Systemctl是一個(gè)systemd工具，主要負(fù)責(zé)控制systemd系統(tǒng)和服務(wù)管理器。

Systemd是一個(gè)系統(tǒng)管理守護(hù)進(jìn)程、工具和庫的集合，用于取代System V初始進(jìn)程。Systemd的功能是用于集中管理和配置類UNIX系統(tǒng)。

在Linux生態(tài)系統(tǒng)中，Systemd被部署到了大多數(shù)的標(biāo)準(zhǔn)Linux發(fā)行版中，只有為數(shù)不多的幾個(gè)發(fā)行版尚未部署。Systemd通常是所有其它守護(hù)進(jìn)程的父進(jìn)程，但并非總是如此。

使用Systemctl管理Linux服務(wù)

本文旨在闡明在運(yùn)行systemd的系統(tǒng)上“如何控制系統(tǒng)和服務(wù)”。

Systemd初體驗(yàn)和Systemctl基礎(chǔ)

1. 首先檢查你的系統(tǒng)中是否安裝有systemd并確定當(dāng)前安裝的版本

# systemd --version

systemd 215
+PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR

上例中很清楚地表明，我們安裝了215版本的systemd。

2. 檢查systemd和systemctl的二進(jìn)制文件和庫文件的安裝位置

# whereis systemd
systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz

# whereis systemctl
systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz

3. 檢查systemd是否運(yùn)行

# ps -eaf | grep [s]ystemd

root         1     0  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
root       444     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-journald
root       469     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-udevd
root       555     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-logind
dbus       556     1  0 16:27 ?        00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation

注意：systemd是作為父進(jìn)程（PID=1）運(yùn)行的。在上面帶（-e）參數(shù)的ps命令輸出中，選擇所有進(jìn)程，（-a）選擇除會(huì)話前導(dǎo)外的所有進(jìn)程，并使用（-f）參數(shù)輸出完整格式列表（即 -eaf）。

也請(qǐng)注意上例中后隨的方括號(hào)和例子中剩余部分。方括號(hào)表達(dá)式是grep的字符類表達(dá)式的一部分。

4. 分析systemd啟動(dòng)進(jìn)程

# systemd-analyze
Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s

5. 分析啟動(dòng)時(shí)各個(gè)進(jìn)程花費(fèi)的時(shí)間

# systemd-analyze blame

8.565s mariadb.service
7.991s webmin.service
6.095s postfix.service
4.311s httpd.service
3.926s firewalld.service
3.780s kdump.service
3.238s tuned.service
1.712s network.service
1.394s lvm2-monitor.service
1.126s systemd-logind.service
....

6. 分析啟動(dòng)時(shí)的關(guān)鍵鏈

# 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.

multi-user.target @20.222s
└─mariadb.service @11.657s +8.565s
  └─network.target @11.168s
    └─network.service @9.456s +1.712s
      └─NetworkManager.service @8.858s +596ms
        └─firewalld.service @4.931s +3.926s
          └─basic.target @4.916s
            └─sockets.target @4.916s
              └─dbus.socket @4.916s
                └─sysinit.target @4.905s
                  └─systemd-update-utmp.service @4.864s +39ms
                    └─auditd.service @4.563s +301ms
                      └─systemd-tmpfiles-setup.service @4.485s +69ms
                        └─rhel-import-state.service @4.342s +142ms
                          └─local-fs.target @4.324s
                            └─boot.mount @4.286s +31ms
                              └─systemd-fsck@dev-disk-by/x2duuid-79f594ad/x2da332/x2d4730/x2dbb5f/x2d85d19608096
                                └─dev-disk-by/x2duuid-79f594ad/x2da332/x2d4730/x2dbb5f/x2d85d196080964.device @4

重要：Systemctl接受服務(wù)（.service），掛載點(diǎn)（.mount），套接口（.socket）和設(shè)備（.device）作為單元。

7. 列出所有可用單元

# systemctl list-unit-files

UNIT FILE                                   STATE  
proc-sys-fs-binfmt_misc.automount           static 
dev-hugepages.mount                         static 
dev-mqueue.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
brandbot.path                               disabled
.....

8. 列出所有運(yùn)行中單元

# systemctl list-units

UNIT                                        LOAD   ACTIVE SUB       DESCRIPTION
proc-sys-fs-binfmt_misc.automount           loaded active waiting   Arbitrary Executable File Formats File Syste
sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged   VBOX_CD-ROM
sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged   PRO/1000 MT Desktop Adapter
sys-devices-pc...00:05.0-sound-card0.device loaded active plugged   82801AA AC'97 Audio Controller
sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged   VBOX_HARDDISK
sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged   LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8
sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged   VBOX_HARDDISK
sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS0
sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS1
sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS2
sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS3
sys-devices-virtual-block-dm/x2d0.device    loaded active plugged   /sys/devices/virtual/block/dm-0
sys-devices-virtual-block-dm/x2d1.device    loaded active plugged   /sys/devices/virtual/block/dm-1
sys-module-configfs.device                  loaded active plugged   /sys/module/configfs
...

