linux的服务与如何建立自己的服务

- 启动:/etc/init.d/daemon start
- 关闭:/etc/init.d/daemon stop
- 重新启动:/etc/init.d/daemon restart
- 状态观察:/etc/init.d/daemon status服务启动的分类:
init 服务的分类中，依据服务是独立启动或被一只总管程序管理而分为两大类:

- 独立启动模式 (stand alone):服务独立启动，该服务直接常驻于内存中，提供本机或用户的服务行为，反应速度快。
- 总管程序 (super daemon):由特殊的 xinetd 或 inetd 这两个总管程序提供 socket 对应或 port 对应的管理。当没有用户要求某 socket 或 port 时， 所需要的服务是不会被启动的。若有用户要求时， xinetd 总管才会去唤醒相对应的服务程序。当该要求结束时，这个服务也会被结束掉~ 因为透过 xinetd 所总管，因此这个家伙就被称为 super daemon。好处是可以透过 super daemon 来进行服务的时程、联机需求等的控制，缺点是唤醒服务需要一点时间的延迟。服务的相依性问题:
服务是可能会有相依性的~例如，你要启动网络服务，但是系统没有网络，那怎么可能可以唤醒网络服务呢?如果你需要联机到外部取得认证服务器的联机，但该联机需要另一个 A 服务的需求，问题是，A 服务没有启动，因此，你的认证服务就不可能会成功启动的!这就是所谓的服务相依性问题。init 在管理员自己手动处理这些服务时，是没有办法协助相依服务的唤醒的!执行等级的分类:
上面说到 init 是开机后核心主动呼叫的，然后 init 可以根据用户自定义的执行等级 (runlevel) 来唤醒不同的服务，以进入不同的操作界面。基本上 Linux 提供 7 个执行等级，分别是 0, 1, 2...6 ，比较重要的是 1)单人维护模式、3)纯文本模式、5)文字加图形界面。而各个执行等级的启动脚本是透过 /etc/rc.d/rc0-6/SXXdaemon 连结到 /etc/init.d/daemon，连结档名 (SXXdaemon) 的功能为: S 为启动该服务，XX 是数字，为启动的顺序。由于有 SXX 的设定，因此在开机时可以『依序执行』所有需要的服务，同时也能解决相依服务的问题。这点与管理员自己手动处理不太一样就是了。制定执行等级默认要启动的服务:
若要建立如上提到的 SXXdaemon 的话，不需要管理员手动建立连结档，透过如下的指令可以来处理默认启动、预设不启动、观察预设启动否的行为:

- 预设要启动: chkconfig daemon on
- 预设不启动: chkconfig daemon off
- 观察预设为启动否: chkconfig --list daemon执行等级的切换行为:
当你要从纯文本界面 (runlevel 3) 切换到图形界面 (runlevel 5)，不需要手动启动、关闭该执行等级的相关服务，只要『 init 5 』即可切换，init 这小子会主动去分析 /etc/rc.d/rc35.d/ 这两个目录内的脚本，然后启动转换 runlevel 中需要的服务~就完成整体的 runlevel 切换。

[root@study ~]# ll /usr/lib/systemd/system/ | grep -E '(vsftp|multi|cron)'
-rw-r--r--. 1 root root  284 7月  27 2015 crond.service  <--服务-->
-rw-r--r--. 1 root root  597 11月 20 2015 multipathd.service     <--服务-->
-rw-r--r--. 1 root root  492 10月 19 00:48 multi-user.target
drwxr-xr-x. 2 root root 4096 10月 23 15:06 multi-user.target.wants
lrwxrwxrwx. 1 root root   17 10月 23 15:06 runlevel2.target -> multi-user.target
lrwxrwxrwx. 1 root root   17 10月 23 15:06 runlevel3.target -> multi-user.target
lrwxrwxrwx. 1 root root   17 10月 23 15:06 runlevel4.target -> multi-user.target
-rw-r--r--. 1 root root  171 10月 31 2018 vsftpd.service      <--服务-->
-rw-r--r--. 1 root root  184 10月 31 2018 vsftpd@.service
-rw-r--r--. 1 root root   89 10月 31 2018 vsftpd.target
#比较重要的是上头提供的那三行已service结尾的部份!

[root@study ~]# systemctl [command] [unit]
command 主要有:
start     :立刻启动后面接的 unit
stop      :立刻关闭后面接的 unit
restart     :立刻关闭后启动后面接的 unit，亦即执行 stop 再 start 的意思
reload     :不关闭后面接的 unit 的情况下，重载配置文件，让设定生效
enable     :设定下次开机时，后面接的 unit 会被启动
disable     :设定下次开机时，后面接的 unit 不会被启动
status     :目前后面接的这个 unit 的状态，会列出有没有正在执行、开机预设执行否、登录等信息等!
is-active:目前有没有正在运作中
is-enabled:开机时有没有预设要启用这个 unit


#范例一:看看目前 atd 这个服务的状态为何?
[root@study Packages]# systemctl status atd.service 
● atd.service - Job spooling tools
   Loaded: loaded (/usr/lib/systemd/system/atd.service; enabled; vendor preset: enabled)
   Active: active (running) since 一 2019-11-04 19:00:21 CST; 4h 17min ago
 Main PID: 1537 (atd)
   CGroup: /system.slice/atd.service
           └─1537 /usr/sbin/atd -f

