linux命令学习之：systemctl

2022-07-14 20:20:29

　　systemctl命令是系统服务管理器指令，主要负责控制systemd系统和服务管理器，它实际上将 service 和 chkconfig 这两个命令组合到一起。

　　CentOS 7.x开始，CentOS开始使用systemd服务来代替daemon，原来管理系统启动和管理系统服务的相关命令全部由systemctl命令来代替。

　　Systemd是一个系统管理守护进程、工具和库的集合，用于取代System V初始进程。Systemd的功能是用于集中管理和配置类UNIX系统。

　　在Linux生态系统中，Systemd被部署到了大多数的标准Linux发行版中，只有为数不多的几个发行版尚未部署。Systemd通常是所有其它守护进程的父进程，但并非全是如此。

1、原来的 service 命令与 systemctl 命令对比

daemon命令	systemctl命令	说明
service [服务] start	systemctl start [unit type]	启动服务
service [服务] stop	systemctl stop [unit type]	停止服务
service [服务] restart	systemctl restart [unit type]	重启服务

此外还是二个systemctl参数没有与service命令参数对应

status：参数来查看服务运行情况
reload：重新加载服务，加载更新后的配置文件（并不是所有服务都支持这个参数，比如network.service）

　　示例：

#启动网络服务

systemctl start network.service

#停止网络服务

systemctl stop network.service

#重启网络服务

systemctl restart network.service

#查看网络服务状态

systemctl status network.serivce

2、原来的chkconfig 命令与 systemctl 命令对比

daemon命令	systemctl命令	说明
chkconfig [服务] on	systemctl enable [unit type]	设置服务开机启动
chkconfig [服务] off	systemctl disable [unit type]	设备服务禁止开机启动

　　示例：

#停止cup电源管理服务

systemctl stop cups.service

#禁止cups服务开机启动

systemctl disable cups.service

#查看cups服务状态

systemctl status cups.service

#重新设置cups服务开机启动

systemctl enable cups.service

3、查看系统上上所有的服务

　　命令格式：systemctl [command] [–type=TYPE] [–all]

　　参数详解：

　　command - list-units：依据unit列出所有启动的unit。加上 –all 才会列出没启动的unit; - list-unit-files:依据/usr/lib/systemd/system/ 内的启动文件，列出启动文件列表

–type=TYPE - 为unit type, 主要有service, socket, target

　　应用举例：

systemctl命令	说明
systemctl	列出所有的系统服务
systemctl list-units	列出所有启动unit
systemctl list-unit-files	列出所有启动文件
systemctl list-units –type=service –all	列出所有service类型的unit
systemctl list-units –type=service –all grep cpu	列出 cpu电源管理机制的服务
systemctl list-units –type=target –all	列出所有target

4、systemctl特殊的用法

systemctl命令	说明
systemctl is-active [unit type]	查看服务是否运行
systemctl is-enable [unit type]	查看服务是否设置为开机启动
systemctl mask [unit type]	注销指定服务
systemctl unmask [unit type]	取消注销指定服务

　　应用举例：

#查看网络服务是否启动

systemctl is-active network.service

#检查网络服务是否设置为开机启动

systemctl is-enable network.service

#停止cups服务

systemctl stop cups.service

#注销cups服务

systemctl mask cups.service

#查看cups服务状态

systemctl status cups.service

#取消注销cups服务

systemctl unmask cups.service

5、常用示例：

Systemctl基础、体验

1. 检查系统中是否安装有systemctl并确定当前安装的版本

[root@CTU1000094955 ~]# systemctl --version

systemd

+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN

　　上例中很清楚地表明，我们安装了219版本的systemctl。

2. 检查systemd和systemctl的二进制文件和库文件的安装位置

[root@CTU1000094955 ~]# whereis systemd

systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd..gz

[root@CTU1000094955 ~]# whereis systemctl

systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl..gz

3. 检查systemd是否运行

[root@CTU1000094955 ~]# ps -eaf | grep [s]ystemd

root                   : ?        :: /usr/lib/systemd/systemd --switched-root --system --deserialize

root                 : ?        :: /usr/lib/systemd/systemd-journald

root                 : ?        :: /usr/lib/systemd/systemd-udevd

dbus                 : ?        :: /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation

root                 : ?        :: /usr/lib/systemd/systemd-logind

　　注意：systemd是作为父进程（PID=1）运行的。在上面带（-e）参数的ps命令输出中，选择所有进程，（-a）选择除会话前导外的所有进程，并使用（-f）参数输出完整格式列表（即 -eaf）。