9. 列出所有失敗單元

# systemctl --failed

UNIT          LOAD   ACTIVE SUB    DESCRIPTION
kdump.service loaded failed failed Crash recovery kernel arming

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.

1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.

10. 檢查某個(gè)單元（如 cron.service）是否啟用

# systemctl is-enabled crond.service

enabled

11. 檢查某個(gè)單元或服務(wù)是否運(yùn)行

# systemctl status firewalld.service

firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
   Active: active (running) since Tue 2015-04-28 16:27:55 IST; 34min ago
Main PID: 549 (firewalld)
   CGroup: /system.slice/firewalld.service
           └─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

Apr 28 16:27:51 tecmint systemd[1]: Starting firewalld - dynamic firewall daemon...
Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.

使用Systemctl控制并管理服務(wù)

12. 列出所有服務(wù)（包括啟用的和禁用的）

# systemctl list-unit-files --type=service

UNIT FILE                                   STATE  
arp-ethers.service                          disabled
auditd.service                              enabled
autovt@.service                             disabled
blk-availability.service                    disabled
brandbot.service                            static 
collectd.service                            disabled
console-getty.service                       disabled
console-shell.service                       disabled
cpupower.service                            disabled
crond.service                               enabled
dbus-org.fedoraproject.FirewallD1.service   enabled
....

13. Linux中如何啟動(dòng)、重啟、停止、重載服務(wù)以及檢查服務(wù)（如 httpd.service）狀態(tài)

# systemctl start httpd.service
# systemctl restart httpd.service
# systemctl stop httpd.service
# systemctl reload httpd.service
# systemctl status httpd.service

httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
   Active: active (running) since Tue 2015-04-28 17:21:30 IST; 6s ago
  Process: 2876 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 2881 (httpd)
   Status: "Processing requests..."
   CGroup: /system.slice/httpd.service
           ├─2881 /usr/sbin/httpd -DFOREGROUND
           ├─2884 /usr/sbin/httpd -DFOREGROUND
           ├─2885 /usr/sbin/httpd -DFOREGROUND
           ├─2886 /usr/sbin/httpd -DFOREGROUND
           ├─2887 /usr/sbin/httpd -DFOREGROUND
           └─2888 /usr/sbin/httpd -DFOREGROUND

Apr 28 17:21:30 tecmint systemd[1]: Starting The Apache HTTP Server...
Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssage
Apr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server.
Hint: Some lines were ellipsized, use -l to show in full.

注意：當(dāng)我們使用systemctl的start，restart，stop和reload命令時(shí)，我們不會(huì)從終端獲取到任何輸出內(nèi)容，只有status命令可以打印輸出。

14. 如何激活服務(wù)并在啟動(dòng)時(shí)啟用或禁用服務(wù)（即系統(tǒng)啟動(dòng)時(shí)自動(dòng)啟動(dòng)服務(wù)）

# systemctl is-active httpd.service
# systemctl enable httpd.service
# systemctl disable httpd.service

15. 如何屏蔽（讓它不能啟動(dòng)）或顯示服務(wù)（如 httpd.service）

# systemctl mask httpd.service
ln -s '/dev/null' '/etc/systemd/system/httpd.service'

# systemctl unmask httpd.service
rm '/etc/systemd/system/httpd.service'

16. 使用systemctl命令殺死服務(wù)

# systemctl kill httpd
# systemctl status httpd

httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
   Active: failed (Result: exit-code) since Tue 2015-04-28 18:01:42 IST; 28min ago
Main PID: 2881 (code=exited, status=0/SUCCESS)
   Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"

Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226
Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state.
Hint: Some lines were ellipsized, use -l to show in full.

使用Systemctl控制并管理掛載點(diǎn)

17. 列出所有系統(tǒng)掛載點(diǎn)

# systemctl list-unit-files --type=mount

UNIT FILE                     STATE  
dev-hugepages.mount           static 
dev-mqueue.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

18. 掛載、卸載、重新掛載、重載系統(tǒng)掛載點(diǎn)并檢查系統(tǒng)中掛載點(diǎn)狀態(tài)

# systemctl start tmp.mount
# systemctl stop tmp.mount
# systemctl restart tmp.mount
# systemctl reload tmp.mount
# systemctl status tmp.mount

tmp.mount - Temporary Directory
   Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)
   Active: active (mounted) since Tue 2015-04-28 17:46:06 IST; 2min 48s ago
    Where: /tmp
     What: tmpfs
     Docs: man:hier(7)

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

  Process: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS)

Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory...
Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.
Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.

