Linux centos7系统列出systemd下所有正在运行的服务

Linux系统提供各种系统服务(如进程管理、登录、syslog、cron等)和网络服务。
Linux支持不同的方法来管理服务(启动、停止、重启、在系统启动时的自动启动等)，通常通过流程或服务管理器。
大多数现代Linux发行版现在使用相同的进程管理器：systemd。

systemctl命令是管理systemd的主要工具

Systemd是Linux的系统和服务管理器; 
init进程的替代品，与SysV和LSB init脚本兼容。

systemctl将显示所有已加载的systemd单元

(有关systemd单元的更多信息，请阅读systemd文档)的列表，包括服务，并显示它们的状态(是否处于活动状态)

systemct

要列出系统上所有已加载的服务（无论是活动的，运行的，退出的还是失败的，请使用 list-units子命令和--type开关，其值为service。

//键入systemctl -- ##补充tab键就会出现下面的参数列表
[root@etcd2 conf]# systemctl -- 
--after                --full                 --no-block             --quiet                --system
--all                  --global               --no-legend            --recursive            --type
--before               --help                 --no-pager             --reverse              --version
--defaults             --host                 --no-reload            --root                 
--fail                 --ignore-dependencies  --no-wall              --runtime              
--failed               --kill-who             --privileged           --signal               
--force                --no-ask-password      --property             --state                
[root@etcd2 conf]# systemctl -- 
--after                --full                 --no-block             --quiet                --system
--all                  --global               --no-legend            --recursive            --type
--before               --help                 --no-pager             --reverse              --version
--defaults             --host                 --no-reload            --root                 
--fail                 --ignore-dependencies  --no-wall              --runtime              
--failed               --kill-who             --privileged           --signal               
--force                --no-ask-password      --property             --state     

//tab键补全就会显示下面的命令列表

[root@etcd2 conf]# systemctl list-
list-dependencies list-jobs list-sockets list-timers list-unit-files list-units

[root@etcd2 conf]# systemctl --version
systemd 219
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN

[root@ht8 ~]# systemctl list-units --type=service
  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
  abrtd.service                          loaded active running ABRT Automated Bug Reporting Tool
  atd.service                            loaded active running Job spooling tools
  auditd.service                         loaded active running Security Auditing Service
  calico-node.service                    loaded active running calico node
● cloud-set-guest-password.service       loaded failed failed  SYSV: Password Download Client
  crond.service                          loaded active running Command Scheduler
  dbus.service                           loaded active running D-Bus System Message Bus
  docker.service                         loaded active running Docker Application Container Engine
  getty@tty1.service                     loaded active running Getty on tty1
  gssproxy.service                       loaded active running GSSAPI Proxy Daemon
  irqbalance.service                     loaded active running irqbalance daemon
  kmod-static-nodes.service              loaded active exited  Create list of required static device nodes for the current kernel
  kube-proxy.service                     loaded active running Kubernetes Kube-Proxy Server
  kubelet.service                        loaded active running Kubernetes Kubelet Server
  libstoragemgmt.service                 loaded active running libstoragemgmt plug-in server daemon
  lvm2-lvmetad.service                   loaded active running LVM2 metadata daemon
  lvm2-monitor.service                   loaded active exited  Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress p
  lvm2-pvscan@8:0.service                loaded active exited  LVM2 PV scan on device 8:0
  lvm2-pvscan@8:18.service               loaded active exited  LVM2 PV scan on device 8:18
  network.service                        loaded active exited  LSB: Bring up/down networking
  NetworkManager-wait-online.service     loaded active exited  Network Manager Wait Online
  NetworkManager.service                 loaded active running Network Manager

或者

[root@ht8 ~]# systemctl --type=service
  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
  abrtd.service                          loaded active running ABRT Automated Bug Reporting Tool
  atd.service                            loaded active running Job spooling tools
  auditd.service                         loaded active running Security Auditing Service
  calico-node.service                    loaded active running calico node
● cloud-set-guest-password.service       loaded failed failed  SYSV: Password Download Client
  crond.service                          loaded active running Command Scheduler
  dbus.service                           loaded active running D-Bus System Message Bus
  docker.service                         loaded active running Docker Application Container Engine
  getty@tty1.service                     loaded active running Getty on tty1
  gssproxy.service                       loaded active running GSSAPI Proxy Daemon
  irqbalance.service                     loaded active running irqbalance daemon
  kmod-static-nodes.service              loaded active exited  Create list of required static device nodes for the current kernel
  kube-proxy.service                     loaded active running Kubernetes Kube-Proxy Server
  kubelet.service                        loaded active running Kubernetes Kubelet Server
  libstoragemgmt.service                 loaded active running libstoragemgmt plug-in server daemon
  lvm2-lvmetad.service                   loaded active running LVM2 metadata daemon
  lvm2-monitor.service                   loaded active exited  Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress p
  lvm2-pvscan@8:0.service                loaded active exited  LVM2 PV scan on device 8:0
  lvm2-pvscan@8:18.service               loaded active exited  LVM2 PV scan on device 8:18
  network.service                        loaded active exited  LSB: Bring up/down networking
  NetworkManager-wait-online.service     loaded active exited  Network Manager Wait Online
  NetworkManager.service                 loaded active running Network Manager
lines 1-25