　　也请注意上例中后随的方括号和例子中剩余部分。方括号表达式是grep的字符类表达式的一部分。

4. 分析systemd启动进程

[root@CTU1000094955 ~]# systemd-analyze

Startup finished in 743ms (kernel) + .959s (initrd) + .696s (userspace) = .399s

5. 分析启动时各个进程花费的时间

[root@CTU1000094955 ~]# systemd-analyze blame
.859s dev-xvda1.device

          .670s NetworkManager-wait-online.service

          .610s plymouth-quit-wait.service

          .757s systemd-udev-settle.service

          .078s kdump.service

          .257s mysql.service

          .451s libvirtd.service

          .228s postfix.service

           751ms uvp-monitor.service

           675ms spesserviced.service

           675ms messageserviced.service

           660ms tuned.service

           586ms network.service

           525ms accounts-daemon.service

           467ms NetworkManager.service

           457ms systemd-udevd.service

           416ms abrt-ccpp.service

           397ms firewalld.service

           365ms ModemManager.service

6. 分析启动时的关键链

[root@CTU1000094955 ~]# systemd-analyze critical-chain

The time after the unit is active or started is printed after the "@" character.

The time the unit takes to start is printed after the "+" character.

graphical.target @.682s

?..multi-user.target @.682s

  ?..getty.target @.682s

    ?..serial-getty@hvc0.service @.681s

      ?..systemd-user-sessions.service @.929s +18ms

        ?..remote-fs.target @.921s

          ?..remote-fs-pre.target @.921s

            ?..iscsi-shutdown.service @.907s +12ms

              ?..network.target @.900s

                ?..network.service @.311s +586ms

                  ?..NetworkManager.service @.166s +467ms

                    ?..basic.target @.903s

                      ?..sockets.target @.903s

                        ?..rpcbind.socket @.903s

                          ?..sysinit.target @.895s

                            ?..systemd-update-utmp.service @.877s +16ms

                              ?..auditd.service @.738s +135ms

                                ?..systemd-tmpfiles-setup.service @.661s +73ms

                                  ?..rhel-import-state.service @.526s +134ms

                                    ?..local-fs.target @.525s

                                      ?..run-user-.mount @.041s

                                        ?..local-fs-pre.target @.615s

                                          ?..systemd-tmpfiles-setup-dev.service @

                                            ?..kmod-static-nodes.service @.473s

                                              ?..systemd-journald.socket

                                                ?..-.slice

　　重要：Systemctl接受服务（.service），挂载点（.mount），套接口（.socket）和设备（.device）作为单元。

7. 列出所有可用单元

[root@CTU1000094955 ~]# 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

systemd-ask-password-console.path           static

8. 列出所有运行中单元

[root@CTU1000094955 ~]# systemctl list-units

  UNIT                                                                               LOAD   ACTIVE SUB       DESCRIPTION

  proc-sys-fs-binfmt_misc.automount                                                  loaded active waiting   Arbitrary Executable File Formats File System Automount Point

  sys-devices-pci0000:-::01.1-ata2-host1-target1::-:::-block-sr0.device loaded active plugged   QEMU_DVD-ROM

  sys-devices-platform-serial8250-tty-ttyS2.device                                   loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS2

  sys-devices-platform-serial8250-tty-ttyS3.device                                   loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS3

  sys-devices-pnp0-:-tty-ttyS0.device                                            loaded active plugged   /sys/devices/pnp0/:/tty/ttyS0

  sys-devices-pnp0-:-tty-ttyS1.device                                            loaded active plugged   /sys/devices/pnp0/:/tty/ttyS1

