This article brings you relevant knowledge about Linux. It mainly introduces the relationship between systemctl and service and chkconfig commands, as well as the differences. Let’s take a look at them together. I hope it will be helpful to everyone.

The relationship between systemctl and service and chkconfig commands

systemctl command: It is a systemd tool, mainly responsible for controlling the systemd system and service manager.
service command: You can start, stop, restart, and shut down system services, and you can also display the current status of all system services.
chkconfig command: It is a command line tool for managing system services (service). The so-called system service (service) is a program that starts when the system starts and closes when the system shuts down.

The systemctl command is a system service manager command, which actually combines the two commands service and chkconfig.

systemctl is the main tool among the service management tools of RHEL 7. It integrates the functions of the previous service and chkconfig. You can use it to enable/disable services permanently or only for the current session.

So the systemctl command is a collection and replacement of the service command and the chkconfig command.

For example: using service to start the service actually calls the systemctl command.

[root@localhost ~]# service httpd start
Redirecting to /bin/systemctl start  httpd.service

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Usage of systemctl command

Systemctl command introduction:

Systemctl is a systemd tool, mainly responsible for controlling the systemd system and service manager.

Systemd is a collection of system management daemons, tools and libraries used to replace the System V initial process. The function of Systemd is to centrally manage and configure UNIX-like systems.

Systemd is system daemon, which is an init software under Linux.

Common usage of Systemctl command:

(1) List all available units:

[root@localhost ~]# systemctl list-unit-files 
UNIT FILE                                  STATE   
proc-sys-fs-binfmt_misc.automount          static  
dev-hugepages.mount                        static  
dev-mqueue.mount                           static  
proc-fs-nfsd.mount                         static  
proc-sys-fs-binfmt_misc.mount              static  
sys-fs-fuse-connections.mount              static  
sys-kernel-config.mount                    static  
sys-kernel-debug.mount                     static  
tmp.mount                                  disabled
var-lib-nfs-rpc_pipefs.mount               static  
brandbot.path                              disabled
cups.path                                  enabled

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(2) List all available units:

[root@localhost ~]# systemctl list-units
  UNIT                      LOAD      ACTIVE SUB       DESCRIPTION
  proc-sys-fs-binfmt_misc.automount loaded    active waiting   Arbitrary 
  sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda
  sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda
  sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda
  sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:1-2:0:1:0-block-sdb
  sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:1-2:0:1:0-block-sdb
  sys-devices-pci0000:00-0000:00:11.0-0000:02:01.0-net-ens33.device loade
  sys-devices-pci0000:00-0000:00:11.0-0000:02:02.0-sound-card0.device lo
 ..............

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(3) List all failed units:

[root@localhost ~]# systemctl --failed 
  UNIT                LOAD   ACTIVE SUB    DESCRIPTION
● network.service     loaded failed failed LSB: Bring up/down networking
● teamd@team0.service loaded failed failed Team Daemon for device team0

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB
SUB    = The low-level unit activation state, values depend on unit type.

2 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use &#39;systemctl list-unit-files&#39;.

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(4) Check whether a unit is started:

[root@localhost ~]# systemctl is-enabled httpd.service 
enabled

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(5) Check the running status of a service:

[root@localhost ~]# systemctl status httpd.service     
● httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
   Active: active (running) since 日 2018-10-14 18:21:46 CST; 1 day 2h ago
     Docs: man:httpd(8)
           man:apachectl(8)
 Main PID: 19020 (httpd)
   Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"
   CGroup: /system.slice/httpd.service
           ├─19020 /usr/sbin/httpd -DFOREGROUND
           ├─27310 /usr/sbin/httpd -DFOREGROUND
           ├─27311 /usr/sbin/httpd -DFOREGROUND
           ├─27312 /usr/sbin/httpd -DFOREGROUND
           ├─27313 /usr/sbin/httpd -DFOREGROUND
           └─27314 /usr/sbin/httpd -DFOREGROUND

10月 14 18:21:46 localhost systemd[1]: Starting The Apache HTTP Serv....
10月 14 18:21:46 localhost httpd[19020]: AH00558: httpd: Could not r...e

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(6) List all services:

[root@localhost ~]# systemctl list-unit-files --type=service
UNIT FILE                                  STATE   
abrt-ccpp.service                          enabled 
abrt-oops.service                          enabled 
abrt-pstoreoops.service                    disabled
abrt-xorg.service                          enabled 
abrtd.service                              enabled 
accounts-daemon.service                    enabled 
alsa-restore.service                       static  
alsa-state.service                         static  
alsa-store.service                         static  
arp-ethers.service                         disabled
atd.service                                disabled
auditd.service                             enabled 
auth-rpcgss-module.service                 static

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(7) Start, stop, restart services, etc.:

[root@localhost ~]# systemctl restart httpd.service
# systemctl restart httpd.service
# systemctl stop httpd.service
# systemctl reload httpd.service
# systemctl status httpd.service

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(8) Check whether the service is activated and configured Start up:

[root@localhost ~]# systemctl is-active httpd
active
[root@localhost ~]# systemctl disable httpd
Removed symlink /etc/systemd/system/multi-user.target.wants/httpd.service.
[root@localhost ~]# systemctl enable httpd 
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.