 

要列出所有已加载但处于活动状态的服务，包括正在运行的服务和已退出的服务，可以添加--state选项，其值为active，如下所示。

  

[root@ht8 ~]# systemctl list-units --type=service --state=active
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
abrtd.service                          loaded active running ABRT Automated Bug Reporting Tool
atd.service                            loaded active running Job spooling tools
auditd.service                         loaded active running Security Auditing Service
calico-node.service                    loaded active running calico node
crond.service                          loaded active running Command Scheduler
dbus.service                           loaded active running D-Bus System Message Bus
docker.service                         loaded active running Docker Application Container Engine
getty@tty1.service                     loaded active running Getty on tty1
gssproxy.service                       loaded active running GSSAPI Proxy Daemon
irqbalance.service                     loaded active running irqbalance daemon
kmod-static-nodes.service              loaded active exited  Create list of required static device nodes for the current kernel
kube-proxy.service                     loaded active running Kubernetes Kube-Proxy Server
kubelet.service                        loaded active running Kubernetes Kubelet Server
libstoragemgmt.service                 loaded active running libstoragemgmt plug-in server daemon
lvm2-lvmetad.service                   loaded active running LVM2 metadata daemon
lvm2-monitor.service                   loaded active exited  Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress pol
lvm2-pvscan@8:0.service                loaded active exited  LVM2 PV scan on device 8:0
lvm2-pvscan@8:18.service               loaded active exited  LVM2 PV scan on device 8:18
network.service                        loaded active exited  LSB: Bring up/down networking
NetworkManager-wait-online.service     loaded active exited  Network Manager Wait Online
NetworkManager.service                 loaded active running Network Manager
nginx-proxy.service                    loaded active running kubernetes apiserver docker wrapper
lines 1-25

 

如果要快速浏览所有正在运行的服务（即所有已加载和正在运行的服务），请运行以下命令。

systemctl命令                  说明
systemctl                     列出所有的系统服务
[root@etcd2 system]#  systemctl
  UNIT                                                  LOAD   ACTIVE SUB       DESCRIPTION
  proc-sys-fs-binfmt_misc.automount                     loaded active waiting   Arbitrary Executable File Formats File System Automoun
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:0-0:0:0:0-block-sr0.device loaded active plugged   VMware_Virtual_IDE_CDROM
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:1-0:0:1:0-block-sda-sda1.device loaded active plugged   VMware_Virtual_IDE_
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:1-0:0:1:0-block-sda-sda2.device loaded active plugged   LVM PV dJcKYm-10WN-
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:1-0:0:1:0-block-sda.device loaded active plugged   VMware_Virtual_IDE_Hard_
  sys-devices-pci0000:00-0000:00:15.0-0000:03:00.0-host2-port\x2d2:0-end_device\x2d2:0-target2:0:0-2:0:0:0-block-sdb.device loaded act
....
  //列出所有启动unit
 [root@etcd2 system]# systemctl list-units
  UNIT                                                  LOAD   ACTIVE SUB       DESCRIPTION
  proc-sys-fs-binfmt_misc.automount                     loaded active waiting   Arbitrary Executable File Formats File System Automoun
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:0-0:0:0:0-block-sr0.device loaded active plugged   VMware_Virtual_IDE_CDROM
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:1-0:0:1:0-block-sda-sda1.device loaded active plugged   VMware_Virtual_IDE_
  sys-devices-pci0000:00-0000:00:07.1-ata1-host0-target0:0:1-0:0:1:0-block-sda-sda2.device loaded active plugged   LVM PV dJcKYm-10WN-
.....
 //列出所有启动文件
[root@etcd2 system]# 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
systemd-ask-password-console.path             static  
systemd-ask-password-plymouth.path            static  
systemd-ask-password-wall.path                static  
session-153.scope                             static  
...
// 列出所有service类型的unit