  sys-devices-vbd\x2d51712-block-xvda-xvda1.device                                   loaded active plugged   /sys/devices/vbd-/block/xvda/xvda1

  sys-devices-vbd\x2d51712-block-xvda-xvda2.device                                   loaded active plugged   /sys/devices/vbd-/block/xvda/xvda2

  sys-devices-vbd\x2d51712-block-xvda.device                                         loaded active plugged   /sys/devices/vbd-/block/xvda

  sys-devices-vbd\x2d51776-block-xvde.device                                         loaded active plugged   LVM PV I2rhCm-www3-J79i-r3ei-1XCb-a1qS-3OWSg9 on /dev/xvde

  sys-devices-vif\x2d0-net-eth0.device                                               loaded active plugged   /sys/devices/vif-/net/eth0

9. 列出所有失败单元

[root@CTU1000094955 ~]# systemctl --failed

  UNIT              LOAD   ACTIVE SUB    DESCRIPTION

?.bluetooth.service loaded failed failed Bluetooth service

?.rc-local.service  loaded failed failed /etc/rc.d/rc.local Compatibility

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.

 loaded units listed. Pass --all to see loaded but inactive units, too.

To show all installed unit files use 'systemctl list-unit-files'.

10. 检查某个单元（如 cron.service）是否启用

[root@CTU1000094955 ~]# systemctl is-enabled firewalld.service
disabled

11. 检查某个单元或服务是否运行

[root@CTU1000094955 ~]# systemctl status firewalld.service

?.firewalld.service - firewalld - dynamic firewall daemon

   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)

   Active: active (running) since Sat -- :: CST; 1h 29min ago

 Main PID:  (firewalld)

   CGroup: /system.slice/firewalld.service

           ?.. /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

使用Systemctl控制并管理服务

12. 列出所有服务（包括启用的和禁用的）

[root@CTU1000094955 ~]# systemctl list-unit-files --type=service

UNIT FILE                                   STATE

abrt-ccpp.service                           enabled

abrt-oops.service                           enabled

abrt-pstoreoops.service                     disabled

abrt-vmcore.service                         enabled

abrt-xorg.service                           enabled

abrtd.service                               enabled

accounts-daemon.service                     enabled

alsa-restore.service                        static

alsa-state.service                          static

alsa-store.service                          static

anaconda-direct.service                     static

anaconda-nm-config.service                  static

anaconda-noshell.service                    static

anaconda-shell@.service                     static

13. Linux中如何启动、重启、停止、重载服务以及检查服务（如 firewalld.service）状态

[root@CTU1000094955 ~]# systemctl start httpd.service

Failed to start httpd.service: Unit httpd.service failed to load: No such file or directory.

[root@CTU1000094955 ~]# systemctl start firewalld.service

[root@CTU1000094955 ~]# systemctl restart firewalld.service

[root@CTU1000094955 ~]# systemctl stop firewalld.service

[root@CTU1000094955 ~]# systemctl reload firewalld.service

Job for firewalld.service invalid.

[root@CTU1000094955 ~]# systemctl status firewalld.service
?.firewalld.service - firewalld - dynamic firewall daemon

   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)

   Active: inactive (dead)

Nov  :: CTU1000094955 systemd[]: Stopped firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Stopping firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Stopping firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Stopped firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Unit firewalld.service cannot be reloaded because it is inactive.

[root@CTU1000094955 ~]# systemctl restart firewalld.service

[root@CTU1000094955 ~]# systemctl reload firewalld.service

[root@CTU1000094955 ~]# systemctl status firewalld.service
?.firewalld.service - firewalld - dynamic firewall daemon

   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)

   Active: active (running) since Sat -- :: CST; 8s ago

  Process:  ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=/SUCCESS)

 Main PID:  (firewalld)

   CGroup: /system.slice/firewalld.service

           ?.. /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Reloaded firewalld - dynamic firewall daemon.