11月 04 19:00:21 study.centos.xiaoqi systemd[1]: Started Job spooling tools.
#重点在第二、三行~
#Loaded:这行在说明，开机的时候这个 unit 会不会启动，enabled 为开机启动，disabled 开机不会启动
#Active:现在这个 unit 的状态是正在执行 (running) 或没有执行 (dead)
#后面几行则是说明这个 unit 程序的 PID 状态以及最后一行显示这个服务的登录文件信息!
#登录文件信息格式为:『时间』『讯息发送主机』『哪一个服务的讯息』『实际讯息内容』
#所以上面的显示讯息是:这个 atd 预设开机就启动，而且现在正在运作的意思!


#范例二:正常关闭这个 atd 服务
[root@study Packages]# systemctl stop atd.service           
[root@study Packages]# systemctl status atd.service 
● atd.service - Job spooling tools
   Loaded: loaded (/usr/lib/systemd/system/atd.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since 一 2019-11-04 23:19:27 CST; 3s ago
  Process: 1537 ExecStart=/usr/sbin/atd -f $OPTS (code=exited, status=0/SUCCESS)
 Main PID: 1537 (code=exited, status=0/SUCCESS)

11月 04 19:00:21 study.centos.xiaoqi systemd[1]: Started Job spooling tools.
11月 04 23:19:27 study.centos.xiaoqi systemd[1]: Stopping Job spooling tools...
11月 04 23:19:27 study.centos.xiaoqi systemd[1]: Stopped Job spooling tools.
#目前这个 unit 下次开机还是会启动，但是现在是没在运作的状态中!同时，
#最后两行为新增加的登录讯息，告诉我们目前的系统状态喔!

#1.观察一下状态，确认是否为关闭/未启动呢?
[root@study Packages]# systemctl status chronyd.service 
● chronyd.service - NTP client/server
   Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled; vendor preset: enabled)
   Active: active (running) since 一 2019-11-04 19:00:43 CST; 4h 23min ago
  Process: 841 ExecStartPost=/usr/libexec/chrony-helper update-daemon (code=exited, status=0/SUCCESS)
  Process: 797 ExecStart=/usr/sbin/chronyd $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 811 (chronyd)
   CGroup: /system.slice/chronyd.service
           └─811 /usr/sbin/chronyd
......

#2.由上面知道目前是启动的，因此立刻将他关闭，同时开机不会启动才行!
[root@study Packages]# systemctl stop chronyd.service       
[root@study Packages]# systemctl disable chronyd.service       
Removed symlink /etc/systemd/system/multi-user.target.wants/chronyd.service.
#看得很清楚~其实就是从 /etc/systemd/system 底下删除一条连结文件而已~



[root@study Packages]# systemctl status chronyd.service 
● chronyd.service - NTP client/server
   Loaded: loaded (/usr/lib/systemd/system/chronyd.service; disabled; vendor preset: enabled)
   Active: inactive (dead)

#1.先看看 cups 的服务是开还是关?
[root@study Packages]# systemctl status cups.service 
● cups.service - CUPS Printing Service
   Loaded: loaded (/usr/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since 一 2019-11-04 19:00:20 CST; 4h 27min ago
 Main PID: 1525 (cupsd)
   CGroup: /system.slice/cups.service
           └─1525 /usr/sbin/cupsd -f
#有趣得很!竟然是 enable 但是却是 inactive 耶!相当特别!


#2.那就直接关闭，同时确认没有启动喔!
[root@study Packages]# systemctl stop cups.service 
Warning: Stopping cups.service, but it can still be activated by:
  cups.socket
  cups.path
[root@study Packages]# systemctl disable cups.service 
Removed symlink /etc/systemd/system/multi-user.target.wants/cups.path.
Removed symlink /etc/systemd/system/multi-user.target.wants/cups.service.
Removed symlink /etc/systemd/system/sockets.target.wants/cups.socket.
Removed symlink /etc/systemd/system/printer.target.wants/cups.service.
#也是非常特别!竟然一口气取消掉三个连结档!也就是说，这三个文件可能是有相依性的问题喔!


[root@study Packages]# netstat -luntp | grep cups
#现在应该不会出现任何数据!因为根本没有 cups 的任务在执行当中~所以不会有 port 产生


#尝试启动 cups.socket 监听客户端的需求喔!
[root@study Packages]# systemctl start cups.service 
[root@study Packages]# systemctl status cups.service cups.socket cups.path 
● cups.service - CUPS Printing Service
   Loaded: loaded (/usr/lib/systemd/system/cups.service; disabled; vendor preset: enabled)
   Active: inactive (dead) since 一 2019-11-04 23:31:12 CST; 26s ago
 Main PID: 9336 (cupsd)
   CGroup: /system.slice/cups.service
           └─9336 /usr/sbin/cupsd -f

11月 04 23:31:12 study.centos.xiaoqi systemd[1]: Started CUPS Printing Service.