[root@etcd2 system]# 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    inactive dead    ABRT Xorg log watcher
  abrtd.service                                         loaded    active   running ABRT Automated Bug Reporting Tool
  atd.service                                           loaded    active   running Job spooling tools
  auditd.service                                        loaded    active   running Security Auditing Service
  auth-rpcgss-module.service                            loaded    inactive dead    Kernel Module supporting RPCSEC_GSS
  brandbot.service                                      loaded    inactive dead    Flexible Branding Service
  calico-node.service                                   loaded    active   running calico node
● cloud-set-guest-password.service                      loaded    failed   failed  SYSV: Password Download Client
...
//列出 kube-proxy的服务
[root@etcd2 system]# systemctl list-units --type=service --all | grep kube-proxy  
  kube-proxy.service                                    loaded    active   running Kubernetes Kube-Proxy Server

//列出所有target
[root@etcd2 system]# systemctl list-units --type=target --all  
  UNIT                   LOAD      ACTIVE   SUB    DESCRIPTION
  basic.target           loaded    active   active Basic System
  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
....


[root@etcd2 system]# 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    inactive dead    ABRT Xorg log watcher
  abrtd.service                                         loaded    active   running ABRT Automated Bug Reporting Tool
  atd.service                                           loaded    active   running Job spooling tools

[root@ht8 ~]# systemctl list-units --type=service --state=running
UNIT                     LOAD   ACTIVE SUB     DESCRIPTION
abrt-oops.service        loaded active running ABRT kernel log watcher
abrtd.service            loaded active running ABRT Automated Bug Reporting Tool
atd.service              loaded active running Job spooling tools
auditd.service           loaded active running Security Auditing Service
calico-node.service      loaded active running calico node
crond.service            loaded active running Command Scheduler
dbus.service             loaded active running D-Bus System Message Bus
docker.service           loaded active running Docker Application Container Engine
getty@tty1.service       loaded active running Getty on tty1
gssproxy.service         loaded active running GSSAPI Proxy Daemon
irqbalance.service       loaded active running irqbalance daemon
kube-proxy.service       loaded active running Kubernetes Kube-Proxy Server
kubelet.service          loaded active running Kubernetes Kubelet Server
libstoragemgmt.service   loaded active running libstoragemgmt plug-in server daemon
lvm2-lvmetad.service     loaded active running LVM2 metadata daemon
NetworkManager.service   loaded active running Network Manager
nginx-proxy.service      loaded active running kubernetes apiserver docker wrapper
ntpd.service             loaded active running Network Time Service
polkit.service           loaded active running Authorization Manager
postfix.service          loaded active running Postfix Mail Transport Agent
rngd.service             loaded active running Hardware RNG Entropy Gatherer Daemon
rpcbind.service          loaded active running RPC bind service
rsyslog.service          loaded active running System Logging Service                                                                                                                                                    loaded active running   Network Time Service

 

一、service常用管理,kube-proxy服务为例

k8s注册到系统的服务一般有
kube-apiserver.service
kube-controller-manager.service
kubelet.service
kube-proxy.service
kube-scheduler.service
nginx-proxy.service
//cni网络
calico-node.service
//引擎
docker.service 
//时间对于很多应用，例如：打卡，社交等必须的
ntpd.service
ntpdate.service
下面是常用操作
// 开机启动
[root@ht23 net.d]#systemctl enable kube-proxy.service
//关闭开机启动
[root@ht23 net.d]#systemctl disable kube-proxy.service
//启动服务
[root@ht23 net.d]#systemctl start kube-proxy.service
//停止服务
[root@ht23 net.d]#systemctl stop kube-proxy.service
// 重启服务
[root@ht23 net.d]#systemctl restart kube-proxy.service

//查看服务状态

[root@ht23 net.d]# systemctl status kube-proxy.service

//查看服务是否激活状态
[root@ht23 net.d]#systemctl is-active kube-proxy.service
active
//查看是否开机启动
[root@ht23 net.d]#systemctl is-enabled kube-proxy.service
enabled
//杀死服务进程
systemctl kill kube-proxy.service

 

二、服务启动的配置文件，下面以自建的kube-proxy.service为例

配置文件主要都放在 /usr/lib/systemd/system 或/lib/systemd/system 目录.

