系统运维-16-2-Systemd基本使用方法

0.基础知识准备。需要先了解系统的启动基本流程：

POST  --->  Boot Sequence  --->  Bootloader  --->  kernel + iniramfs  (initrd)  --->rootfs  --->  /sbin/init  (centos5:SysV init  /  centos6:Upstart  /  centos7:Systemd)

1.初步了解Systemd。

yum install -y psmisc安装软件包。pstree查看进程树。

[root@lab1 ~]# yum install -y psmisc
[root@lab1 ~]# pstree
systemd─┬─NetworkManager─┬─dhclient
        │                └─2*[{NetworkManager}]
        ├─VGAuthService
        ├─agetty
        ├─auditd───{auditd}
        ├─chronyd
        ├─crond
        ├─dbus-daemon───{dbus-daemon}
        ├─firewalld───{firewalld}
        ├─irqbalance
        ├─lvmetad
        ├─master─┬─pickup
        │        └─qmgr
        ├─polkitd───5*[{polkitd}]
        ├─rsyslogd───2*[{rsyslogd}]
        ├─sshd───sshd───bash───pstree
        ├─systemd-journal
        ├─systemd-logind
        ├─systemd-udevd
        ├─tuned───4*[{tuned}]
        └─vmtoolsd───{vmtoolsd}
 

2.关于控制服务状态。

rpm -qi httpd查看常用的服务httpd的安装情况（没安装的自行安装，这里不列明步骤了）。systemctl start httpd.service启动服务。systemctl status httpd查看服务状态。systemctl stop httpd关闭服务。systemctl status httpd再次查看服务状态。

[root@lab1 ~]# rpm -qi httpd
Name        : httpd
Version     : 2.4.6
Release     : 88.el7.centos
Architecture: x86_64
Install Date: Fri 04 Jan 2019 11:35:44 PM EST
Group       : System Environment/Daemons
Size        : 9817309
License     : ASL 2.0
Signature   : RSA/SHA256, Mon 12 Nov 2018 09:28:53 AM EST, Key ID 24c6a8a7f4a80eb5
Source RPM  : httpd-2.4.6-88.el7.centos.src.rpm
Build Date  : Sun 04 Nov 2018 08:48:57 PM EST
Build Host  : x86-01.bsys.centos.org
Relocations : (not relocatable)
Packager    : CentOS BuildSystem <http://bugs.centos.org>
Vendor      : CentOS
URL         : http://httpd.apache.org/
Summary     : Apache HTTP Server
Description :
The Apache HTTP Server is a powerful, efficient, and extensible
web server.
[root@lab1 ~]# systemctl start httpd.service
[root@lab1 ~]# systemctl status httpd
● httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
   Active: active (running) since Sun 2019-01-06 01:59:33 EST; 13s ago
     Docs: man:httpd(8)
           man:apachectl(8)
 Main PID: 2281 (httpd)
   Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"
   CGroup: /system.slice/httpd.service
           ├─2281 /usr/sbin/httpd -DFOREGROUND
           ├─2282 /usr/sbin/httpd -DFOREGROUND
           ├─2283 /usr/sbin/httpd -DFOREGROUND
           ├─2284 /usr/sbin/httpd -DFOREGROUND
           ├─2285 /usr/sbin/httpd -DFOREGROUND
           └─2286 /usr/sbin/httpd -DFOREGROUND

Jan 06 01:59:32 lab1.example.com systemd[1]: Starting The Apache HTTP Server...
Jan 06 01:59:33 lab1.example.com systemd[1]: Started The Apache HTTP Server.

[root@lab1 ~]# systemctl stop httpd
[root@lab1 ~]# systemctl status httpd
● httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
   Active: inactive (dead)
     Docs: man:httpd(8)
           man:apachectl(8)

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Jan 06 01:59:32 lab1.example.com systemd[1]: Starting The Apache HTTP Server...
Jan 06 01:59:33 lab1.example.com systemd[1]: Started The Apache HTTP Server.
Jan 06 02:01:18 lab1.example.com systemd[1]: Stopping The Apache HTTP Server...
Jan 06 02:01:19 lab1.example.com systemd[1]: Stopped The Apache HTTP Server.
 

