一个客户向我抱怨：在MySQL查询小表没有问题，查询大表出错，下面是他发给我的出错的部分截屏（客户的表名被我隐藏了）。

这里的给出的信息已经比较明显了，是向/tmp目录中创建临时表失败（临时表的路径是由系统变量tmpdir决定的，默认在/tmp目录中），小表不需要用到临时表就没有问题，我登录上去检查一下MySQL的错误日志，发现有下面的记录：

2024-01-27T09:31:14.059966Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ib9IqGPN' (OS errno 13 - Permission denied)
2024-01-27T09:31:14.060056Z 0 [ERROR] [MY-012792] [InnoDB] Cannot create temporary merge file
2024-01-27T09:32:22.698498Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ibuFD5pG' (OS errno 13 - Permission denied)
2024-01-27T09:32:22.698617Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ibJyUu0y' (OS errno 13 - Permission denied)
2024-01-27T09:32:22.698786Z 0 [ERROR] [MY-012792] [InnoDB] Cannot create temporary merge file
2024-01-27T09:32:22.698783Z 0 [ERROR] [MY-012792] [InnoDB] Cannot create temporary merge file

24-01-27T09:30:06.361749Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ibivRI0I' (OS errno 13 - Permission denied)
2024-01-27T09:30:06.361920Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ibx78TGm' (OS errno 13 - Permission denied)
2024-01-27T09:30:06.361864Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/ibdcjrzB' (OS errno 13 - Permission denied)
2024-01-27T09:30:06.361955Z 0 [ERROR] [MY-013129] [Server] A message intended for a client cannot be sent there as no client-session is attached. Therefore, we're sending the information to the error-log instead: MY-000001 - Can't create/write to file '/tmp/iblFGa8t' (OS errno 13 - Permission denied)

看来是/tmp目录的权限出了问题，检查一下：

oracle@Scott ~$ ll -ld /tmp
drwxrwxrwt. 11 root root 4096 Jan 29 09:22 /tmp
oracle@Scott ~$

[root@oracle data]# ll -ld /tmp
drwxr-xr-x. 70 root root 630784 Jan 29 09:40 /tmp

发现权限不足，而且居然没有粘滞位（Sticky bit），粘滞位是Unix文件系统权限的一个旗标。最常见的用法在目录上设置粘滞位，如此以来，只有目录内文件的所有者或者root才可以删除或移动该文件。如果不为目录设置粘滞位，任何具有该目录写和执行权限的用户都可以删除和移动其中的文件。实际应用中，粘滞位一般用于/tmp目录，以防止普通用户删除或移动其他用户的文件。使用下面的命令对tmp目录进行修改：

sudo chmod 1777 /tmp 

然后故障排除😀