● cups.socket - CUPS Printing Service Sockets
   Loaded: loaded (/usr/lib/systemd/system/cups.socket; disabled; vendor preset: enabled)
   Active: active (listening) since 一 2019-11-04 19:00:21 CST; 4h 31min ago
   Listen: /var/run/cups/cups.sock (Stream)

11月 04 19:00:21 study.centos.xiaoqi systemd[1]: Listening on CUPS Printing Service Sockets.

● cups.path - CUPS Printer Service Spool
   Loaded: loaded (/usr/lib/systemd/system/cups.path; disabled; vendor preset: enabled)
   Active: inactive (dead) since 一 2019-11-04 19:00:21 CST; 4h 31min ago
#确定仅有 cups.socket 在启动，其他的并没有启动的状态!


#4.尝试使用 lp 这个指令来打印看看?
[root@study Packages]# echo "testing" | lp
lp: Error - no default destination available. #实际上就是没有打印机!所以有错误也没关系!



[root@study Packages]# systemctl status cups.service 
● cups.service - CUPS Printing Service
   Loaded: loaded (/usr/lib/systemd/system/cups.service; disabled; vendor preset: enabled)
   Active: active (running) since 一 2019-11-04 23:31:12 CST; 4min 18s ago
 Main PID: 9336 (cupsd)
   CGroup: /system.slice/cups.service
           └─9336 /usr/sbin/cupsd -f
[root@study Packages]# netstat -luntp | grep cups
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      9336/cupsd          
tcp6       0      0 ::1:631                 :::*                    LISTEN      9336/cupsd  
#竟然 cups 自动被启动了!明明我们都没有驱动他啊!怎么回事啊?

#保持刚刚的状态，关闭 cups.service，启动 cups.socket，然后注销 cups.servcie
[root@study Packages]# systemctl stop cups.service 
Warning: Stopping cups.service, but it can still be activated by:
  cups.socket
  cups.path
[root@study Packages]# systemctl mask cups.service 
Created symlink from /etc/systemd/system/cups.service to /dev/null.
#其实这个 mask 注销的动作，只是让启动的脚本变成空的装置而已!


[root@study Packages]# systemctl status cups.service 
● cups.service
   Loaded: masked (/dev/null; bad)
   Active: inactive (dead) since 一 2019-11-04 23:37:27 CST; 51s ago
 Main PID: 9336 (code=exited, status=0/SUCCESS)


[root@study Packages]# systemctl start cups.service
Failed to start cups.service: Unit is masked.
#再也无法唤醒!

[root@study Packages]# systemctl unmask cups.service 
Removed symlink /etc/systemd/system/cups.service.
[root@study Packages]# systemctl status cups.service 
● cups.service - CUPS Printing Service
   Loaded: loaded (/usr/lib/systemd/system/cups.service; disabled; vendor preset: enabled)
   Active: inactive (dead) since 一 2019-11-04 23:37:27 CST; 2min 51s ago
 Main PID: 9336 (code=exited, status=0/SUCCESS)

[root@study ~]# systemctl [command] [--type=TYPE] [--all]
command:
    list-units :依据 unit 列出目前有启动的 unit。若加上 --all 才会列出没启动的。
    list-unit-files :依据 /usr/lib/systemd/system/ 内的文件，将所有文件列表说明。
--type=TYPE:就是之前提到的 unit type，主要有 service, socket, target 等


#范例一:列出系统上面有启动的 unit
[root@study ~]# systemctl
[root@i7dom ~]# systemctl
  UNIT                                                                                LOAD   ACTIVE SUB       DESCRIPTION
  proc-sys-fs-binfmt_misc.automount                                                   loaded active running   Arbitrary Executable File Formats File System Automount Point
  sys-devices-pci0000:00-0000:00:01.1-ata1-host0-target0:0:1-0:0:1:0-block-sr0.device loaded active plugged   QEMU_DVD-ROM config-2
  sys-devices-pci0000:00-0000:00:03.0-virtio0-net-eth0.device                         loaded active plugged   Virtio network device
  sys-devices-pci0000:00-0000:00:04.0-virtio1-block-vda-vda1.device                   loaded active plugged   /sys/devices/pci0000:00/0000:00:04.0/virtio1/block/vda/vda1
......
 vsftpd.service                               loaded active running   Vsftpd ftp daemon
......
 cups.path                                    loaded active waiting   CUPS Printer Service Spool

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.

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

#列出的项目中，主要的意义是:
#UNIT :项目的名称，包括各个 unit 的类别 (看扩展名)
#LOAD :开机时是否会被加载，默认 systemctl 显示的是有加载的项目而已喔!
#ACTIVE :目前的状态，须与后续的 SUB 搭配!就是我们用 systemctl status 观察时，active 的项目!
#DESCRIPTION :详细描述啰


#cups 比较有趣，因为刚刚被我们玩过，所以 ACTIVE 竟然是 failed 的喔!被玩死了!
#另外，systemctl 都不加参数，其实预设就是 list-units 的意思!



