解决 CDH6 启动 cloudera-scm-server 失败问题

最近尝试在 CentOS7 上使用 Cloudera CM 搭建 CDH6 的集群，安装好了 cloudera-manager-daemons 、 cloudera-manager-agent 、 cloudera-manager-server 后，通过 systemctl start cloudera-scm-server ，一直没有成功启动服务。

看到的都报错的信息：

● cloudera-scm-server.service - Cloudera CM Server Service Loaded: loaded (/usr/lib/systemd/system/cloudera-scm-server.service; enabled; vendor preset: disabled) Active: failed (Result: start-limit) since Thu 2020-09-10 17:03:36 CST; 4s ago Process: 5045 ExecStart=/opt/cloudera/cm/bin/cm-server (code=exited, status=1/FAILURE) Process: 5042 ExecStartPre=/opt/cloudera/cm/bin/cm-server-pre (code=exited, status=0/SUCCESS) Main PID: 5045 (code=exited, status=1/FAILURE)

Sep 10 17:03:36 cdh1 systemd[1]: cloudera-scm-server.service: main process exited, code=exited, status=1/FAILURE Sep 10 17:03:36 cdh1 systemd[1]: Unit cloudera-scm-server.service entered failed state. Sep 10 17:03:36 cdh1 systemd[1]: cloudera-scm-server.service failed. Sep 10 17:03:36 cdh1 systemd[1]: cloudera-scm-server.service holdoff time over, scheduling restart. Sep 10 17:03:36 cdh1 systemd[1]: Stopped Cloudera CM Server Service. Sep 10 17:03:36 cdh1 systemd[1]: start request repeated too quickly for cloudera-scm-server.service Sep 10 17:03:36 cdh1 systemd[1]: Failed to start Cloudera CM Server Service. Sep 10 17:03:36 cdh1 systemd[1]: Unit cloudera-scm-server.service entered failed state. Sep 10 17:03:36 cdh1 systemd[1]: cloudera-scm-server.service failed.

而且没有任何更多的日志，包括 /var/log/cloudera-scm-server/ 目录也没有任何文件。

然后通过命令 journalctl -xe 发现了一些端倪，提示 JAVA_HOME 找不到，但是我明明已经安装过了jdk，使用 java -version 也可以正常列出版本信息，怎么还会找不到呢？之后在一个脚本文件中找到了些答案，原来程序默认会去使用 /usr/java 下的jdk，所以解决办法执行以下两条命令即可：

mkdir -p /usr/java
ln -s /opt/java/  /usr/java/default

再次执行就能正常的启动了：

systemctl status cloudera-scm-server ● cloudera-scm-server.service - Cloudera CM Server Service Loaded: loaded (/usr/lib/systemd/system/cloudera-scm-server.service; enabled; vendor preset: disabled) Active: active (running) since Thu 2020-09-10 17:08:18 CST; 3s ago Process: 5098 ExecStartPre=/opt/cloudera/cm/bin/cm-server-pre (code=exited, status=0/SUCCESS) Main PID: 5101 (java) CGroup: /system.slice/cloudera-scm-server.service

同时注意的是，集群内其他已经安装 Java 的机器也建议这样操作，因为 CDH 在安装过程也会检查集群内各个机器的环境情况，如果机器只是安装了 Java 并配合环境变量，但是 /usr/java 没有信息的话，检测也会提示机器没有 Java 环境的。