Port 513
login and who · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | login and who |
Frequently asked questions
What is port 513 used for?
Port 513 is registered with the IANA for login and who (TCP/UDP). Description: remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"; maintains data bases showing who's logged in to machines on a local net and the load average of the machine.
Is port 513 a well-known port?
Yes. Port 513 is in the range 0–1023 (system or well-known ports). On Linux and macOS only privileged processes may bind to these ports.
How do I check whether port 513 is open?
Locally on Linux with ss -tulpn | grep ':513\b', on Windows with netstat -ano | findstr :513. To test a remote host use Test-NetConnection <host> -Port 513 in PowerShell or nc -zv <host> 513 on Linux/macOS.
How do I open port 513 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 513/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=513/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 513" -Direction Inbound -Protocol TCP -LocalPort 513 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | login | remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains" |
| UDP | who | maintains data bases showing who's logged in to machines on a local net and the load average of the machine |