#范例二:列出所有已经安装的 unit 有哪些?
[root@study ~]# systemctl list-unit-files 
UNIT FILE                                     STATE   
proc-sys-fs-binfmt_misc.automount             static  
dev-hugepages.mount                           static  
dev-mqueue.mount                              static  
......
tmp.mount                                     disabled
var-lib-nfs-rpc_pipefs.mount                  static  
brandbot.path                                 disabled
cups.path                                     disabled
systemd-ask-password-console.path             static  
systemd-ask-password-plymouth.path            static  
systemd-ask-password-wall.path                static  
......
abrt-ccpp.service                             enabled 
abrt-oops.service                             enabled 
abrt-pstoreoops.service                       disabled
......
alsa-restore.service                          static  
alsa-state.service                            static  
alsa-store.service                            static  
 
372 unit files listed.

[root@study ~]# systemctl list-units --type=service --all 
  UNIT                                         LOAD      ACTIVE   SUB     DESCRIPTION
  abrt-ccpp.service                            loaded    active   exited  Install ABRT coredump hook
  abrt-oops.service                            loaded    active   running ABRT kernel log watcher
  abrt-vmcore.service                          loaded    inactive dead    Harvest vmcores for ABRT
  abrt-xorg.service                            loaded    active   running ABRT Xorg log watcher
  abrtd.service                                loaded    active   running ABRT Automated Bug Reporting Tool
  accounts-daemon.service                      loaded    active   running Accounts Service
  alsa-restore.service                         loaded    inactive dead    Restore Sound Card State
  alsa-state.service                           loaded    active   running Manage Sound Card State (restore and stor
  alsa-store.service                           loaded    inactive dead    Store Sound Card State
● apparmor.service                             not-found inactive dead    apparmor.service
#后缀为.service的项目会被输出


#范例一:查询系统上是否有以 cpu 为名的服务?
[root@study ~]# systemctl list-units --type=service --all | grep cpu
  cpupower.service                                      loaded    inactive dead    Configure CPU power related settings
#确实有喔!可以改变 CPU 电源管理机制的服务!

[root@study ~]# systemctl list-units --type=target --all
  UNIT                   LOAD      ACTIVE   SUB    DESCRIPTION
  basic.target           loaded    active   active Basic System
  cryptsetup.target      loaded    active   active Local Encrypted Volumes
  emergency.target       loaded    inactive dead   Emergency Mode
  final.target           loaded    inactive dead   Final Step
  getty-pre.target       loaded    inactive dead   Login Prompts (Pre)
  getty.target           loaded    active   active Login Prompts
  graphical.target       loaded    active   active 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    inactive dead   Network (Pre)
  network.target         loaded    active   active Network
  nfs-client.target      loaded    active   active NFS client services
  nss-lookup.target      loaded    inactive dead   Host and Network Name Lookups
  nss-user-lookup.target loaded    active   active User and Group Name Lookups
  paths.target           loaded    active   active Paths
  remote-fs-pre.target   loaded    active   active Remote File Systems (Pre)
  remote-fs.target       loaded    active   active Remote File Systems
  rescue.target          loaded    inactive dead   Rescue Mode
  rpcbind.target         loaded    inactive dead   RPC Port Mapper
  shutdown.target        loaded    inactive dead   Shutdown
  slices.target          loaded    active   active Slices
  sockets.target         loaded    active   active Sockets
  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.

30 loaded units listed.
To show all installed unit files use 'systemctl list-unit-files'.

[root@study ~]# systemctl [command] [unit.target]
选项与参数:
    get-default:取得目前的 target
    set-default:设定后面接的 target 成为默认的操作模式
    isolate:切换到后面接的模式


#范例一:我们的测试机器默认是图形界面，先观察是否真为图形模式，再将默认模式转为文字界面
[root@study ~]# systemctl get-default 
graphical.target #果然是图形界面喔!

[root@study ~]# systemctl set-default multi-user.target 
Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target.
[root@study ~]# systemctl get-default 
multi-user.target


#范例二:在不重新启动的情况下，将目前的操作环境改为纯文本模式，关掉图形界面
[root@study ~]# systemctl isolate multi-user.target 
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.
PolicyKit daemon reconnected to bus.
Attempting to re-register as an authentication agent.
We are now a registered authentication agent.
[root@study ~]# systemctl get-default 
multi-user.target


#范例三:若需要重新取得图形界面呢?
[root@study ~]# systemctl isolate graphical.target 
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.
PolicyKit daemon reconnected to bus.
Attempting to re-register as an authentication agent.

[root@study ~]# systemctl set-default graphical.target 
Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.
[root@study ~]# systemctl get-default 
graphical.target

[root@study ~]#systemctl poweroff    系统关机
[root@study ~]#systemctl reboot        系统重启
[root@study ~]#systemctl suspend    进入暂停模式
[root@study ~]#systemctl hibernate    进入休眠模式
[root@study ~]#systemctl rescue        强制进入救援模式
[root@study ~]#systemctl emergency    强制进入紧急救援模式

[root@study ~]# systemctl list-dependencies [unit] [--reverse]
选项与参数:
--reverse :反向追踪谁使用这个 unit 的意思!


