Port 20 — FTP data

TCP well-known

What runs on port 20

The data channel of the classic File Transfer Protocol. The control channel is port 21.

Security considerations

Unencrypted. Use SFTP (port 22) or FTPS instead — plain FTP sends credentials in clear text.

Checking whether something is listening

# Linux / macOS — what is bound to the port
sudo lsof -i :20
sudo ss -lntp | grep :20

# Windows
netstat -ano | findstr :20
Get-NetTCPConnection -LocalPort 20

# is it reachable from outside?
nc -zv example.com 20
curl -v telnet://example.com:20

Freeing the port

# find the process, then stop it
sudo lsof -ti :20 | xargs kill        # Linux / macOS
netstat -ano | findstr :20            # note the PID, then:
taskkill /PID <pid> /F                    # Windows

Other common ports

• Port 21 — FTP control
• Port 22 — SSH / SFTP
• Port 23 — Telnet
• Port 25 — SMTP
• Port 53 — DNS
• Port 67 — DHCP server
• Port 68 — DHCP client
• Port 69 — TFTP
• Port 80 — HTTP
• Port 110 — POP3
• Port 123 — NTP
• Port 143 — IMAP
• Port 161 — SNMP
• Port 389 — LDAP
• Port 443 — HTTPS
• Port 445 — SMB
• Port 465 — SMTPS
• Port 514 — Syslog

All port numbers