if you have to monitor and/or debug ftp / sftp traffic for problems you can use following commands:

  • tail -f /var/log/vsftpd.log
  • watch -d -n 1 ‘sudo netstat -tan|grep \:21’
  • sudo iftop -B -f “port ftp”

Sources:

  • http://www.webhostingtalk.com/showthread.php?t=1615072