#范例一:列出目前的 target 环境下，用到什么特别的 unit
[root@study ~]# systemctl get-default 
graphical.target

[root@study ~]# systemctl  list-dependencies 
default.target
● ├─accounts-daemon.service
● ├─gdm.service
● ├─network.service
● ├─rtkit-daemon.service
● ├─systemd-readahead-collect.service
● ├─systemd-readahead-replay.service
● ├─systemd-update-utmp-runlevel.service
● └─multi-user.target
●   ├─abrt-ccpp.service
●   ├─abrt-oops.service
●   ├─abrt-vmcore.service
......
●   ├─systemd-logind.service
●   ├─systemd-update-utmp-runlevel.service
●   ├─systemd-user-sessions.service
●   ├─tuned.service
●   ├─vmtoolsd.service
●   ├─vsftpd.service
●   ├─basic.target
●   │ ├─alsa-restore.service
●   │ ├─alsa-state.service
●   │ ├─firewalld.service
●   │ ├─microcode.service
●   │ ├─rhel-autorelabel-mark.service
●   │ ├─rhel-autorelabel.service
●   │ ├─rhel-configure.service
●   │ ├─rhel-dmesg.service
●   │ ├─rhel-loadmodules.service
●   │ ├─selinux-policy-migrate-local-changes@targeted.service
●   │ ├─paths.target
●   │ ├─slices.target
●   │ │ ├─-.slice
●   │ │ └─system.slice
●   │ ├─sockets.target
●   │ │ ├─avahi-daemon.socket
●   │ │ ├─dbus.socket
●   │ │ ├─dm-event.socket
●   │ │ ├─iscsid.socket
●   │ │ ├─iscsiuio.socket
●   │ │ ├─rpcbind.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
......
●   │ │
●   │ └─timers.target
●   │   └─systemd-tmpfiles-clean.timer
●   ├─getty.target
●   │ └─getty@tty1.service
●   ├─nfs-client.target
●   │ ├─auth-rpcgss-module.service
●   │ ├─rpc-statd-notify.service
●   │ └─remote-fs-pre.target
●   └─remote-fs.target
●     └─nfs-client.target
●       ├─auth-rpcgss-module.service
●       ├─rpc-statd-notify.service
●       └─remote-fs-pre.target

[root@study ~]# systemctl list-dependencies --reverse 
default.target
└─graphical.target

[root@study ~]# systemctl list-dependencies graphical.target 
graphical.target
● ├─accounts-daemon.service
● ├─gdm.service
● ├─network.service
● ├─rtkit-daemon.service
● ├─systemd-readahead-collect.service
● ├─systemd-readahead-replay.service
● ├─systemd-update-utmp-runlevel.service
● └─multi-user.target
●   ├─abrt-ccpp.service
●   ├─abrt-oops.service
●   ├─abrt-vmcore.service
●   ├─abrt-xorg.service
●   ├─abrtd.service
●   ├─atd.service
●   ├─auditd.service
●   ├─avahi-daemon.service
●   ├─brandbot.path
......

[root@study ~]# systemctl list-sockets 
LISTEN                         UNIT                         ACTIVATES
/dev/log                       systemd-journald.socket      systemd-journald.service
/run/dbus/system_bus_socket    dbus.socket                  dbus.service
/run/dmeventd-client           dm-event.socket              dm-event.service
/run/dmeventd-server           dm-event.socket              dm-event.service
/run/lvm/lvmetad.socket        lvm2-lvmetad.socket          lvm2-lvmetad.service
/run/lvm/lvmpolld.socket       lvm2-lvmpolld.socket         lvm2-lvmpolld.service
/run/systemd/initctl/fifo      systemd-initctl.socket       systemd-initctl.service
/run/systemd/journal/socket    systemd-journald.socket      systemd-journald.service
/run/systemd/journal/stdout    systemd-journald.socket      systemd-journald.service
/run/systemd/shutdownd         systemd-shutdownd.socket     systemd-shutdownd.service
/run/udev/control              systemd-udevd-control.socket systemd-udevd.service
/var/run/avahi-daemon/socket   avahi-daemon.socket          avahi-daemon.service
/var/run/rpcbind.sock          rpcbind.socket               rpcbind.service
@ISCSIADM_ABSTRACT_NAMESPACE   iscsid.socket                iscsid.service
@ISCSID_UIP_ABSTRACT_NAMESPACE iscsiuio.socket              iscsiuio.service
kobject-uevent 1               systemd-udevd-kernel.socket  systemd-udevd.service

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

[root@study ~]# cat /etc/services | grep -E '(ftp|http)' 
ftp             21/tcp
ftp             21/udp          fsp fspd
http            80/tcp          www www-http    # WorldWideWeb HTTP
http            80/udp          www www-http    # HyperText Transfer Protocol
http            80/sctp                         # HyperText Transfer Protocol
#这个文件的内容是以底下的方式来编排的:
#<daemon name>    <port/通讯协议>    <改服务的说明>