3.关于当前服务状态。

systemctl is-active httpd检查服务状态。systemctl start httpd启动服务。systemctl is-active httpd再次检查服务状态。systemctl list-units --type service列出所有活动的服务。systemctl list-units --type service --all列出所有服务的当前状态（包括不活动的服务）。

[root@lab1 ~]# systemctl is-active httpd
unknown
[root@lab1 ~]# systemctl start httpd
[root@lab1 ~]# systemctl is-active httpd
active
[root@lab1 ~]# systemctl list-units --type service | head
UNIT                               LOAD   ACTIVE SUB     DESCRIPTION
auditd.service                     loaded active running Security Auditing Service
chronyd.service                    loaded active running NTP client/server
crond.service                      loaded active running Command Scheduler
dbus.service                       loaded active running D-Bus System Message Bus
firewalld.service                  loaded active running firewalld - dynamic firewall daemon
[email protected]                 loaded active running Getty on tty1
httpd.service                      loaded active running The Apache HTTP Server
irqbalance.service                 loaded active running irqbalance daemon
kdump.service                      loaded active exited  Crash recovery kernel arming
[root@lab1 ~]# systemctl list-units --type service --all | grep inactive | head
  brandbot.service                                      loaded    inactive dead    Flexible Branding Service
  cpupower.service                                      loaded    inactive dead    Configure CPU power related settings
● display-manager.service                               not-found inactive dead    display-manager.service
  dm-event.service                                      loaded    inactive dead    Device-mapper event daemon
  dracut-shutdown.service                               loaded    inactive dead    Restore /run/initramfs
  ebtables.service                                      loaded    inactive dead    Ethernet Bridge Filtering tables
  emergency.service                                     loaded    inactive dead    Emergency Shell
● exim.service                                          not-found inactive dead    exim.service
● ip6tables.service                                     not-found inactive dead    ip6tables.service
● ipset.service                                         not-found inactive dead    ipset.service

4.关于开机启动状态。

systemctl status httpd查看当前状态（开机不启动）。systemctl enable httpd设置为开机启动。systemctl status httpd再次查看当前状态（开机启动）。systemctl list-unit-files --type service查看所有服务的开机启动状态。systemctl is-enabled httpd查看是否处于开机启动状态。

[root@lab1 ~]# systemctl status httpd | grep loaded
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
[root@lab1 ~]# systemctl enable httpd
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
[root@lab1 ~]# systemctl status httpd | grep loaded
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
[root@lab1 ~]# systemctl list-unit-files --type service | head
UNIT FILE                                     STATE   
arp-ethers.service                            disabled
auditd.service                                enabled 
[email protected]                               enabled 
blk-availability.service                      disabled
brandbot.service                              static  
[email protected]                        static  
chrony-wait.service                           disabled
chronyd.service                               enabled 
console-getty.service                         disabled

[root@lab1 ~]# systemctl is-enabled httpd
enabled

5.关于运行级别

systemctl list-units --type target查看目前处于活动状态的运行级别。systemctl list-units --type target --all查看所有的运行级别。

[root@lab1 ~]# systemctl list-units --type target
UNIT                  LOAD   ACTIVE SUB    DESCRIPTION
basic.target          loaded active active Basic System
bluetooth.target      loaded active active Bluetooth
cryptsetup.target     loaded active active Encrypted Volumes
getty.target          loaded active active Login Prompts
local-fs-pre.target   loaded active active Local File Systems (Pre)
local-fs.target       loaded active active Local File Systems
multi-user.target     loaded active active Multi-User System
network-online.target loaded active active Network is Online
network-pre.target    loaded active active Network (Pre)
network.target        loaded active active Network
paths.target          loaded active active Paths
remote-fs.target      loaded active active Remote File Systems
slices.target         loaded active active Slices
sockets.target        loaded active active Sockets
sound.target          loaded active active Sound Card
swap.target           loaded active active Swap
sysinit.target        loaded active active System Initialization
timers.target         loaded active active Timers

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.

