systemctl -l_shell的作用

[root@hadoop01 hadoop]# systemctl  --help
systemctl [OPTIONS...] {COMMAND} ...

Query or send control commands to the systemd manager.

  -h --help           Show this help
     --version        Show package version
     --system         Connect to system manager
  -H --host=[USER@]HOST
                      Operate on remote host
  -M --machine=CONTAINER
                      Operate on local container
  -t --type=TYPE      List units of a particular type
     --state=STATE    List units with particular LOAD or SUB or ACTIVE state
  -p --property=NAME  Show only properties by this name
  -a --all            Show all loaded units/properties, including dead/empty
                      ones. To list all units installed on the system, use
                      the 'list-unit-files' command instead.
  -l --full           Don't ellipsize unit names on output
  -r --recursive      Show unit list of host and local containers
     --reverse        Show reverse dependencies with 'list-dependencies'
     --job-mode=MODE  Specify how to deal with already queued jobs, when
                      queueing a new job
     --show-types     When showing sockets, explicitly show their type
  -i --ignore-inhibitors
                      When shutting down or sleeping, ignore inhibitors
     --kill-who=WHO   Who to send signal to
  -s --signal=SIGNAL  Which signal to send
     --now            Start or stop unit in addition to enabling or disabling it
  -q --quiet          Suppress output
     --no-block       Do not wait until operation finished
     --no-wall        Don't send wall message before halt/power-off/reboot
     --no-reload      Don't reload daemon after en-/dis-abling unit files
     --no-legend      Do not print a legend (column headers and hints)
     --no-pager       Do not pipe output into a pager
     --no-ask-password
                      Do not ask for system passwords
     --global         Enable/disable unit files globally
     --runtime        Enable unit files only temporarily until next reboot
  -f --force          When enabling unit files, override existing symlinks
                      When shutting down, execute action immediately
     --preset-mode=   Apply only enable, only disable, or all presets
     --root=PATH      Enable unit files in the specified root directory
  -n --lines=INTEGER  Number of journal entries to show
  -o --output=STRING  Change journal output mode (short, short-iso,
                              short-precise, short-monotonic, verbose,
                              export, json, json-pretty, json-sse, cat)
     --plain          Print unit dependencies as a list instead of a tree

Unit Commands:
  list-units [PATTERN...]         List loaded units
  list-sockets [PATTERN...]       List loaded sockets ordered by address
  list-timers [PATTERN...]        List loaded timers ordered by next elapse
  start NAME...                   Start (activate) one or more units
  stop NAME...                    Stop (deactivate) one or more units
  reload NAME...                  Reload one or more units
  restart NAME...                 Start or restart one or more units
  try-restart NAME...             Restart one or more units if active
  reload-or-restart NAME...       Reload one or more units if possible,
                                  otherwise start or restart
  reload-or-try-restart NAME...   Reload one or more units if possible,
                                  otherwise restart if active
  isolate NAME                    Start one unit and stop all others
  kill NAME...                    Send signal to processes of a unit
  is-active PATTERN...            Check whether units are active
  is-failed PATTERN...            Check whether units are failed
  status [PATTERN...|PID...]      Show runtime status of one or more units
  show [PATTERN...|JOB...]        Show properties of one or more
                                  units/jobs or the manager
  cat PATTERN...                  Show files and drop-ins of one or more units
  set-property NAME ASSIGNMENT... Sets one or more properties of a unit
  help PATTERN...|PID...          Show manual for one or more units
  reset-failed [PATTERN...]       Reset failed state for all, one, or more
                                  units
  list-dependencies [NAME]        Recursively show units which are required
                                  or wanted by this unit or by which this
                                  unit is required or wanted

systemctl [OPTIONS...] {COMMAND} ...

Query or send control commands to the systemd manager.

  -h --help           Show this help
     --version        Show package version
systemctl [OPTIONS...] {COMMAND} ...

systemctl [OPTIONS...] {COMMAND} ...

Query or send control commands to the systemd manager.