[root@study ~]# netstat -luntp 
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:555             0.0.0.0:*               LISTEN      1502/vsftpd         
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      4459/nginx: master  
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      2768/dnsmasq        
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1495/sshd           
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      2668/master         
tcp6       0      0 :::22                   :::*                    LISTEN      1495/sshd           
tcp6       0      0 ::1:25                  :::*                    LISTEN      2668/master         
udp        0      0 0.0.0.0:8067            0.0.0.0:*                           1302/dhclient       
udp        0      0 192.168.122.1:53        0.0.0.0:*                           2768/dnsmasq        
udp        0      0 0.0.0.0:67              0.0.0.0:*                           2768/dnsmasq        
udp        0      0 0.0.0.0:68              0.0.0.0:*                           1274/dhclient       
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           802/avahi-daemon: r 
udp        0      0 0.0.0.0:44452           0.0.0.0:*                           802/avahi-daemon: r 
udp        0      0 0.0.0.0:51680           0.0.0.0:*                           1274/dhclient       
udp6       0      0 :::28958                :::*                                1302/dhclient       
udp6       0      0 :::2393                 :::*                                1274/dhclient       
udp6       0      0 fe80::20c:29ff:fe61:546 :::*                                1302/dhclient 

[root@study ~]# systemctl list-units -all | grep avahi-daemon
  avahi-daemon.service                                                                                           loaded    active   running   Avahi mDNS/DNS-SD Stack
  avahi-daemon.socket                                                                                            loaded    active   running   Avahi mDNS/DNS-SD Stack Activation Socket

[root@study ~]# systemctl stop avahi-daemon.service 
Warning: Stopping avahi-daemon.service, but it can still be activated by:
  avahi-daemon.socket
  
[root@study ~]# systemctl stop avahi-daemon.socket 
[root@study ~]# systemctl disable avahi-daemon.service avahi-daemon.socket 
Removed symlink /etc/systemd/system/multi-user.target.wants/avahi-daemon.service.
Removed symlink /etc/systemd/system/sockets.target.wants/avahi-daemon.socket.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.Avahi.service.

[root@study ~]# netstat -luntp 
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:555             0.0.0.0:*               LISTEN      1502/vsftpd         
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      4459/nginx: master  
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      2768/dnsmasq        
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1495/sshd           
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      2668/master         
tcp6       0      0 :::22                   :::*                    LISTEN      1495/sshd           
tcp6       0      0 ::1:25                  :::*                    LISTEN      2668/master         
udp        0      0 0.0.0.0:8067            0.0.0.0:*                           1302/dhclient       
udp        0      0 192.168.122.1:53        0.0.0.0:*                           2768/dnsmasq        
udp        0      0 0.0.0.0:67              0.0.0.0:*                           2768/dnsmasq        
udp        0      0 0.0.0.0:68              0.0.0.0:*                           1274/dhclient       
udp        0      0 0.0.0.0:51680           0.0.0.0:*                           1274/dhclient       
udp6       0      0 :::28958                :::*                                1302/dhclient       
udp6       0      0 :::2393                 :::*                                1274/dhclient       
udp6       0      0 fe80::20c:29ff:fe61:546 :::*                                1302/dhclient 

[root@study ~]# cat -n /usr/lib/systemd/system/sshd.service 
     1  [Unit]    #这个项目与此 unit 的解释、执行服务相依性有关
     2  Description=OpenSSH server daemon
     3  Documentation=man:sshd(8) man:sshd_config(5)
     4  After=network.target sshd-keygen.service
     5  Wants=sshd-keygen.service
     6
     7  [Service]    #这个项目与实际执行的指令参数有关
     8  EnvironmentFile=/etc/sysconfig/sshd
     9  ExecStart=/usr/sbin/sshd -D $OPTIONS
    10  ExecReload=/bin/kill -HUP $MAINPID
    11  KillMode=process
    12  Restart=on-failure
    13  RestartSec=42s
    14
    15  [Install]    #这个项目说明此 unit 要挂载哪个 target 底下
    16  WantedBy=multi-user.target

#1.先建立好所需要的配置文件
[root@study ~]#cd /etc/vsftpd/
[root@study vsftpd]# cp vsftpd.conf vsftpd2.conf
▽root@study vsftpd]# vim vsftpd.conf 
#listen_port=555


[root@study vsftpd]# diff vsftpd.conf vsftpd2.conf 
129c129
< #listen_port=555
---
> listen_port=555
#注意这两个配置文件的差别喔!只有这一行不同而已!


#2.开始处理启动脚本设定
[root@study vsftpd]# cd /etc/systemd/system/
[root@study system]# cp /usr/lib/systemd/system/vsftpd.service vsftpd2.service
[root@study system]# vim vsftpd2.service 
[Unit]
Description=Vsftpd second ftp daemon  <--修改unit
After=network.target

[Service]
Type=forking
ExecStart=/usr/sbin/vsftpd /etc/vsftpd/vsftpd2.conf    <--配置文件

[Install]
WantedBy=multi-user.target
#重点在改了 vsftpd2.conf 这个配置文件喔!