　　注意：当我们使用systemctl的start，restart，stop和reload命令时，我们不会从终端获取到任何输出内容，只有status命令可以打印输出。

14. 如何激活服务并在启动时启用或禁用服务（即系统启动时自动启动服务）

[root@CTU1000094955 ~]# systemctl is-active firewalld.service

active

[root@CTU1000094955 ~]# systemctl enable firewalld.service

Created symlink from /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service to /usr/lib/systemd/system/firewalld.service.

Created symlink from /etc/systemd/system/basic.target.wants/firewalld.service to /usr/lib/systemd/system/firewalld.service.

[root@CTU1000094955 ~]# systemctl list-unit-files |grep firewall

firewalld.service                           enabled

[root@CTU1000094955 ~]# systemctl status firewalld.service

?.firewalld.service - firewalld - dynamic firewall daemon

   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)

   Active: active (running) since Sat -- :: CST; 4min 6s ago

 Main PID:  (firewalld)

   CGroup: /system.slice/firewalld.service

           ?.. /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Reloaded firewalld - dynamic firewall daemon.

[root@CTU1000094955 ~]# systemctl disable firewalld.service

Removed symlink /etc/systemd/system/basic.target.wants/firewalld.service.

Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.

[root@CTU1000094955 ~]# systemctl list-unit-files |grep firewall

firewalld.service                           disabled

15. 如何屏蔽（让它不能启动）或显示服务（如 httpd.service）

[root@CTU1000094955 ~]# systemctl mask firewalld.service

Created symlink from /etc/systemd/system/firewalld.service to /dev/null.

[root@CTU1000094955 ~]# systemctl unmask firewalld.service

Removed symlink /etc/systemd/system/firewalld.service.

16. 使用systemctl命令杀死服务

[root@CTU1000094955 ~]# systemctl kill httpd

Failed to kill unit httpd.service: Unit httpd.service is not loaded.

[root@CTU1000094955 ~]# systemctl kill firewalld.service

[root@CTU1000094955 ~]# systemctl status firewalld.service

?.firewalld.service - firewalld - dynamic firewall daemon

   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)

   Active: inactive (dead) since Sat -- :: CST; 7s ago

 Main PID:  (code=exited, status=/SUCCESS)

Nov  :: CTU1000094955 systemd[]: Starting firewalld - dynamic firewall daemon...

Nov  :: CTU1000094955 systemd[]: Started firewalld - dynamic firewall daemon.

Nov  :: CTU1000094955 systemd[]: Reloaded firewalld - dynamic firewall daemon.

使用Systemctl控制并管理挂载点

17. 列出所有系统挂载点

[root@CTU1000094955 ~]# systemctl list-unit-files --type=mount

UNIT FILE                     STATE

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  

 unit files listed.

18. 挂载、卸载、重新挂载、重载系统挂载点并检查系统中挂载点状态

[root@CTU1000094955 ~]# systemctl start tmp.mount

[root@CTU1000094955 ~]# systemctl stop tmp.mount

[root@CTU1000094955 ~]# systemctl reload tmp.mount

Job for tmp.mount invalid.

[root@CTU1000094955 ~]# systemctl status tmp.mount

?.tmp.mount - Temporary Directory

   Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled; vendor preset: disabled)

   Active: inactive (dead) since Sat -- :: CST; 25s ago

    Where: /tmp

     What: tmpfs

     Docs: man:hier()

           http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems

  Process:  ExecUnmount=/bin/umount /tmp -n (code=exited, status=/SUCCESS)

  Process:  ExecMount=/bin/mount tmpfs /tmp -n -t tmpfs -o mode=,strictatime (code=exited, status=/SUCCESS)

Nov  :: CTU1000094955 systemd[]: Mounting Temporary Directory...

Nov  :: CTU1000094955 systemd[]: Mounted Temporary Directory.

Nov  :: CTU1000094955 systemd[]: Unmounting Temporary Directory...

Nov  :: CTU1000094955 systemd[]: Unmounted Temporary Directory.

Nov  :: CTU1000094955 systemd[]: Unit tmp.mount cannot be reloaded because it is inactive.

