Postfix发送邮件时报错“libmysqlclient.so.18: cannot open shared object file: No such file or directory”

在一台Linux服务器上使用postfix发送邮件时遇到上面错误:

sendmail.postfix: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory

Error sending message, child exited 127 (Exec error.).

检查和启动postfix服务时，报下面错误：

# systemctl status postfix      

● postfix.service - Postfix Mail Transport Agent      

Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)      

Active: failed (Result: exit-code) since Sun 2022-03-13 08:30:32 CST; 6s ago      

Process: 235712 ExecStart=/usr/sbin/postfix start (code=exited, status=127)      

Process: 235709 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)      

Process: 235705 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=127)      

Mar 13 08:30:32 xxx-xxx-DB01 systemd[1]: Starting Postfix Mail Transport Agent...      

Mar 13 08:30:32 xxx-xxx-DB01 aliasesdb[235705]: /usr/sbin/postconf: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory      

Mar 13 08:30:32 xxx-xxx-DB01 aliasesdb[235705]: /usr/bin/newaliases: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory      

Mar 13 08:30:32 xxx-xxx-DB01 postfix[235712]: /usr/sbin/postfix: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory      

Mar 13 08:30:32 xxx-xxx-DB01 systemd[1]: postfix.service: control process exited, code=exited status=127      

Mar 13 08:30:32 xxx-xxx-DB01 systemd[1]: Failed to start Postfix Mail Transport Agent.      

Mar 13 08:30:32 xxx-xxx-DB01 systemd[1]: Unit postfix.service entered failed state.      

Mar 13 08:30:32 xxx-xxx-DB01 systemd[1]: postfix.service failed.      

出现个错误的原因是找不到libmysqlclient.so.18这个文件，根本原因：要在这台机器上测试MySQL升级，我卸载MySQL时，将/usr/lib64/mysql/这个目录给清理了，也导致/usr/lib64/mysql/libmysqlclient.so.18文件被删除了，从而引起了这个问题。

解决方案：

　　1、因为这台Linux服务器是从生产环境克隆的，所以，我们可以将生产服务器上的libmysqlclient.so.18拷贝克隆过来。放到MySQL 5.7.36的安装目录下去。当前MySQL 5.7.36的lib目录，你可以看到没有libmysqlclient.so.18，只有libmysqlclient.so.20等文件，如下所示：

$ ls -lrt      

total 1016992      

-rw-r--r-- 1 mysql mysql 404983716 Sep  7  2021 libmysqld-debug.a      

-rw-r--r-- 1 mysql mysql     43494 Sep  7  2021 libmysqlservices.a      

-rwxr-xr-x 1 mysql mysql   9518856 Sep  7  2021 libmysqlclient.so.20.3.23      

-rw-r--r-- 1 mysql mysql  21915440 Sep  7  2021 libmysqlclient.a      

-rw-r--r-- 1 mysql mysql 595352594 Sep  7  2021 libmysqld.a      

lrwxrwxrwx 1 mysql mysql        25 Sep  7  2021 libmysqlclient.so.20 -> libmysqlclient.so.20.3.23      

lrwxrwxrwx 1 mysql mysql        20 Sep  7  2021 libmysqlclient.so -> libmysqlclient.so.20      

drwxr-xr-x 2 mysql mysql        28 Mar  8 13:11 pkgconfig      

drwxr-xr-x 4 mysql mysql        28 Mar  8 13:11 mecab      

drwxr-xr-x 3 mysql mysql      4096 Mar  8 13:11 plugin      

　　2、然后编辑/etc/ld.so.conf文件，在文件后面增加一条记录：/data/mysql/mysql5.7/lib （libmysqlclient.so.18 和libmysqlclient.so.18.0.0所在目录），运行ldconfig 命令，让其生效。

下面是具体的操作步骤。

# mv libmysqlclient.so.18  /data/mysql/mysql5.7/lib/

# echo "/data/mysql/mysql5.7/lib" >> /etc/ld.so.conf

# ldconfig

# systemctl start postfix

ld.so.conf文件

/etc/ld.so.conf 此文件记录了编译时使用的动态库的路径，也就是加载so库的路径。