#3.重载 systemd 的脚本配置文件内容
[root@study system]# systemctl daemon-reload 
[root@study system]# systemctl  list-unit-files --all | grep vsftp
vsftpd.service                                enabled 
vsftpd2.service                               disabled
vsftpd@.service                               disabled
vsftpd.target                                 disabled


[root@study system]# systemctl status vsftpd2.service 
● vsftpd2.service - Vsftpd second ftp daemon
   Loaded: loaded (/etc/systemd/system/vsftpd2.service; disabled; vendor preset: disabled)
   Active: inactive (dead)


[root@study system]# systemctl restart vsftpd.service vsftpd2.service 
[root@study system]# systemctl enable vsftpd.service vsftpd2.service        
Created symlink from /etc/systemd/system/multi-user.target.wants/vsftpd2.service to /etc/systemd/system/vsftpd2.service.
[root@study system]# systemctl status vsftpd.service vsftpd2.service       
● vsftpd.service - Vsftpd ftp daemon
   Loaded: loaded (/usr/lib/systemd/system/vsftpd.service; enabled; vendor preset: disabled)
   Active: active (running) since 三 2019-11-06 00:04:58 CST; 17s ago
 Main PID: 6745 (vsftpd)
   CGroup: /system.slice/vsftpd.service
           └─6745 /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf

11月 06 00:04:58 study.centos.xiaoqi systemd[1]: Stopped Vsftpd ftp daemon.
11月 06 00:04:58 study.centos.xiaoqi systemd[1]: Starting Vsftpd ftp daemon...
11月 06 00:04:58 study.centos.xiaoqi systemd[1]: Started Vsftpd ftp daemon.

● vsftpd2.service - Vsftpd second ftp daemon
   Loaded: loaded (/etc/systemd/system/vsftpd2.service; enabled; vendor preset: disabled)
   Active: active (running) since 三 2019-11-06 00:04:58 CST; 17s ago
 Main PID: 6747 (vsftpd)
   CGroup: /system.slice/vsftpd2.service
           └─6747 /usr/sbin/vsftpd /etc/vsftpd/vsftpd2.conf

11月 06 00:04:58 study.centos.xiaoqi systemd[1]: Starting Vsftpd second ftp daemon...
11月 06 00:04:58 study.centos.xiaoqi systemd[1]: Started Vsftpd second ftp daemon.


[root@study system]# netstat -luntp 
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:555             0.0.0.0:*               LISTEN      6747/vsftpd      <----555端口   
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      4459/nginx: master  
tcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN      6745/vsftpd      <----21端口
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      2768/dnsmasq        
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1495/sshd           
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      2668/master         
tcp6       0      0 :::22                   :::*                    LISTEN      1495/sshd   

[root@study ~]# cat //usr/lib/systemd/system/getty@.service 
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Getty on %I
Documentation=man:agetty(8) man:systemd-getty-generator(8)
Documentation=http://0pointer.de/blog/projects/serial-console.html
After=systemd-user-sessions.service plymouth-quit-wait.service getty-pre.target
After=rc-local.service

# If additional gettys are spawned during boot then we should make
# sure that this is synchronized before getty.target, even though
# getty.target didn't actually pull it in.
Before=getty.target
IgnoreOnIsolate=yes

# On systems without virtual consoles, don't start any getty. Note
# that serial gettys are covered by serial-getty@.service, not this
# unit.
ConditionPathExists=/dev/tty0

[Service]
# the VT is cleared by TTYVTDisallocate

ExecStart=-/sbin/agetty --noclear %I $TERM    

Type=idle
Restart=always
RestartSec=0
UtmpIdentifier=%I
TTYPath=/dev/%I
TTYReset=yes
TTYVHangup=yes
TTYVTDisallocate=yes
KillMode=process
IgnoreSIGPIPE=no
SendSIGHUP=yes

# Unset locale for the console getty since the console has problems
# displaying some internationalized messages.
Environment=LANG= LANGUAGE= LC_CTYPE= LC_NUMERIC= LC_TIME= LC_COLLATE= LC_MONETARY= LC_MESSAGES= LC_PAPER= LC_NAME= LC_ADDRESS= LC_TELEPHONE= LC_MEASUREMENT= LC_IDENTIFICATION=

[Install]

WantedBy=getty.target

DefaultInstance=tty1

[root@study ~]# systemctl show getty.target 
#那个 show 的指令可以将 getty.target 的默认设定值也取出来显示!
Names=getty.target
Wants=getty@tty1.service
WantedBy=multi-user.target
Conflicts=shutdown.target
Before=multi-user.target
After=getty@tty1.service getty@tty2.service getty@tty3.service getty@tty4.service
  getty@tty6.service getty@tty5.service

源文件:执行服务名称@.service 
执行文件:执行服务名称@范例名称.service

ExecStart=-/sbin/agetty --noclear %I $TERM

#1.修改预设的 logind.conf 内容，将原本 6 个虚拟终端机改成 4 个
[root@study ~]# vim /etc/systemd/logind.conf
[Login]
NAutoVTs=4
ReserveVT=0
#默认是6个且配置行被注释.