[root@CTU1000094955 ~]# systemctl restart tmp.mount

[root@CTU1000094955 ~]# systemctl status tmp.mount

?.tmp.mount - Temporary Directory

   Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled; vendor preset: disabled)

   Active: active (mounted) since Sat -- :: CST; 2s ago

    Where: /tmp

     What: tmpfs

     Docs: man:hier()

           http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems

  Process:  ExecUnmount=/bin/umount /tmp -n (code=exited, status=/SUCCESS)

  Process:  ExecMount=/bin/mount tmpfs /tmp -n -t tmpfs -o mode=,strictatime (code=exited, status=/SUCCESS)

Nov  :: CTU1000094955 systemd[]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.

Nov  :: CTU1000094955 systemd[]: Mounting Temporary Directory...

Nov  :: CTU1000094955 systemd[]: Mounted Temporary Directory.

[root@CTU1000094955 ~]# systemctl reload tmp.mount

19. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）

[root@CTU1000094955 ~]# systemctl is-active tmp.mount

active

[root@CTU1000094955 ~]# systemctl disable tmp.mount

Removed symlink /etc/systemd/system/local-fs.target.wants/tmp.mount.

[root@CTU1000094955 ~]# systemctl is-active tmp.mount

active

[root@CTU1000094955 ~]# systemctl enable tmp.mount

Failed to execute operation: Access denied

20. 在Linux中屏蔽（让它不能启用）或可见挂载点

[root@CTU1000094955 ~]# systemctl mask tmp.mount

ln -s '/dev/null''/etc/systemd/system/tmp.mount'

[root@CTU1000094955 ~]# systemctl unmask tmp.mount

rm '/etc/systemd/system/tmp.mount'

使用Systemctl控制并管理套接口

21. 列出所有可用系统套接口

[root@CTU1000094955 ~]# systemctl list-unit-files --type=socket

UNIT FILE                    STATE

avahi-daemon.socket          enabled

cups.socket                  enabled

dbus.socket                  static

dm-event.socket              enabled

iscsid.socket                enabled

iscsiuio.socket              enabled

libvirtd.socket              static

lldpad.socket                disabled

lvm2-lvmetad.socket          enabled

lvm2-lvmpolld.socket         enabled

rpcbind.socket               enabled

rsyncd.socket                disabled

sshd.socket                  disabled

syslog.socket                static

systemd-initctl.socket       static

systemd-journald.socket      static

systemd-networkd.socket      disabled

systemd-shutdownd.socket     static

systemd-udevd-control.socket static

systemd-udevd-kernel.socket  static

virtlockd.socket             disabled

 unit files listed.

22. 在Linux中启动、重启、停止、重载套接口并检查其状态

[root@CTU1000094955 ~]# systemctl start sshd.socket

[root@CTU1000094955 ~]# systemctl restart sshd.socket

Failed to restart sshd.socket: Transaction contains conflicting jobs 'restart' and 'stop' for sshd-keygen.service. Probably contradicting requirement dependencies configured.

[root@CTU1000094955 ~]# systemctl status sshd.socket
?.sshd.socket - OpenSSH Server Socket

   Loaded: loaded (/usr/lib/systemd/system/sshd.socket; disabled; vendor preset: disabled)

   Active: active (listening) since Sat -- :: CST; 22s ago

     Docs: man:sshd()

           man:sshd_config()

   Listen: [::]: (Stream)

 Accepted: ; Connected: 

Nov  :: CTU1000094955 systemd[]: Listening on OpenSSH Server Socket.

Nov  :: CTU1000094955 systemd[]: Starting OpenSSH Server Socket.

[root@CTU1000094955 ~]# systemctl stop sshd.socket

[root@CTU1000094955 ~]# systemctl reload sshd.socket

Failed to reload sshd.socket: Job type reload is not applicable for unit sshd.socket.

[root@CTU1000094955 ~]# systemctl status sshd.socket

?.sshd.socket - OpenSSH Server Socket

   Loaded: loaded (/usr/lib/systemd/system/sshd.socket; disabled; vendor preset: disabled)

   Active: inactive (dead) since Sat -- :: CST; 19s ago

     Docs: man:sshd()

           man:sshd_config()

   Listen: [::]: (Stream)

 Accepted: ; Connected: 

Nov  :: CTU1000094955 systemd[]: Listening on OpenSSH Server Socket.

