FTP suddenly directly not connected to the solution _ftp server

Ideas:

1, SELinux problem is not open
2, iptbales or not to join the FTP specified port
3, the service is open FTP

Find command:

1. Cat:/etc/selinux/config
View SELINUX = Disable is in a closed state

2, Cat/etc/sysconfig/iptables
To see if the firewall opens the FTP specified port

3,
1, using the command: Getsebool Ftpd_disable_trans can view the current state if not on
2), input command: Setsebool Ftpd_disable_trans 1
Of course, you can add the-p parameter so that you don't have to enter this command every time you boot
Setsebool-p Ftpd_disable_trans 1

Finally found that the status of FTP is on, open, FTP can be connected.