Solution to ftp connection failure suddenly

Ideas:

1. Is selinux enabled?
2. Whether the specified ftp port is added to iptbales
3. Whether the FTP service is enabled

SEARCH command:

1. cat:/etc/selinux/config
Check whether SELINUX = disable is disabled.

2. cat/etc/sysconfig/iptables
Check whether the firewall has enabled the specified ftp port

3,
1) run the getsebool ftpd_disable_trans command to check the current status if it is not on
2) enter the command: setsebool ftpd_disable_trans 1
Of course, you can also add the-P Parameter so that you do not need to enter this command every time you start the system.
Setsebool-P ftpd_disable_trans 1

At last, we found that the ftp status is on. If it is enabled, ftp can be connected.