Nov  :: CTU1000094955 systemd[]: Starting OpenSSH Server Socket.

Nov  :: CTU1000094955 systemd[]: Closed OpenSSH Server Socket.

Nov  :: CTU1000094955 systemd[]: Stopping OpenSSH Server Socket.

24. 屏蔽（使它不能启动）或显示套接口

[root@CTU1000094955 ~]# systemctl mask sshd.socket

Created symlink from /etc/systemd/system/sshd.socket to /dev/null.

[root@CTU1000094955 ~]# systemctl unmask sshd.socket

Removed symlink /etc/systemd/system/sshd.socket.

服务的CPU利用率（分配额）

25. 获取当前某个服务的CPU分配额（如httpd）

[root@CTU1000094955 ~]# systemctl show -p CPUShares httpd.service

CPUShares=

　　注意：各个服务的默认CPU分配份额=1024，你可以增加/减少某个进程的CPU分配份额。

26. 将某个服务（httpd.service）的CPU分配份额限制为2000 CPUShares/

[root@CTU1000094955 ~]# systemctl set-property httpd.service CPUShares= 
# systemctl show -p CPUShares httpd.service 
CPUShares=

　　注意：当你为某个服务设置CPUShares，会自动创建一个以服务名命名的目录（如 httpd.service），里面包含了一个名为90-CPUShares.conf的文件，该文件含有CPUShare限制信息，你可以通过以下方式查看该文件：

[root@CTU1000094955 ~]# vi /etc/systemd/system/httpd.service.d/-CPUShares.conf 
[Service] 
CPUShares=

27. 检查某个服务的所有配置细节

[root@CTU1000094955 ~]# systemctl show httpd

Restart=no

NotifyAccess=none

RestartUSec=100ms

TimeoutStartUSec=1min 30s

TimeoutStopUSec=1min 30s

WatchdogUSec=

WatchdogTimestampMonotonic=

StartLimitInterval=

StartLimitBurst=

StartLimitAction=none

FailureAction=none
... ...  中间省略部分内容

28. 分析某个服务（httpd）的关键链

[root@CTU1000094955 ~]# systemd-analyze critical-chain firewalld.service

The time after the unit is active or started is printed after the "@" character.

The time the unit takes to start is printed after the "+" character.

firewalld.service +380ms

?..basic.target @.903s

  ?..sockets.target @.903s

    ?..rpcbind.socket @.903s

      ?..sysinit.target @.895s

        ?..systemd-update-utmp.service @.877s +16ms

          ?..auditd.service @.738s +135ms

            ?..systemd-tmpfiles-setup.service @.661s +73ms

              ?..rhel-import-state.service @.526s +134ms

                ?..local-fs.target @.525s

                  ?..run-user-.mount @.041s

                    ?..local-fs-pre.target @.615s

                      ?..systemd-tmpfiles-setup-dev.service @.519s +92ms

                        ?..kmod-static-nodes.service @.473s +44ms

                          ?..systemd-journald.socket

                            ?..-.slice

29. 获取某个服务（httpd）的依赖性列表

[root@CTU1000094955 ~]# systemctl list-dependencies firewalld.service

firewalld.service

?.?..system.slice

?.?..basic.target

?.  ?..alsa-restore.service

?.  ?..alsa-state.service

  ?.?.....

