", "systemctl enable") can use aliases instead of the actual Unit name
RequiredBy,WantedByWhen the listed service is started, the service will also be started
Reference: "wants requirements", "Unit]"
AlsoSpecifies the list of units to be enabled or disabled together with Unit when the user runs systemctl enable or systemctl disable

reference resources

Topics: Linux