  -h --help           Show this help
     --version        Show package version
     --system         Connect to system manager
  -H --host=[USER@]HOST
                      Operate on remote host
  -M --machine=CONTAINER
                      Operate on local container
  -t --type=TYPE      List units of a particular type
     --state=STATE    List units with particular LOAD or SUB or ACTIVE state
  -p --property=NAME  Show only properties by this name
  -a --all            Show all loaded units/properties, including dead/empty
                      ones. To list all units installed on the system, use
                      the 'list-unit-files' command instead.
  -l --full           Don't ellipsize unit names on output
  -r --recursive      Show unit list of host and local containers
     --reverse        Show reverse dependencies with 'list-dependencies'
     --job-mode=MODE  Specify how to deal with already queued jobs, when
                      queueing a new job
     --show-types     When showing sockets, explicitly show their type
  -i --ignore-inhibitors
                      When shutting down or sleeping, ignore inhibitors
     --kill-who=WHO   Who to send signal to
  -s --signal=SIGNAL  Which signal to send
     --now            Start or stop unit in addition to enabling or disabling it
  -q --quiet          Suppress output
     --no-block       Do not wait until operation finished
     --no-wall        Don't send wall message before halt/power-off/reboot
     --no-reload      Don't reload daemon after en-/dis-abling unit files
     --no-legend      Do not print a legend (column headers and hints)
     --no-pager       Do not pipe output into a pager
     --no-ask-password
                      Do not ask for system passwords
     --global         Enable/disable unit files globally
     --runtime        Enable unit files only temporarily until next reboot
  -f --force          When enabling unit files, override existing symlinks
                      When shutting down, execute action immediately
     --preset-mode=   Apply only enable, only disable, or all presets
     --root=PATH      Enable unit files in the specified root directory
  -n --lines=INTEGER  Number of journal entries to show
  -o --output=STRING  Change journal output mode (short, short-iso,
                              short-precise, short-monotonic, verbose,
                              export, json, json-pretty, json-sse, cat)
     --plain          Print unit dependencies as a list instead of a tree

Unit Commands:
  list-units [PATTERN...]         List loaded units
  list-sockets [PATTERN...]       List loaded sockets ordered by address
  list-timers [PATTERN...]        List loaded timers ordered by next elapse
  start NAME...                   Start (activate) one or more units
  stop NAME...                    Stop (deactivate) one or more units
  reload NAME...                  Reload one or more units
  restart NAME...                 Start or restart one or more units
  try-restart NAME...             Restart one or more units if active
  reload-or-restart NAME...       Reload one or more units if possible,
                                  otherwise start or restart
  reload-or-try-restart NAME...   Reload one or more units if possible,
                                  otherwise restart if active
  isolate NAME                    Start one unit and stop all others
  kill NAME...                    Send signal to processes of a unit
  is-active PATTERN...            Check whether units are active
  is-failed PATTERN...            Check whether units are failed
  status [PATTERN...|PID...]      Show runtime status of one or more units
  show [PATTERN...|JOB...]        Show properties of one or more
                                  units/jobs or the manager
  cat PATTERN...                  Show files and drop-ins of one or more units
  set-property NAME ASSIGNMENT... Sets one or more properties of a unit
  help PATTERN...|PID...          Show manual for one or more units
  reset-failed [PATTERN...]       Reset failed state for all, one, or more
                                  units
  list-dependencies [NAME]        Recursively show units which are required
                                  or wanted by this unit or by which this
                                  unit is required or wanted

Unit File Commands:
  list-unit-files [PATTERN...]    List installed unit files
  enable NAME...                  Enable one or more unit files
  disable NAME...                 Disable one or more unit files
  reenable NAME...                Reenable one or more unit files
  preset NAME...                  Enable/disable one or more unit files
                                  based on preset configuration
  preset-all                      Enable/disable all unit files based on
                                  preset configuration
  is-enabled NAME...              Check whether unit files are enabled
  mask NAME...                    Mask one or more units
  unmask NAME...                  Unmask one or more units
  link PATH...                    Link one or more units files into
                                  the search path
  add-wants TARGET NAME...        Add 'Wants' dependency for the target
                                  on specified one or more units
  add-requires TARGET NAME...     Add 'Requires' dependency for the target
                                  on specified one or more units
  edit NAME...                    Edit one or more unit files
  get-default                     Get the name of the default target
  set-default NAME                Set the default target

