crond定时任务详解crond是Linux下用来周期性的执行某种任务或等待处理某些事件的一个守护进程，可以在无需人工干预的情况下运行作业。我的环境是3A服务器搭建centos7.9，延迟低安装crond服务yuminsta

打开终端cd/Java(https://www.oschina.net/action/GoToLink?urlhttp%3A%2F%2Flib.csdn.net%2Fbase%2Fjavase)/tomcat执行bin/startup.sh启动tomcat./startup.shbin/shutdown.sh停止tomc

1.查看服务状态: psef|grepmysqld !(https://static.oschina.net/uploads/space/2017/0705/140416_7Ew0_3434392.png)servicemysqldstatus 

准备环境：3台linux虚拟主机，zookeeper安装包，zookeeper版本号是3.4.6，本文zookeeper安装在/usr/local目录下一、首先下载zookeepercd/usr/localwget http://apache.org/dist/zookeeper/zookeeper3.4.6/zookeeper3.4.6

下载JDKhttp://www.oracle.com/technetwork/java/javase/downloads/index.html(https://www.oschina.net/action/GoToLink?urlhttp%3A%2F%2Fwww.oracle.com%2Ftechnetwork%2Fjava%2Fjavas

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是否已经安装了AIO包rpmqa|grepaiolibaio0.3.10710.el6.x86\_64libaiodevel0.3.10710.el6.x86\_64libsanehpaio3.12.44.el6\_4.1.x86\_64数据库在链接时是否已经加载了aio的包$/us

进入单用户模式进行修改root密码重启之后按e键进入编辑；编辑修改：方向键一直往下按，在以linux16开头行末尾  加入rd.breakconsoletty0  ，ctrlx继续运行挂载磁盘，重置root密码；switchrootmountoremount,rw/sysroot/重新挂载将ro状态变为rw；switchroo