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(9) Use the systemctl command to kill the service:

[root@localhost ~]# systemctl kill httpd

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(10) List the various services, mounts, devices, etc. of the system:

[root@localhost ~]# systemctl list-unit-files --type 
automount  device     path       snapshot   swap       timer
busname    mount      service    socket     target

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(11) Obtain the system default startup level and set the default startup level:

[root@localhost ~]# systemctl get-default 
graphical.target
[root@localhost ~]# systemctl set-default multi-user.target

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(12) Start the running level:

systemctl isolate multiuser.target

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(13) Restart, stop, suspend, hibernate the system, etc.:

# systemctl reboot
# systemctl halt
# systemctl suspend
# systemctl hibernate
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Service命令用法

service命令可以启动、停止、重新启动和关闭系统服务，还可以显示所有系统服务的当前状态。

service命令的作用是去/etc/init.d目录下寻找相应的服务，进行开启和关闭等操作。

使用示例：

开启关闭一个服务：service httpd start/stop

[root@localhost ~]# service httpd start
Redirecting to /bin/systemctl start  httpd.service

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查看系统服务的状态：service –status-all

[root@localhost ~]# service --status-all
未加载 netconsole 模块
已配置设备：
lo ens33 ens33.old team0 team0-port1 team0-port1.old team0-port2 team0-port2.old team0.old
当前活跃设备：
lo ens33 virbr0 ens38 ens39 team0
● rhnsd.service - LSB: Starts the Spacewalk Daemon
   Loaded: loaded (/etc/rc.d/init.d/rhnsd; bad; vendor preset: disabled)
   Active: active (running) since 五 2018-10-12 14:53:19 CST; 3 days ago
     Docs: man:systemd-sysv-generator(8)
 Main PID: 1380 (rhnsd)
   CGroup: /system.slice/rhnsd.service
           └─1380 rhnsd

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chkconfig命令用法

chkconfig是管理系统服务(service)的命令行工具。所谓系统服务(service)，就是随系统启动而启动，随系统关闭而关闭的程序。

chkconfig可以更新(启动或停止)和查询系统服务(service)运行级信息。更简单一点，chkconfig是一个用于维护/etc/rc[0-6].d目录的命令行工具。

chkconfig常见用法：

[root@localhost ~]# chkconfig  --help
chkconfig 版本 1.7.2 - 版权 (C) 1997-2000 红帽公司
在 GNU 公共许可条款下，本软件可以自由重发行。

用法：   chkconfig [--list] [--type <类型>] [名称]
         chkconfig --add <名称>
         chkconfig --del <名称>
         chkconfig --override <名称>
         chkconfig [--level <级别>] [--type <类型>] <名称> <on|off|reset|resetpriorities>

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（一）设置service开机是否启动：

chkconfig name on/off/reset

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on、off、reset用于改变service的启动信息。
on表示开启，off表示关闭，reset表示重置。
默认情况下，on和off开关只对运行级2，3，4，5有效，reset可以对所有运行级有效。

[root@localhost ~]# chkconfig httpd on
注意：正在将请求转发到“systemctl enable httpd.service”。

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在Redhat7上，运行chkconfig命令，都会被转到systemcle命令上。

（2）设置service运行级别：

chkconfig --level levels

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该命令可以用来指定服务的运行级别，即指定运行级别2,3,4,5等。

等级0表示：表示关机
等级1表示：单用户模式
等级2表示：无网络连接的多用户命令行模式
等级3表示：有网络连接的多用户命令行模式
等级4表示：不可用
等级5表示：带图形界面的多用户模式
等级6表示：重新启动

例如：

[root@localhost ~]# chkconfig --level 5 httpd on
注意：正在将请求转发到“systemctl enable httpd.service”

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（三）列出service启动信息：

# chkconfig --list [name]

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如果不指定name，会列出所有services的信息。

每个service每个运行级别都会有一个启动和停止脚本；当切换运行级别时，init不会重启已经启动的service，也不会重新停止已经停止的service。

例如：

[root@localhost ~]# chkconfig --list

注意：该输出结果只显示 SysV 服务，并不包含原生 systemd 服务。SysV 配置数据可能被原生 systemd 配置覆盖。 
      如果您想列出 systemd 服务,请执行 &#39;systemctl list-unit-files&#39;。
      欲查看对特定 target 启用的服务请执行
      &#39;systemctl list-dependencies [target]&#39;。

netconsole      0:关    1:关    2:关    3:关    4:关    5:关    6:关
network         0:关    1:关    2:开    3:开    4:开    5:开    6:关
rhnsd           0:关    1:关    2:开    3:开    4:开    5:开    6:关

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总结：service命令的功能基本都被systemct取代。直接使用systemctl命令即可。

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