Machine Commands:
  list-machines [PATTERN...]      List local containers and host

Job Commands:
  list-jobs [PATTERN...]          List jobs
  cancel [JOB...]                 Cancel all, one, or more jobs

Snapshot Commands:
  snapshot [NAME]                 Create a snapshot
  delete NAME...                  Remove one or more snapshots

Environment Commands:
  show-environment                Dump environment
  set-environment NAME=VALUE...   Set one or more environment variables
  unset-environment NAME...       Unset one or more environment variables
  import-environment [NAME...]    Import all or some environment variables

Manager Lifecycle Commands:
  daemon-reload                   Reload systemd manager configuration
  daemon-reexec                   Reexecute systemd manager

System Commands:
  is-system-running               Check whether system is fully running
  default                         Enter system default mode
  rescue                          Enter system rescue mode
  emergency                       Enter system emergency mode
  halt                            Shut down and halt the system
  poweroff                        Shut down and power-off the system
  reboot [ARG]                    Shut down and reboot the system
  kexec                           Shut down and reboot the system with kexec
  exit                            Request user instance exit
  switch-root ROOT [INIT]         Change to a different root file system
  suspend                         Suspend the system
  hibernate                       Hibernate the system
  hybrid-sleep                    Hibernate and suspend the system

一、Systemd简介

Systemd是由红帽公司的一名叫做Lennart Poettering的员工开发，systemd是Linux系统中最新的初始化系统（init）,它主要的设计目的是克服Sys V 固有的缺点，提高系统的启动速度。

systemd和upstart是竞争对手，ubantu上使用的是upstart的启动方式，centos7上使用systemd替换了Sys V，Systemd目录是要取代Unix时代依赖一直在使用的init系统，兼容SysV和LSB的启动脚本，

而且能够在进程启动中更有效地引导加载服务。
system：系统启动和服务器守护进程管理器，负责在系统启动或运行时，激活系统资源，服务器进程和其他进程，根据管理，字母d是守护进程（daemon）的缩写，systemd这个名字的含义就是它要守护整个系统。

二、Systemd新特性

系统引导时实现服务并行启动
按需启动守护进程
自动化的服务依赖关系管理
同时采用socket式与D-Bus总线式激活服务
系统状态快照和恢复
利用Linux的cgroups监视进程
维护挂载点和自动挂载点
各服务间基于依赖关系进行精密控制

三、Systemd核心概念

Unit
表示不同类型的sytemd对象，通过配置文件进行标识和配置，文件中主要包含了系统服务，监听socket、保存的系统快照以及其他与init相关的信息
配置文件:
/usr/lib/systemd/system：每个服务最主要的启动脚本设置，类似于之前的/etc/initd.d
/run/system/system：系统执行过程中所产生的服务脚本，比上面的目录优先运行
/etc/system/system：管理员建立的执行脚本，类似于/etc/rc.d/rcN.d/Sxx类的功能，比上面目录优先运行，在三者之中，此目录优先级最高

四、Unit类型

systemctl -t help ：查看unit类型
service unit：文件扩展名为.service，用于定义系统服务
target unit：文件扩展名为.target，用于模拟实现“运行级别”
device unit: .device,用于定义内核识别的设备
mount unit ：.mount，定义文件系统挂载点
socket unit ：.socket,用于标识进程间通信用的socket文件，也可以在系统启动时，延迟启动服务，实现按需启动
snapshot unit：.snapshot，关系系统快照
swap unit：.swap，用于表示swap设备
automount unit：.automount，文件系统的自动挂载点如：/misc目录
path unit：.path，用于定义文件系统中的一个文件或目录使用，常用于当文件系统变化时，延迟激活服务，如spool目录
time：.timer由systemd管理的计时器

注：使用systemctl控制单元时，通常需要使用单元文件的全名，包括扩展名，但是有些单元可以在systemctl中使用简写方式，如果无扩展名，systemctl默认把扩展名当做.service。例如netcfg和netcfg.service是等同的挂载点会自动转化为相应的.mount单元，例如/home等价于home.mount设备会自动转化为相应的.device单元，所以/dev/sd2等价于dev-sda2.device