19. 在啟動(dòng)時(shí)激活、啟用或禁用掛載點(diǎn)（系統(tǒng)啟動(dòng)時(shí)自動(dòng)掛載）

# systemctl is-active tmp.mount
# systemctl enable tmp.mount
# systemctl disable  tmp.mount

20. 在Linux中屏蔽（讓它不能啟用）或可見掛載點(diǎn)

# systemctl mask tmp.mount

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

# systemctl unmask tmp.mount

rm '/etc/systemd/system/tmp.mount'

使用Systemctl控制并管理套接口

21. 列出所有可用系統(tǒng)套接口

# systemctl list-unit-files --type=socket

UNIT FILE                    STATE  
dbus.socket                  static 
dm-event.socket              enabled
lvm2-lvmetad.socket          enabled
rsyncd.socket                disabled
sshd.socket                  disabled
syslog.socket                static 
systemd-initctl.socket       static 
systemd-journald.socket      static 
systemd-shutdownd.socket     static 
systemd-udevd-control.socket static 
systemd-udevd-kernel.socket  static 

11 unit files listed.

22. 在Linux中啟動(dòng)、重啟、停止、重載套接口并檢查其狀態(tài)

# systemctl start cups.socket
# systemctl restart cups.socket
# systemctl stop cups.socket
# systemctl reload cups.socket
# systemctl status cups.socket

cups.socket - CUPS Printing Service Sockets
   Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled)
   Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago
   Listen: /var/run/cups/cups.sock (Stream)

Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets.
Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.

23. 在啟動(dòng)時(shí)激活套接口，并啟用或禁用它（系統(tǒng)啟動(dòng)時(shí)自啟動(dòng)）

# systemctl is-active cups.socket
# systemctl enable cups.socket
# systemctl disable cups.socket

24. 屏蔽（使它不能啟動(dòng)）或顯示套接口

# systemctl mask cups.socket
ln -s '/dev/null' '/etc/systemd/system/cups.socket'

# systemctl unmask cups.socket
rm '/etc/systemd/system/cups.socket'

服務(wù)的CPU利用率（分配額）

25. 獲取當(dāng)前某個(gè)服務(wù)的CPU分配額（如httpd）

# systemctl show -p CPUShares httpd.service

CPUShares=1024

注意：各個(gè)服務(wù)的默認(rèn)CPU分配份額=1024，你可以增加/減少某個(gè)進(jìn)程的CPU分配份額。

26. 將某個(gè)服務(wù)（httpd.service）的CPU分配份額限制為2000 CPUShares/

# systemctl set-property httpd.service CPUShares=2000
# systemctl show -p CPUShares httpd.service

CPUShares=2000

注意：當(dāng)你為某個(gè)服務(wù)設(shè)置CPUShares，會(huì)自動(dòng)創(chuàng)建一個(gè)以服務(wù)名命名的目錄（如 httpd.service），里面包含了一個(gè)名為90-CPUShares.conf的文件，該文件含有CPUShare限制信息，你可以通過以下方式查看該文件：

# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf

[Service]
CPUShares=2000

27. 檢查某個(gè)服務(wù)的所有配置細(xì)節(jié)

# systemctl show httpd

Id=httpd.service
Names=httpd.service
Requires=basic.target
Wants=system.slice
WantedBy=multi-user.target
Conflicts=shutdown.target
Before=shutdown.target multi-user.target
After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice
Description=The Apache HTTP Server
LoadState=loaded
ActiveState=active
SubState=running
FragmentPath=/usr/lib/systemd/system/httpd.service
....

28. 分析某個(gè)服務(wù)（httpd）的關(guān)鍵鏈

# systemd-analyze critical-chain httpd.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.

httpd.service +142ms
└─network.target @11.168s
  └─network.service @9.456s +1.712s
    └─NetworkManager.service @8.858s +596ms
      └─firewalld.service @4.931s +3.926s
        └─basic.target @4.916s
          └─sockets.target @4.916s
            └─dbus.socket @4.916s
              └─sysinit.target @4.905s
                └─systemd-update-utmp.service @4.864s +39ms
                  └─auditd.service @4.563s +301ms
                    └─systemd-tmpfiles-setup.service @4.485s +69ms
                      └─rhel-import-state.service @4.342s +142ms
                        └─local-fs.target @4.324s
                          └─boot.mount @4.286s +31ms
                            └─systemd-fsck@dev-disk-by/x2duuid-79f594ad/x2da332/x2d4730/x2dbb5f/x2d85d196080964.service @4.092s +149ms
                              └─dev-disk-by/x2duuid-79f594ad/x2da332/x2d4730/x2dbb5f/x2d85d196080964.device @4.092s

29. 獲取某個(gè)服務(wù)（httpd）的依賴性列表

# systemctl list-dependencies httpd.service

httpd.service
├─system.slice
└─basic.target
  ├─firewalld.service
  ├─microcode.service
  ├─rhel-autorelabel-mark.service
  ├─rhel-autorelabel.service
  ├─rhel-configure.service
  ├─rhel-dmesg.service
  ├─rhel-loadmodules.service
  ├─paths.target
  ├─slices.target
  │ ├─-.slice
  │ └─system.slice
  ├─sockets.target
  │ ├─dbus.socket
....

