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📜  系统服务启动和停止

📅  最后修改于: 2020-10-31 13:19:14             🧑  作者: Mango

systemd是在Linux上运行服务的新方式。 systemd具有取代的sysvinit 。 systemd为Linux带来了更快的启动时间，现在已成为管理Linux服务的标准方法。虽然稳定，但systemd仍在发展。

systemd作为一个初始化系统，用于管理引导Linux内核后需要更改状态的服务和守护程序。通过状态更改，可以应用启动，停止，重新加载和调整服务状态。

首先，让我们检查当前在服务器上运行的systemd的版本。

[centos@localhost ~]$ systemctl --version 
systemd 219 
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP 
+GCRYPT +GNUTLS +ACL     +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN

[centos@localhost ~]$

从CentOS版本7开始，在撰写本文时已完全更新，系统版本219是当前的稳定版本。

我们还可以使用systemd-analyze分析上次服务器启动时间

[centos@localhost ~]$ systemd-analyze    
Startup finished in 1.580s (kernel) + 908ms (initrd) + 53.225s (userspace) = 55.713s 
[centos@localhost ~]$

当系统启动时间较慢时，我们可以使用systemd-analyze blame命令。

[centos@localhost ~]$ systemd-analyze blame 
   40.882s kdump.service 
   5.775s NetworkManager-wait-online.service 
   4.701s plymouth-quit-wait.service 
   3.586s postfix.service 
   3.121s systemd-udev-settle.service 
   2.649s tuned.service 
   1.848s libvirtd.service 
   1.437s network.service 
   875ms packagekit.service 
   855ms gdm.service 
   514ms firewalld.service 
   438ms rsyslog.service
   436ms udisks2.service 
   398ms sshd.service 
   360ms boot.mount 
   336ms polkit.service 
   321ms accounts-daemon.service

使用systemd时，了解单位的概念很重要。单位是系统知道如何解释的资源。单位分为以下12种类型-

  • 。服务
  • 。插座
  • 。设备
  • 。安装
  • .automount
  • 。交换
  • 。目标
  • 。路径
  • .timer
  • .snapshot
  • 。片
  • 。范围

在大多数情况下，我们将使用.service作为目标单元。建议对其他类型进行进一步研究。因为只有.service单位才适用于启动和停止systemd服务。

每个单元均在位于以下位置的文件中定义-

  • / lib / systemd / system-基本单元文件

  • / etc / systemd / system-修改后的单位文件在运行时启动

使用systemctl管理服务

要使用systemd ，我们需要非常熟悉systemctl命令。以下是systemctl最常用的命令行开关。

Switch Action
-t Comma separated value of unit types such as service or socket
-a Shows all loaded units
–state Shows all units in a defined state, either: load, sub, active, inactive, etc..
-H Executes operation remotely. Specify Host name or host and user separated by @.

系统基本用法

systemctl [operation]
example: systemctl --state [servicename.service]

快速浏览一下我们包装盒上运行的所有服务。

[root@localhost rdc]# systemctl -t 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 
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-state.service         loaded   active   running    Manage Sound Card State (restore and store) 
atd.service                loaded   active   running    Job spooling tools 
auditd.service             loaded   active   running    Security Auditing Service 
avahi-daemon.service       loaded   active   running    Avahi mDNS/DNS-SD Stack 
blk-availability.service   loaded   active   exited     Availability of block devices 
bluetooth.service          loaded   active   running    Bluetooth service 
chronyd.service            loaded   active   running    NTP client/server

停止服务

首先，停止蓝牙服务。

[root@localhost]# systemctl stop bluetooth

[root@localhost]# systemctl --all -t service | grep bluetooth      
bluetooth.service   loaded    inactive dead    Bluetooth service

[root@localhost]#

如我们所见，蓝牙服务现在处于非活动状态。

重新启动蓝牙服务。

[root@localhost]# systemctl start bluetooth

[root@localhost]# systemctl --all -t service | grep bluetooth 
bluetooth.service  loaded    active   running Bluetooth     service

[root@localhost]#

注意-我们没有指定bluetooth.service，因为隐含.service 。最好考虑将单元类型附加到我们要处理的服务中。因此，从这里开始，我们将使用.service扩展名来阐明我们正在处理服务单元操作。

可以对服务执行的主要操作是-

Start Starts the service
Stop Stops a service
Reload Reloads the active configuration of a service w/o stopping it (like kill -HUP in system v init)
Restart Starts, then stops a service
Enable Starts a service at boot time
Disable Stops a service from automatically starting at run time

以上操作主要用于以下情况-

Start To bring a service up that has been put in the stopped state.
Stop To temporarily shut down a service (for example when a service must be stopped to access files locked by the service, as when upgrading the service)
Reload When a configuration file has been edited and we want to apply the new changes while not stopping the service.
Restart In the same scenario as reload, but the service does not support reload.
Enable When we want a disabled service to run at boot time.
Disable Used primarily when there is a need to stop a service, but it starts on boot.

检查服务状态-

[root@localhost]# systemctl status network.service 
network.service - LSB: Bring up/down networking 
Loaded: loaded (/etc/rc.d/init.d/network; bad; vendor preset: disabled) 
Active: active (exited) since Sat 2017-01-14 04:43:48 EST; 1min 31s ago 
Docs: man:systemd-sysv-generator(8)

Process: 923 ExecStart = /etc/rc.d/init.d/network start (code=exited, status = 0/SUCCESS)

localhost.localdomain systemd[1]: Starting LSB: Bring up/down networking... 
localhost.localdomain network[923]: Bringing up loopback interface:  [  OK  ] 
localhost.localdomain systemd[1]: Started LSB: Bring up/down networking.

[root@localhost]#

向我们显示网络服务的当前状态。如果我们想查看所有与网络相关的服务，我们可以使用-

[root@localhost]# systemctl --all -t service | grep -i network 
network.service                       loaded    active    exited    LSB: Bring up/ 
NetworkManager-wait-online.service    loaded    active    exited    Network Manager  
NetworkManager.service                loaded    active    running   Network Manager 
ntpd.service                          loaded    inactive  dead      Network Time  
rhel-import-state.service             loaded    active    exited    Import network      

[root@localhost]#

对于那些熟悉sysinit管理服务方法的人，重要的是过渡到systemd 。 systemd是在Linux中启动和停止守护程序服务的新方法。