项目中涉及到物联网设备连接，需要用到mqtt。小试了一把emqx的安装，居然碰到了问题。小记一下，后续备查。

centos8下，安装流程很简单：

1、安装依赖包

yum install -y yum-utils device-mapper-persistent-data lvm2

2、设置安装源

yum-config-manager --add-repo 

3、安装最新版本的emqx

yum -y install emqx

整个安装过程简洁流畅。但启动的时候报错了：

systemctl start emqx

等半天后，提示：

Job for emqx.service failed because the control process exited with error code.See "systemctl status emqx.service" and "journalctl -xe" for details.

难道跟centos8不兼容？刚好手边有一台闲置的centos7.6的VPS，登录后重复上面安装流程，启动服务，完全没压力！没道理啊。回到centos8下，打开错误日志看下：

cat /var/log/emqx/erlang.log.1 ========== LOGGING STARTED Tue Jan 12 11:56:37 CST 2021=====Exec: /usr/lib/emqx/erts-10.7/bin/erlexec -boot /usr/lib/emqx/releases/4.2.5/emqx -mode embedded -boot_var ERTS_LIB_DIR /usr/lib/emqx/erts-10.7/../lib -mnesia dir "/var/lib/emqx/mnesia/emqx@127.0.0.1" -config /var/lib/emqx/configs/app.2021.01.12.11.56.37.config -args_file /var/lib/emqx/configs/vm.2021.01.12.11.56.37.args -vm_args /var/lib/emqx/configs/vm.2021.01.12.11.56.37.args -start_epmd false -epmd_module ekka_epmd -proto_dist ekka -- consoleRoot: /usr/lib/emqx/usr/lib/emqx{"Kernel pid terminated",application_controller,"{application_start_failure,kernel,{{shutdown,{failed_to_start_child,kernel_safe_sup,{on_load_function_failed,crypto}}},{kernel,start,[normal,[]]}}}"}Kernel pid terminated (application_controller) ({application_start_failure,kernel,{{shutdown,{failed_to_start_child,kernel_safe_sup,{on_load_function_failed,crypto}}},{kernel,start,[normal,[]]}}})Crash dump is being written to: /var/log/emqx/crash.dump...done

关键词："Kernel pid terminated"，放狗搜下，看到有文章在讨论这个话题，可能是跟一个compat-openssl10的库有关。

centos8下，装上：

yum install compat-openssl10

再启动服务，岁月静好！

所以，centos8下，第一步安装依赖库应该改为：

yum install -y yum-utils device-mapper-persistent-data lvm2 compat-openssl10

参考文章：