Systemctl命令

systemctl命令Systemd是一个系统管理守护进程、工具和库的集合，用于取代System 初始进程。Systemd的功能是用于集中管理和配置类UNIX系统

1. 首先检查你的系统中是否安装有systemd并确定当前安装的版本

    # systemctl --version
    systemd 215
    +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR

2. 检查systemd和systemctl的二进制文件和库文件的安装位置

    # whereis systemd 
    systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
    # whereis systemctl
    systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz

3. 检查systemd是否运行

    # ps -eaf | grep [s]ystemd
    root         1     0  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd --switched-root --system 
    --deserialize 23
    root       444     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-journald
    root       469     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-udevd
    root       555     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-logind
    dbus       556     1  0 16:27 ?        00:00:00 /bin/dbus-daemon --system --address=systemd: --
    nofork --nopidfile --systemd-activation

4. 分析systemd启动进程

    # systemd-analyze
    Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s

5. 分析启动时各个进程花费的时间

    # systemd-analyze blame
    8.565s mariadb.service
    7.991s webmin.service
    6.095s postfix.service
    4.311s httpd.service
    3.926s firewalld.service
    3.780s kdump.service
    3.238s tuned.service
    1.712s network.service
    1.394s lvm2-monitor.service
    1.126s systemd-logind.service

6. 分析启动时的关键链

    # systemd-analyze critical-chain
    The time after the unit is active or started is printed after the "@" character.
    The time the unit takes to start is printed after the "+" character.
    multi-user.target @20.222s
    └─mariadb.service @11.657s +8.565s

7. 列出所有可用单元

    # systemctl list-unit-files
    UNIT file                                   STATE   
    proc-sys-fs-binfmt_misc.automount           static  
    dev-hugepages.mount                         static  
    dev-mqueue.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
    brandbot.path                               disabled

8. 列出所有服务（包括启用的和禁用的）

    # systemctl list-unit-files --type=service
    UNIT FILE                                   STATE   
    arp-ethers.service                          disabled
    auditd.service                              enabled 
    autovt@.service                             disabled
    blk-availability.service                    disabled
    brandbot.service                            static  
    collectd.service                            disabled
    console-getty.service                       disabled
    console-shell.service                       disabled
    cpupower.service                            disabled
    crond.service                               enabled 
    dbus-org.fedoraproject.FirewallD1.service   enabled 

9. Linux中如何启动、重启、停止、重载服务以及检查服务（如 httpd.service）状态

    # systemctl start httpd.service
    # systemctl restart httpd.service
    # systemctl stop httpd.service
    # systemctl reload httpd.service
    # systemctl status httpd.service
    # systemctl is-active httpd.service
    # systemctl enable httpd.service
    # systemctl disable httpd.service
    # systemctl kill httpd
    # systemctl status httpd

10. 挂载、卸载、重新挂载、重载系统挂载点并检查系统中挂载点状态

    # systemctl start tmp.mount
    # systemctl stop tmp.mount
    # systemctl restart tmp.mount
    # systemctl reload tmp.mount
    # systemctl status tmp.mount

11.服务的CPU利用率（分配额）

    #获取当前某个服务的CPU分配额
    systemctl show -p CPUShares httpd.service  
    CPUShares=1024
    #将某个服务（httpd.service）的CPU分配份额限制为2000 CPUShares/
    systemctl set-property httpd.service CPUShares=2000
    systemctl show -p CPUShares httpd.service
    CPUShares=2000
    #检查某个服务的所有配置细节
	systemctl show httpd
	#分析某个服务（httpd）的关键链
	systemd-analyze critical-chain httpd.service
	#获取某个服务（httpd）的依赖性列表
	systemctl list-dependencies httpd.service
	#

12.控制系统运行等级

	#启动系统救援模式
	systemctl rescue
		Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):
		The system is going down to rescue mode NOW!
	#进入紧急模式
	systemctl emergency
		Welcome to emergency mode! After logging in, type "journalctl -xb" to view
		system logs, "systemctl reboot" to reboot, "systemctl default" to try again
		to boot into default mode.
	#列出当前使用的运行等级
	systemctl get-default
		multi-user.target