About
This page is about Port management on Linux.
When you install a software (process), you need often to verify the available port in order to configure the component installation.
How to find which process uses a port?
with netstat, you can check port.
For example, below, you can see that the port 1521 is used to the program tnslsnr (The -p parameters means program and is mandatory)
netstat -tulpn | grep 1521
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
Protocol Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 :::1521 :::* LISTEN 4264/tnslsnr
where:
- The protocol (tcp, udp, raw) used by the socket.
- Recv-Q: The count of bytes not copied by the user program connected to this socket.
- Send-Q The count of bytes not acknowledged by the remote host.
- Local Address: Address and port number of the local end of the socket. Unless the –numeric (-n) option is specified, the socket address is resolved to its canonical host name (FQDN), and the port number is translated into the corresponding service name.
- Foreign Address: Address and port number of the remote end of the socket. Analogous to “Local Address.”
- State: The state of the socket (ESTABLISHED, LISTEN, …)
- PID/Program name: Slash-separated pair of the process id (PID) and process name of the process that owns the socket.
How to check a port remotely?
with Network - netcat (nc, ncat)
- Check one port
nc -zv hostname port
DNS fwd/rev mismatch: hostname != hostname.lan
hostname [192.168.135.6] 9000 (?) open
How to see the ports used by well-known services?
To see the port used by services, you can inspect the services file (The services translation file), located at:
/etc/services