Answer:

Usually, the exit code 255 is a frequent error that happens due to the problem in SSH access.

The Following would be the reason for that SFTP error

1. Missing RSA key
3. Firewall restrictions

we check the IPtables to see if there are any IP restrictions.

      iptables -nL | grep xx.xx.xx.xx

1. Permission of sftp

Here, we check the permission of the user and .ssh folder and correct it as follows.

     chmod 755 /home/user
     chmod 700 /home/user/.ssh