五、关键特性

基于socket的激活机制：socket与服务进程分离
基于D-Bus的激活机制
基于device的激活机制
基于path的激活机制
系统快照：保存各unit的当前状态信息于持久存储设备中想后兼容sysv init脚本

六、不兼容

systemctl命令固定不变，不可扩展
非由systemd启动的服务，systemctl无语与之通信和控制，如：使用之前sys v风格管理的进程就无法收systemd控制

七、Systemd基本工具

监视和控制systemd的主要命令是systemctl。该命令可用于查看系统状态和管理系统及服务。

管理服务

　　命令：systemctl command name.service

　　启动：service name start –>systemctl start name.service

　　停止：service name stop –>systemctl stop name.service

　　重启：service name restart–>systemctl restart name.service

　　状态：service name status–>systemctl status name.service

条件式重启(已启动才重启，否则不做任何操作)
systemctl try-restart name.service
重载或重启服务(先加载，然后再启动)
systemctl reload-or-try-restart name.service
禁止自动和手动启动
systemctl mask name.service
执行此条命令实则创建了一个链接 ln -s ‘/dev/null’ ‘/etc/systemd/system/sshd.service’
取消禁止
systemctl unmask name.service
删除此前创建的链接
服务查看(查看某服务当前激活与否的状态)
systemctl is-active name.service
如果启动会显示active，否则会显示unknown
查看所有已经激活的服务
systemctl list-units –t|–type service