[root@ht23 k8snode]# ls   /usr/lib/systemd/system
abrt-ccpp.service                       lvm2-lvmpolld.service               runlevel2.target
abrtd.service                           lvm2-lvmpolld.socket                runlevel2.target.wants
abrt-oops.service                       lvm2-monitor.service                runlevel3.target
abrt-pstoreoops.service                 lvm2-pvscan@.service                runlevel3.target.wants
abrt-vmcore.service                     machine.slice                       runlevel4.target
abrt-xorg.service                       machines.target                     runlevel4.target.wants
arp-ethers.service                      mdadm-grow-continue@.service        runlevel5.target
......

kube-proxy.service配置文件举例：

# 查看 kube-proxy.service 服务对应的启动配置文件

[root@ht23 net.d]# systemctl cat kube-proxy.service
# /usr/lib/systemd/system/kube-proxy.service
[Unit]
Description=Kubernetes Kube-Proxy Server
Documentation=https://github.com/GoogleCloudPlatform/kubernetes
After=network.target

[Service]
EnvironmentFile=-/etc/kubernetes/conf/config
EnvironmentFile=-/etc/kubernetes/conf/proxy
ExecStart=/usr/local/bin/hyperkube proxy \
$KUBE_LOGTOSTDERR \
$KUBE_LOG_LEVEL \
$KUBE_MASTER \
$KUBE_PROXY_ARGS
Restart=on-failure
LimitNOFILE=65536

[Install]
WantedBy=multi-user.target //WantedBy：表示该服务所在的 Target(服务组)

 

//保存后
 cp 文件--->/usr/lib/systemd/system 或/lib/systemd/system下
systemctl daemon-reload //重载配置文件

 Service启动配置文件讲解

EnvironmentFile：许多软件都有自己的环境参数文件，该字段指定文件路径
注意：/etc/profile 或者 /etc/profile.d/ 这些文件中配置的环境变量仅对通过 pam 登录的用户生效，而 systemd 是不读这些配置的。
systemd 是所有进程的父进程或祖先进程，它的环境变量会被所有的子进程所继承，如果需要给 systemd 配置默认参数可以在 /etc/systemd/system.conf  和 /etc/systemd/user.conf 中设置。
加载优先级 system.conf 最低，可能会被其他的覆盖。

Type：定义启动类型。可设置：simple，exec，forking，oneshot，dbus，notify，idle
simple(设置了 ExecStart= 但未设置 BusName= 时的默认值)：ExecStart 字段启动的进程为该服务的主进程
forking：ExecStart 字段的命令将以 fork() 方式启动，此时父进程将会退出，子进程将成为主进程

ExecStart：定义启动进程时执行的命令
上面的例子中，启动 sshd 执行的命令是 /usr/sbin/sshd -D $OPTIONS，其中的变量 $OPTIONS 就来自 EnvironmentFile 字段指定的环境参数文件。类似的，还有如下字段：
ExecReload：   重启服务时执行的命令
ExecStop：     停止服务时执行的命令
ExecStartPre： 启动服务之前执行的命令
ExecStartPost：启动服务之后执行的命令
ExecStopPost： 停止服务之后执行的命令
RemainAfterExit：设为yes，表示进程退出以后，服务仍然保持执行
KillMode：定义 Systemd 如何停止服务，可以设置的值如下：
control-group（默认值）：当前控制组里面的所有子进程，都会被杀掉
process：只杀主进程
mixed：主进程将收到 SIGTERM 信号，子进程收到 SIGKILL 信号
none：没有进程会被杀掉，只是执行服务的 stop 命令
Restart：定义了退出后，Systemd 的重启方式。可以设置的值如下：
no（默认值）：退出后不会重启
on-success：只有正常退出时（退出状态码为0），才会重启
on-failure：非正常退出时（退出状态码非0），包括被信号终止和超时，才会重启
on-abnormal：只有被信号终止和超时，才会重启
on-abort：只有在收到没有捕捉到的信号终止时，才会重启
on-watchdog：超时退出，才会重启
always：不管是什么退出原因，总是重启
RestartSec：表示 Systemd 重启服务之前，需要等待的秒数

 

关于 Target，运行级别

# 查看默认 Target

   [root@etcd2 system]# systemctl get-default
   multi-user.target

 multi-user.target表示默认的启动Target是multi-user.target。在这个组里的所有服务，都将开机启动。这就是为什么 systemctl enable 命令能设置开机启动的原因

# 查看 multi-user.target 包含的所有服务

[root@etcd2 system]# systemctl list-dependencies multi-user.target
 multi-user.target
 ● ├─abrt-ccpp.service
 ● ├─abrt-oops.service
 ● ├─abrt-vmcore.service
 ● ├─abrt-xorg.service
 ● ├─abrtd.service
 ● ├─atd.service
 ● ├─auditd.service
 ● ├─brandbot.path
 ● ├─calico-node.service
 ● ├─cloud-set-guest-password.service
 ● ├─crond.service
 ● ├─dbus.service
 ● ├─docker.service
 ● ├─etcd.service
 ● ├─irqbalance.service
 ● ├─kube-apiserver.service
 ......

