按照https://www.cnblogs.com/micq/articles/6170194.html
遇到500错误，用下面的方法解决的
I had the same problem recently, I also got the message:
500 OOPS: failed to open xferlog log file:/var/log/xferlog
This is what I did:
Open a terminal
Switch to root using su -
service vsftpd stop
Wait for the message: Shutting down vsftpd: [ OK ]
After this I removed the log file
rm /var/log/vsftpd.log
Type "y" for the question: rm: remove regular file `/var/log/vsftpd.log'?
service vsftpd start
After I did this everything worked OK.
vsftpd created a new log file in /var/log/ and it logged every upload/download.
I hope this have helped you.
不知道为什么换电脑后就登录不了。。。折腾了一天了，好累啊