[root@hadoop01 hadoop]# systemctl –helpsystemctl [OPTIONS…] {COMMAND} …
Query or send control commands to the systemd manager.
-h –help Show this help –version Show package version –system Connect to system manager -H –host=[USER@]HOST Operate on remote host -M –machine=CONTAINER Operate on local container -t –type=TYPE List units of a particular type –state=STATE List units with particular LOAD or SUB or ACTIVE state -p –property=NAME Show only properties by this name -a –all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the ‘list-unit-files’ command instead. -l –full Don’t ellipsize unit names on output -r –recursive Show unit list of host and local containers –reverse Show reverse dependencies with ‘list-dependencies’ –job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job –show-types When showing sockets, explicitly show their type -i –ignore-inhibitors When shutting down or sleeping, ignore inhibitors –kill-who=WHO Who to send signal to -s –signal=SIGNAL Which signal to send –now Start or stop unit in addition to enabling or disabling it -q –quiet Suppress output –no-block Do not wait until operation finished –no-wall Don’t send wall message before halt/power-off/reboot –no-reload Don’t reload daemon after en-/dis-abling unit files –no-legend Do not print a legend (column headers and hints) –no-pager Do not pipe output into a pager –no-ask-password Do not ask for system passwords –global Enable/disable unit files globally –runtime Enable unit files only temporarily until next reboot -f –force When enabling unit files, override existing symlinks When shutting down, execute action immediately –preset-mode= Apply only enable, only disable, or all presets –root=PATH Enable unit files in the specified root directory -n –lines=INTEGER Number of journal entries to show -o –output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) –plain Print unit dependencies as a list instead of a tree
Unit Commands: list-units [PATTERN…] List loaded units list-sockets [PATTERN…] List loaded sockets ordered by address list-timers [PATTERN…] List loaded timers ordered by next elapse start NAME… Start (activate) one or more units stop NAME… Stop (deactivate) one or more units reload NAME… Reload one or more units restart NAME… Start or restart one or more units try-restart NAME… Restart one or more units if active reload-or-restart NAME… Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME… Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME… Send signal to processes of a unit is-active PATTERN… Check whether units are active is-failed PATTERN… Check whether units are failed status [PATTERN…|PID…] Show runtime status of one or more units show [PATTERN…|JOB…] Show properties of one or more units/jobs or the manager cat PATTERN… Show files and drop-ins of one or more units set-property NAME ASSIGNMENT… Sets one or more properties of a unit help PATTERN…|PID… Show manual for one or more units reset-failed [PATTERN…] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted
systemctl [OPTIONS…] {COMMAND} …
Query or send control commands to the systemd manager.
-h –help Show this help –version Show package versionsystemctl [OPTIONS…] {COMMAND} …
systemctl [OPTIONS…] {COMMAND} …
Query or send control commands to the systemd manager.
-h –help Show this help –version Show package version –system Connect to system manager -H –host=[USER@]HOST Operate on remote host -M –machine=CONTAINER Operate on local container -t –type=TYPE List units of a particular type –state=STATE List units with particular LOAD or SUB or ACTIVE state -p –property=NAME Show only properties by this name -a –all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the ‘list-unit-files’ command instead. -l –full Don’t ellipsize unit names on output -r –recursive Show unit list of host and local containers –reverse Show reverse dependencies with ‘list-dependencies’ –job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job –show-types When showing sockets, explicitly show their type -i –ignore-inhibitors When shutting down or sleeping, ignore inhibitors –kill-who=WHO Who to send signal to -s –signal=SIGNAL Which signal to send –now Start or stop unit in addition to enabling or disabling it -q –quiet Suppress output –no-block Do not wait until operation finished –no-wall Don’t send wall message before halt/power-off/reboot –no-reload Don’t reload daemon after en-/dis-abling unit files –no-legend Do not print a legend (column headers and hints) –no-pager Do not pipe output into a pager –no-ask-password Do not ask for system passwords –global Enable/disable unit files globally –runtime Enable unit files only temporarily until next reboot -f –force When enabling unit files, override existing symlinks When shutting down, execute action immediately –preset-mode= Apply only enable, only disable, or all presets –root=PATH Enable unit files in the specified root directory -n –lines=INTEGER Number of journal entries to show -o –output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) –plain Print unit dependencies as a list instead of a tree
Unit Commands: list-units [PATTERN…] List loaded units list-sockets [PATTERN…] List loaded sockets ordered by address list-timers [PATTERN…] List loaded timers ordered by next elapse start NAME… Start (activate) one or more units stop NAME… Stop (deactivate) one or more units reload NAME… Reload one or more units restart NAME… Start or restart one or more units try-restart NAME… Restart one or more units if active reload-or-restart NAME… Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME… Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME… Send signal to processes of a unit is-active PATTERN… Check whether units are active is-failed PATTERN… Check whether units are failed status [PATTERN…|PID…] Show runtime status of one or more units show [PATTERN…|JOB…] Show properties of one or more units/jobs or the manager cat PATTERN… Show files and drop-ins of one or more units set-property NAME ASSIGNMENT… Sets one or more properties of a unit help PATTERN…|PID… Show manual for one or more units reset-failed [PATTERN…] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted
Unit File Commands: list-unit-files [PATTERN…] List installed unit files enable NAME… Enable one or more unit files disable NAME… Disable one or more unit files reenable NAME… Reenable one or more unit files preset NAME… Enable/disable one or more unit files based on preset configuration preset-all Enable/disable all unit files based on preset configuration is-enabled NAME… Check whether unit files are enabled mask NAME… Mask one or more units unmask NAME… Unmask one or more units link PATH… Link one or more units files into the search path add-wants TARGET NAME… Add ‘Wants’ dependency for the target on specified one or more units add-requires TARGET NAME… Add ‘Requires’ dependency for the target on specified one or more units edit NAME… Edit one or more unit files get-default Get the name of the default target set-default NAME Set the default target
Machine Commands: list-machines [PATTERN…] List local containers and host
Job Commands: list-jobs [PATTERN…] List jobs cancel [JOB…] Cancel all, one, or more jobs
Snapshot Commands: snapshot [NAME] Create a snapshot delete NAME… Remove one or more snapshots
Environment Commands: show-environment Dump environment set-environment NAME=VALUE… Set one or more environment variables unset-environment NAME… Unset one or more environment variables import-environment [NAME…] Import all or some environment variables
Manager Lifecycle Commands: daemon-reload Reload systemd manager configuration daemon-reexec Reexecute systemd manager
System Commands: is-system-running Check whether system is fully running default Enter system default mode rescue Enter system rescue mode emergency Enter system emergency mode halt Shut down and halt the system poweroff Shut down and power-off the system reboot [ARG] Shut down and reboot the system kexec Shut down and reboot the system with kexec exit Request user instance exit switch-root ROOT [INIT] Change to a different root file system suspend Suspend the system hibernate Hibernate the system hybrid-sleep Hibernate and suspend the system

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