CentOS 7 开机延迟解决办法

遇到这种情况 , 开机延迟 ,  可以用下面的办法来查看 , 寻找到问题的源头 , 来看看到的是怎么回事

[root@DaMoWang ~]# dmesg |grep udev 　　 #显示系统的启动信息 , 从中过滤udev
[    1.088863] systemd[]: Listening on udev Control Socket.
[    1.088869] systemd[]: Starting udev Control Socket.
[    1.088889] systemd[]: Listening on udev Kernel Socket.
[    1.088893] systemd[]: Starting udev Kernel Socket.
[root@DaMoWang ~]# journalctl -k |grep udev 　　#查看系统本次启动的日志 , 从中过滤udev
7月  :: DaMoWang.localdomain systemd[]: Listening on udev Control Socket.
7月  :: DaMoWang.localdomain systemd[]: Starting udev Control Socket.
7月  :: DaMoWang.localdomain systemd[]: Listening on udev Kernel Socket.
7月  :: DaMoWang.localdomain systemd[]: Starting udev Kernel Socket.

这看不出有什么问题 , 下面来一项一项的找 , 看看到底等待的是哪个服务

 

[root@DaMoWang ~]# systemd-analyze blame 　　　　#查看每个服务的启动耗时
      2min 586ms systemd-udev-settle.service
         .258s NetworkManager-wait-online.service
         .640s mysqld.service
         .771s tuned.service
         .301s named.service
         .617s postfix.service
         .201s polkit.service
         .604s ModemManager.service
         .135s dev-mapper-centos\x2droot.device
          .747s lvm2-monitor.service
          .636s systemd-logind.service
          .626s rpcbind.service
          .621s sysstat.service
          .589s gssproxy.service
          .588s named-setup-rndc.service
          .495s avahi-daemon.service
          .477s rhel-dmesg.service
          .612s httpd.service
          .934s chronyd.service
          .524s abrt-ccpp.service
          .783s vdo.service
          .039s network.service
          .982s auditd.service
          .306s boot.mount
          .027s systemd-tmpfiles-setup-dev.service
          .927s NetworkManager.service
          .670s systemd-udevd.service
          .292s lvm2-pvscan@:.service
          .272s rhel-readonly.service
          .019s lvm2-pvscan@:.service
          .797s lvm2-pvscan@:.service
          .788s dmraid-activation.service
          .761s lvm2-pvscan@:.service
          .679s lvm2-pvscan@:.service
          .462s sshd.service
          .327s rhel-domainname.service
          .267s plymouth-read-write.service
          .213s [e-mail]
          .212s rsyslog.service
           880ms systemd-tmpfiles-setup.service
           817ms dev-hugepages.mount
           761ms systemd-remount-fs.service
           759ms sys-kernel-debug.mount
           758ms dev-mqueue.mount
           696ms nfs-config.service
           686ms rhel-import-state.service
           644ms kmod-static-nodes.service
           585ms systemd-journald.service
           488ms systemd-user-sessions.service

#下面还有很多服务 , 不过不需要看 , 只需要找到时间最长的那个服务就可以了

通过运行 systemd 分析，发现 systemd-udev-setle.service 是造成延迟的原因 

[root@DaMoWang ~]# systemctl mask systemd-udev-settle     #屏蔽掉这个服务
Created symlink from /etc/systemd/system/systemd-udev-settle.service to /dev/null.