# shutdown.target表示关机状态的

[root@etcd2 system]# systemctl list-dependencies shutdown.target
shutdown.target
● └─dracut-shutdown.service

# 常用的 Target 有两个：一个是 multi-user.target，表示多用户命令行状态；另一个是 graphical.target，表示图形用户状态，

[root@etcd2 system]# systemctl list-dependencies graphical.target //它依赖于 multi-user.target

graphical.target

● ├─cloud-set-guest-password.service
● ├─display-manager.service
● ├─network.service
● ├─systemd-update-utmp-runlevel.service
● ├─vmware-tools.service
● └─multi-user.target
● ├─abrt-ccpp.service
● ├─abrt-oops.service
● ├─abrt-vmcore.service
● ├─abrt-xorg.service
● ├─abrtd.service
● ├─atd.service
● ├─auditd.service
● ├─brandbot.path
● ├─calico-node.service
● ├─cloud-set-guest-password.service
● ├─crond.service
● ├─dbus.service
● ├─docker.service
● ├─etcd.service
● ├─irqbalance.service
● ├─kube-apiserver.service
● ├─kube-controller-manager.service
● ├─kube-proxy.service
.....

[root@etcd2 system]# systemctl status shutdown.target
● shutdown.target - Shutdown
Loaded: loaded (/usr/lib/systemd/system/shutdown.target; static; vendor preset: disabled)
Active: inactive (dead)
Docs: man:systemd.special(7)

  这里补充下Linux下的7个运行级别：

0:系统停机状态，系统默认运行级别不能设置为0，否则不能正常启动，机器关闭。
1:单用户工作状态，root权限，用于系统维护，禁止远程登陆，就像Windows下的安全模式登录。
2:多用户状态，没有NFS支持。
3:完整的多用户模式，有NFS，登陆后进入控制台命令行模式。
4:系统未使用，保留一般不用，在一些特殊情况下可以用它来做一些事情。例如在笔记本电脑的电池用尽时，可以切换到这个模式来做一些设置。
5:X11控制台，登陆后进入图形GUI模式，XWindow系统。
6:系统正常关闭并重启，默认运行级别不能设为6，否则不能正常启动。运行init6机器就会重启。

  标准的Linux运行级别为3或5

  运行级别原理：

1.在目录/etc/rc.d/init.d下有许多服务器脚本程序，一般称为服务(service)
2.在/etc/rc.d下有9个文件，rc{n}.d对应系统的7个运行级别

   [root@etcd2 system]# cat /etc/rc.d/
   init.d/ rc0.d/ rc1.d/ rc2.d/ rc3.d/ rc4.d/ rc5.d/ rc6.d/ rc.local

3.rc{n}.d目录下都是一些符号链接文件，这些链接文件都指向init.d目录下的service脚本文件，命名规则为K+nn+服务名或S+nn+服务名，其中nn为两位数字。
4.系统会根据指定的运行级别进入对应的rcN.d目录，并按照文件名顺序检索目录下的链接文件：对于以K(Kill)开头的文件，系统将终止对应的服；对于以S(Start)开头的文件，系统将启动对应的服务
5.查看运行级别用：runlevel
6.进入其它运行级别用：initN，如果init3则进入终端模式，init5则又登录图形GUI模式
7.另外init0为关机，init6为重启系统

   标准的Linux运行级别为3或5，如果是3的话，系统就在多用户状态；如果是5的话，则是运行着XWindow系统。不同的运行级别有不同的用处，也应该根据自己的不同情形来设置。例如，如果丢失了root口令，那么可以让机器启动进入单用户状态来设置。在启动后的lilo提示符下输入： init=/bin/shrw

   这样就可以使机器进入运行级别1，并把root文件系统挂为读写。它会路过所有系统认证，让你使用passwd程序来改变root口令，然后启动到一个新的运行级。

建完配置文件设置自启动

# 添加或修改配置文件后，需要重新加载
systemctl daemon-reload

# 设置自启动，实质就是在 /etc/systemd/system/multi-user.target.wants/ 添加服务文件的链接
systemctl enable zdy

  其他请查看官方手册 https://www.freedesktop.org/software/systemd/man/systemd.service.html