?.  ?..microcode.service

?.  ?..rhel-autorelabel-mark.service

?.  ?..rhel-autorelabel.service

?.  ?..rhel-configure.service

?.  ?..rhel-dmesg.service

?.  ?..rhel-loadmodules.service

?.  ?..paths.target

?.  ?..slices.target

... ....  后面省略部分内容

30. 按等级列出控制组

[root@CTU1000094955 ~]# systemd-cgls

?.. /usr/lib/systemd/systemd --switched-root --system --deserialize

?..user.slice

?.?..user-.slice

?.?.?..session-c1.scope

?.?.  ?.. gdm-session-worker [pam/gdm-launch-environment]

?.?.  ?.. /usr/bin/gnome-session --autostart /usr/share/gdm/greeter/autostart --session gnome-initial-setup

?.?.  ?.. /usr/bin/dbus-launch --exit-with-session /usr/bin/gnome-session --autostart /usr/share/gdm/greeter/autostart --session gnome-initial-setup

?.?.  ?.. /bin/dbus-daemon --fork --print-pid  --print-address  --session

?.?.  ?.. /usr/libexec/at-spi-bus-launcher

?.?.  ?.. /bin/dbus-daemon --config-file=/etc/at-spi2/accessibility.conf --nofork --print-address

?.?.  ?.. /usr/libexec/at-spi2-registryd --use-gnome-session

?.?.  ?.. gnome-shell --mode=initial-setup

...  ...  中间省略部分内容

?.?.  ?.. /usr/libexec/ibus-engine-simple

?.?.  ?.. gnome-keyring-daemon --unlock

?.?..user-.slice

31. 按CPU、内存、输入和输出列出控制组

[root@CTU1000094955 ~]# systemd-cgtop

Path                                                                                                                                                    Tasks   %CPU   Memory  Input/s Output/s

/                                                                                                                                                               -     .8G        -        -

/system.slice/ModemManager.service                                                                                                                                -        -        -        -

/system.slice/NetworkManager.service                                                                                                                              -        -        -        -

/system.slice/abrt-oops.service                                                                                                                                   -        -        -        -

/system.slice/abrt-xorg.service                                                                                                                                   -        -        -        -

/system.slice/abrtd.service                                                                                                                                       -        -        -        -

/system.slice/accounts-daemon.service                                                                                                                             -        -        -        -

/system.slice/alsa-state.service                                                                                                                                  -        -        -        -

/system.slice/atd.service                                                                                                                                         -        -        -        -

/system.slice/auditd.service                                                                                                                                      -        -        -        -

控制系统运行等级

32. 启动系统救援模式

[root@CTU1000094955 ~]# systemctl rescue

Broadcast message from root@tecmint on pts/(Wed2015--:: IST):

The system is going down to rescue mode NOW!

33. 进入紧急模式

[root@CTU1000094955 ~]# systemctl emergency

Welcome to emergency mode!After logging in, type "journalctl -xb" to view

system logs,"systemctl reboot" to reboot,"systemctl default" to try again

to boot intodefault mode.

34. 列出当前使用的运行等级

　　运行等级说明如下。

Runlevel 0 : 关闭系统　　shutdown.target　　
Runlevel 1 : 紧急？维护模式　　emergency.target
Runlevel 2 : 救援？维护模式　　rescure.target
Runlevel 3 : 多用户，无图形系统　　multi-user.target
Runlevel 4 : 多用户，无图形系统　　无
Runlevel 5 : 多用户，图形化系统　　graphical.target
Runlevel 6 : 关闭并重启机器　　无

[root@CTU1000094955 ~]# systemctl get-default

graphical.target

35. 启动运行等级5，即图形模式

# systemctl isolate runlevel5.target

或

# systemctl isolate graphical.target

[root@CTU1000094955 ~]# systemctl isolate runlevel5.target

PolicyKit daemon disconnected from the bus.

We are no longer a registered authentication agent.

36. 启动运行等级3，即多用户模式（命令行）

# systemctl isolate runlevel3.target

或

# systemctl isolate multiuser.target

36. 设置多用户模式或图形模式为默认运行等级

# systemctl set-default runlevel3.target

# systemctl set-default runlevel5.target

37. 重启、停止、挂起、休眠系统或使系统进入混合睡眠

# systemctl reboot　　重新启动

# systemctl halt

# systemctl suspend　　进入睡眠模式

# systemctl hibernate　　进入休眠模式

# systemctl hybrid-sleep
# systemctl rescue　　强制进入救援模式
# systemctl emergency　　强制进入紧急救援模式
# systemctl poweroff　　系统关机

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