#关闭不小心启动的 tty5, tty6 并重新启动 getty.target!
[root@study ~]# systemctl stop getty@tty5.service
[root@study ~]# systemctl stop getty@tty6.service
[root@study ~]# systemctl restart systemd-logind.service

[root@study ~]# systemctl start getty@5.service

[root@study ~]# cat /usr/lib/systemd/system/vsftpd@.service 
[Unit]
Description=Vsftpd ftp daemon
After=network.target
PartOf=vsftpd.target

[Service]
Type=forking
ExecStart=/usr/sbin/vsftpd /etc/vsftpd/%i.conf

[Install]
WantedBy=vsftpd.target

#1.根据 vsftpd@.service 的建议，于 /etc/vsftpd/ 底下先建立新的配置文件
[root@study ~]# cd /etc/vsftpd/
[root@study vsftpd]# cp vsftpd.conf vsftpd3.conf
[root@study vsftpd]# vim vsftpd3.conf 
listen_port=2121  <--必须用listen_port


#2.暂时启动这个服务，不要永久启动他!
[root@study vsftpd]# systemctl start vsftpd@vsftpd3.service
[root@study vsftpd]# systemctl status vsftpd@vsftpd3.service 
vsftpd@vsftpd3.service - Vsftpd ftp daemon
Loaded: loaded (/usr/lib/systemd/system/vsftpd@.service; disabled) 
Active: active (running) since 六 2019-11-09 14:27:08 CST; 1min 33s ago

[root@study vsftpd]# netstat -luntp | grep 'vsftpd'
tcp        0      0 0.0.0.0:2121            0.0.0.0:*               LISTEN      28867/vsftpd        
tcp        0      0 0.0.0.0:555             0.0.0.0:*               LISTEN      27167/vsftpd        
tcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN      27643/vsftpd   

[root@study backups]# vim backup.sh 
#!/bin/bash

source="/etc /home /root /var/lib /var/spool/{cron,at,mail}"
target="/backups/backup-system-$(date +%y-%m-%d).tar.gz"
[ ! -d /backups  ] && mkdir /backups
tar -zcf ${target} ${source} &> /backups/backup.log


[root@study backups]# chmod a+x /backups/backup.sh 
[root@study backups]# ll
总用量 4
-rwxr-xr-x. 1 root root 220 11月  9 14:35 backup.sh
#记得要有可执行的权限才可以喔!

[root@study backups]# vim /etc/systemd/system/backup.service 

[Unit]
Description=backup my server
Requires=atd.service


[Service]
Type=simple
ExecStart=/bin/bash -c " echo /backups/backup.sh | at now"


[Install]
WantedBy=multi-user.target
#因为 ExecStart 里面有用到 at 这个指令，因此，atd.service 就是一定要的服务!

[root@study backups]# systemctl daemon-reload
[root@study backups]# systemctl start backup.service 
[root@study backups]# systemctl  status backup.service                                                             
● backup.service - backup my server
   Loaded: loaded (/etc/systemd/system/backup.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

11月 09 16:12:55 study.centos.xiaoqi systemd[1]: Started backup my server.
11月 09 16:12:55 study.centos.xiaoqi bash[31979]: job 9 at Sat Nov  9 16:12:00 2019
#为什么 Active 是 inactive 呢?这是因为我们的服务仅是一个简单的 script 啊!
#因此执行完毕就完毕了，不会继续存在内存中喔!

语法: 英文周名 YYYY-MM-DD HH:MM:SS 
范例: Thu     2015-08-13 13:40:00

隔3小时:            3h 或 3hr 或 3hours
隔30分钟过10秒:    10s300m
隔5天又100分钟:    100m5day
#通常英文的写法，小单位写前面，大单位写后面~所以先秒、再分、再小时、再天数等~

[root@study backups]# vim /etc/systemd/system/backup.timer

[Unit]
Description=backup my server timer

[Timer]
OnBootSec=2hrs
OnUnitActiveSec=2days

[Install]
WantedBy=multi-user.target
#只要这样设定就够了!保存离开!



[root@study backups]# systemctl daemon-reload 
[root@study backups]# systemctl enable backup.timer 
Created symlink from /etc/systemd/system/multi-user.target.wants/backup.timer to /etc/systemd/system/backup.timer.
[root@study backups]# systemctl restart backup.timer 
[root@study backups]# systemctl list-unit-files | grep 'backup'
backup.service                                disabled #个不需要启动!只要 enable backup.timer 即可!
backup.timer                                  enabled 


[root@study backups]# systemctl show time
ConditionTimestamp=五 2019-11-08 07:42:28 CST    # timer 这个 unit 启动的时间!


[root@study backups]# systemctl show backup.service
ExecMainExitTimestamp=五 2019-11-08 07:52:28 CST        # backup.service 上次执行的时间

[root@study ~]# systemctl show backup.timer 
NextElapseUSecMonotonic=2d 19min 11.540653s        # 下一次执行距离 timers.target 的时间

[root@study system]# vim /etc/systemd/system/backup2.timer 

[Unit]
Description=backup my server timer2


[Timer]
OnCalendar=Sun *-*-* 02:00:00
Persistent=true
Unit=backup.service

[Install]
WantedBy=multi-user.target


[root@study system]# systemctl daemon-reload 
[root@study system]# systemctl enable backup2.timer 
[root@study system]# systemctl start backup2.timer

[root@study system]# systemctl show backup2.timer 
NextElapseUSecRealtime=49y 10month 1w 1d 3h