解决vsftpd连接变慢的情况

网上查询vsftpd连接慢的问题后，发现有人提出reverse_lookup_enable参数可能会出现较大的延迟。关于该数的man信息如下：

reverse_lookup_enable
Set to YES if you want vsftpd to transform the ip address into the hostname, before pam 
authentication. This is useful if you use pam_access including the hostname. If you want 
vsftpd to run on the environment where the reverse lookup for some hostname is available 
and the name server doesn’t respond for a while, you should set this to NO to avoid a 
performance issue.
Default: YES
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既然默认是YES，而且是其会尝试反解析，这里就修改下，在/etc/vsftpd/vsftpd.conf文件中增加reverse_lookup_enable=NO，并重启vsftpd服务后，问题解决。