30. 按等級(jí)列出控制組

# systemd-cgls

├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
├─user.slice
│ └─user-0.slice
│   └─session-1.scope
│     ├─2498 sshd: root@pts/0   
│     ├─2500 -bash
│     ├─4521 systemd-cgls
│     └─4522 systemd-cgls
└─system.slice
  ├─httpd.service
  │ ├─4440 /usr/sbin/httpd -DFOREGROUND
  │ ├─4442 /usr/sbin/httpd -DFOREGROUND
  │ ├─4443 /usr/sbin/httpd -DFOREGROUND
  │ ├─4444 /usr/sbin/httpd -DFOREGROUND
  │ ├─4445 /usr/sbin/httpd -DFOREGROUND
  │ └─4446 /usr/sbin/httpd -DFOREGROUND
  ├─polkit.service
  │ └─721 /usr/lib/polkit-1/polkitd --no-debug
....

31. 按CPU、內(nèi)存、輸入和輸出列出控制組

# systemd-cgtop

Path                                                              Tasks   %CPU   Memory  Input/s Output/s

/                                                                    83    1.0   437.8M        -        -
/system.slice                                                         -    0.1        -        -        -
/system.slice/mariadb.service                                         2    0.1        -        -        -
/system.slice/tuned.service                                           1    0.0        -        -        -
/system.slice/httpd.service                                           6    0.0        -        -        -
/system.slice/NetworkManager.service                                  1      -        -        -        -
/system.slice/atop.service                                            1      -        -        -        -
/system.slice/atopacct.service                                        1      -        -        -        -
/system.slice/auditd.service                                          1      -        -        -        -
/system.slice/crond.service                                           1      -        -        -        -
/system.slice/dbus.service                                            1      -        -        -        -
/system.slice/firewalld.service                                       1      -        -        -        -
/system.slice/lvm2-lvmetad.service                                    1      -        -        -        -
/system.slice/polkit.service                                          1      -        -        -        -
/system.slice/postfix.service                                         3      -        -        -        -
/system.slice/rsyslog.service                                         1      -        -        -        -
/system.slice/system-getty.slice/getty@tty1.service                   1      -        -        -        -
/system.slice/systemd-journald.service                                1      -        -        -        -
/system.slice/systemd-logind.service                                  1      -        -        -        -
/system.slice/systemd-udevd.service                                   1      -        -        -        -
/system.slice/webmin.service                                          1      -        -        -        -
/user.slice/user-0.slice/session-1.scope                              3      -        -        -        -

控制系統(tǒng)運(yùn)行等級(jí)

32. 啟動(dòng)系統(tǒng)救援模式

# systemctl rescue

Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):

The system is going down to rescue mode NOW!

33. 進(jìn)入緊急模式

# 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 into default mode.

34. 列出當(dāng)前使用的運(yùn)行等級(jí)

# systemctl get-default

multi-user.target

35. 啟動(dòng)運(yùn)行等級(jí)5，即圖形模式

# systemctl isolate runlevel5.target
或
# systemctl isolate graphical.target

36. 啟動(dòng)運(yùn)行等級(jí)3，即多用戶模式（命令行）

# systemctl isolate runlevel3.target
或
# systemctl isolate multiuser.target

36. 設(shè)置多用戶模式或圖形模式為默認(rèn)運(yùn)行等級(jí)

# systemctl set-default runlevel3.target

# systemctl set-default runlevel5.target

37. 重啟、停止、掛起、休眠系統(tǒng)或使系統(tǒng)進(jìn)入混合睡眠

# systemctl reboot

# systemctl halt

# systemctl suspend

# systemctl hibernate

# systemctl hybrid-sleep

對(duì)于不知運(yùn)行等級(jí)為何物的人，說明如下。

• Runlevel 0 : 關(guān)閉系統(tǒng)

• Runlevel 1 : 救援？維護(hù)模式

• Runlevel 3 : 多用戶，無圖形系統(tǒng)

• Runlevel 4 : 多用戶，無圖形系統(tǒng)

• Runlevel 5 : 多用戶，圖形化系統(tǒng)

• Runlevel 6 : 關(guān)閉并重啟機(jī)器

到此為止吧。保持連線，進(jìn)行評(píng)論。別忘了在下面的評(píng)論中為我們提供一些有價(jià)值的反饋哦。喜歡我們、與我們分享，求擴(kuò)散。