RHCE——控制服务和守护进程

识别自动启动的系统进程

系统启动的服务器进程由systemd系统和服务器管理器进行管理
systemctl可以缩写或者省略单元名称、进度数条目和单元说明

• 服务单元具有.service扩展名，代表系统服务
• 套接字单元具有.socket扩展名，代表进程之间通信

• 路径单元具有.path扩展名，用于将服务的激活推迟到特定文件系统更改发生之后

  服务状态

[student@localhost 桌面]$ systemctl status sshdsshd.service - OpenSSH server daemon   Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)   Active: active (running) since 日 2017-07-30 22:38:24 CST; 2h 11min ago  Process: 6723 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS) Main PID: 6724 (sshd)   CGroup: /system.slice/sshd.service           └─6724 /usr/sbin/sshd -D

关键字 描述 loaded 单元配置文件已处理 active（tunning） 正通过一个或多个持续进程运行 active（exited） 已成功完成一次性配置 active（waiting） 运行中，但是在等待事件 inactive 不在运行 enable 将在系统启动时启动 disabled 不会iu在系统启动时启动 staic 无法启用，但是可以在某一启用单元自动启动

使用systemctl列出单元文件

1. 查询所有单元的状态，以验证系统启动

[student@localhost 桌面]$ systemctlUNIT                        LOAD   ACTIVE SUB       DESCRIPTIONproc-sys...t_misc.automount loaded active waiting   Arbitrary Executable File Fosys-devi...-sda-sda1.device loaded active plugged   VMware_Virtual_S...

1. 仅查询服务单元的状态

[student@localhost 桌面]$ systemctl --type=serviceUNIT                         LOAD   ACTIVE SUB     DESCRIPTIONabrt-ccpp.service            loaded active exited  Install ABRT coredump hookabrt-oops.service            loaded active running ABRT kernel log watcherabrt-xorg.service            loaded active running ABRT Xorg log watcher...

1. 查询处于失败或者维护的任何单元

[student@localhost 桌面]$ systemctl status rngd.service rngd.service - Hardware RNG Entropy Gatherer Daemon   Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled)   Active: active (running) since 日 2017-07-30 21:01:49 CST; 4h 14min ago Main PID: 911 (rngd)   CGroup: /system.slice/rngd.service           └─911 /sbin/rngd -f

1. 显示特定单元的活动和启用

[student@localhost 桌面]$ systemctl is-active sshdactive[student@localhost 桌面]$ systemctl is-enabled sshdenabled

1. 列出所有已加载单元的活动状态

[student@localhost 桌面]$ systemctl list-units --type=serviceUNIT                         LOAD   ACTIVE SUB     DESCRIPTIONabrt-ccpp.service            loaded active exited  Install ABRT coredump hookabrt-oops.service            loaded active running ABRT kernel log watcherabrt-xorg.service            loaded active running ABRT Xorg log watcher

1. 查看所有单元已启用和已禁用设置

[student@localhost 桌面]$ systemctl list-unit-files --type=serviceUNIT FILE                                   STATE   abrt-ccpp.service                           enabled abrt-oops.service                           enabled abrt-pstoreoops.service                     disabledabrt-vmcore.service                         enabled abrt-xorg.service                           enabled abrtd.service                               enabled accounts-daemon.service                     enabled alsa-restore.service                        static  ...

1. 仅查看失败的服务

[student@localhost 桌面]$ systemctl --failed --type=serviceUNIT          LOAD   ACTIVE SUB    DESCRIPTIONkdump.service loaded failed failed Crash recovery kernel armingrhnsd.service loaded failed failed LSB: Starts the Spacewalk DaemonLOAD   = 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.2 loaded units listed. Pass --all to see loaded but inactive units, too.To show all installed unit files use 'systemctl list-unit-files'.

控制系统服务

1.验证进程正在运行

[student@localhost 桌面]$ ps -up 6724USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMANDroot      6724  0.0  0.0  82956   104 ?        Ss   7月30   0:00 /usr/sbin/sshd

[student@localhost 桌面]$ ps auxUSER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMANDroot         1  0.0  0.5  53912  5672 ?        Ss   7月30   0:04 /usr/lib/systeroot         2  0.0  0.0      0     0 ?        S    7月30   0:00 [kthreadd]...

2.停止服务(注意权限问题)

[root@localhost ~]# systemctl stop sshd.service 

3.启动服务（进程ID已经改变）

[root@localhost ~]# systemctl start sshd.service 

4.重启服务

[root@localhost ~]# systemctl restart sshd.service 

5.重新加载配置文件（进程ID不变）

[root@localhost ~]# systemctl reload sshd.service

5.屏蔽服务

系统中装了相互冲突的服务
屏蔽将在配置目录中创建连接，使得启动服务时什么都不会发生

[root@localhost ~]# systemctl mask sshd.service ln -s '/dev/null' '/etc/systemd/system/sshd.service'[root@localhost ~]# systemctl unmask sshd.service rm '/etc/systemd/system/sshd.service'

使系统守护进程在系统启动时启动或停止

1.禁用服务，禁用服务并不会iu停止服务。

[root@localhost ~]# systemctl disable sshd.service rm '/etc/systemd/system/multi-user.target.wants/sshd.service'

2.启用服务

[root@localhost ~]# systemctl enable sshd.service ln -s '/usr/lib/systemd/system/sshd.service' '/etc/systemd/system/multi-user.target.wants/sshd.service'[root@localhost ~]# systemctl is-enabled sshd.service enabled

systemctl命令摘要

任务 命令 查看服务详细信息 systemctl status httpd.service 停止某服务 systemctl stop httpd.service 启动某服务 systemctl start httpd.service 重启某服务 systemctl restart httpd.service 重新加载服务配置 systemctl reload httpd.service 屏蔽服务 systemctl musk httpd.service 解除屏蔽 systemctl unmask http.service 使某服务自动启动 systemctl enable httpd.service 使某服务不自动启动 systemctl disable httpd.service 检查服务状态 systemctl is-active httpd.service （仅显示是否 Active) 显示所有已启动的服务 systemctl list-units –type=service