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

[root@lab1 ~]# systemctl list-units --type target --all
  UNIT                   LOAD      ACTIVE   SUB    DESCRIPTION
  basic.target           loaded    active   active Basic System
  bluetooth.target       loaded    active   active Bluetooth
  cryptsetup.target      loaded    active   active Encrypted Volumes
  emergency.target       loaded    inactive dead   Emergency Mode
  final.target           loaded    inactive dead   Final Step
  getty.target           loaded    active   active Login Prompts
  graphical.target       loaded    inactive dead   Graphical Interface
  local-fs-pre.target    loaded    active   active Local File Systems (Pre)
  local-fs.target        loaded    active   active Local File Systems
  multi-user.target      loaded    active   active Multi-User System
  network-online.target  loaded    active   active Network is Online
  network-pre.target     loaded    active   active Network (Pre)
  network.target         loaded    active   active Network
  nss-lookup.target      loaded    inactive dead   Host and Network Name Lookups
  nss-user-lookup.target loaded    inactive dead   User and Group Name Lookups
  paths.target           loaded    active   active Paths
  remote-fs-pre.target   loaded    inactive dead   Remote File Systems (Pre)
  remote-fs.target       loaded    active   active Remote File Systems
  rescue.target          loaded    inactive dead   Rescue Mode
  shutdown.target        loaded    inactive dead   Shutdown
  slices.target          loaded    active   active Slices
  sockets.target         loaded    active   active Sockets
  sound.target           loaded    active   active Sound Card
  swap.target            loaded    active   active Swap
  sysinit.target         loaded    active   active System Initialization
● syslog.target          not-found inactive dead   syslog.target
  time-sync.target       loaded    inactive dead   System Time Synchronized
  timers.target          loaded    active   active Timers
  umount.target          loaded    inactive dead   Unmount All Filesystems

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.
[root@lab1 ~]# systemctl get-default
multi-user.target
 

6.关于依赖关系。

systemctl list-dependencies httpd可以查看某一服务其依赖的其他服务。

[root@lab1 ~]# systemctl list-dependencies httpd
httpd.service
● ├─-.mount
● ├─system.slice
● └─basic.target
●   ├─microcode.service
●   ├─rhel-autorelabel-mark.service
●   ├─rhel-autorelabel.service
●   ├─rhel-configure.service
●   ├─rhel-dmesg.service
●   ├─rhel-loadmodules.service
●   ├─[email protected]
●   ├─paths.target
●   ├─slices.target
●   │ ├─-.slice
●   │ └─system.slice
●   ├─sockets.target
●   │ ├─dbus.socket
●   │ ├─dm-event.socket
●   │ ├─systemd-initctl.socket
●   │ ├─systemd-journald.socket
●   │ ├─systemd-shutdownd.socket
●   │ ├─systemd-udevd-control.socket
●   │ └─systemd-udevd-kernel.socket
●   ├─sysinit.target
●   │ ├─dev-hugepages.mount
●   │ ├─dev-mqueue.mount
●   │ ├─kmod-static-nodes.service
●   │ ├─lvm2-lvmetad.socket
●   │ ├─lvm2-lvmpolld.socket
●   │ ├─lvm2-monitor.service
●   │ ├─plymouth-read-write.service
●   │ ├─plymouth-start.service
●   │ ├─proc-sys-fs-binfmt_misc.automount
●   │ ├─sys-fs-fuse-connections.mount
●   │ ├─sys-kernel-config.mount
●   │ ├─sys-kernel-debug.mount

7.关于手动编辑文件

cd /usr/lib/systemd/system转到指定目录下。cat httpd.service | grep ^# -v | grep ^$ -v查看某一服务其配置文件的特定格式（照此格式可以手动编辑服务的配置文件）。
[root@lab1 ~]# cd /usr/lib/systemd/system
[root@lab1 system]# cat httpd.service | grep ^# -v | grep ^$ -v
[Unit]
Description=The Apache HTTP Server
After=network.target remote-fs.target nss-lookup.target
Documentation=man:httpd(8)
Documentation=man:apachectl(8)
[Service]
Type=notify
EnvironmentFile=/etc/sysconfig/httpd
ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND
ExecReload=/usr/sbin/httpd $OPTIONS -k graceful
ExecStop=/bin/kill -WINCH ${MAINPID}
KillSignal=SIGCONT
PrivateTmp=true
[Install]
WantedBy=multi-user.target