-- How can I free a busy port ? --

[OLIVA_1]

Hello,

How can I free a busy port ?
I would like free the port 4200, how can I do ?

netstat -anf inet | grep 4200
tcp 0 0 57.7.6.213.52702 57.7.6.213.4200 ESTABLISHED
tcp 0 0 57.7.6.213.52654 57.7.6.213.4200 FIN_WAIT_2
tcp 0 0 57.7.6.213.51627 57.7.6.213.4200 FIN_WAIT_2
tcp 0 0 57.7.6.213.49433 57.7.6.213.4200 FIN_WAIT_2
tcp 0 0 57.7.6.213.4200 *.* LISTEN
tcp 0 0 57.7.6.213.4200 57.7.6.213.49433 CLOSE_WAIT
tcp 0 0 57.7.6.213.4200 57.7.6.213.51627 CLOSE_WAIT
tcp 0 0 57.7.6.213.4200 57.7.6.213.52654 CLOSE_WAIT
tcp 0 0 57.7.6.213.4200 57.7.6.213.52702 ESTABLISHED


Thanks,

[Mark Grant]

Ideally, you'll find out which application is listening on that port and stop it. Other than that it's quite difficult achieve I think though not impossible with some smart C that is too smart for my C

[Zigor Buruaga]

Hi,

Try stopping the program that use that port. If you don't know which is the program you can use "lsof" to find it.

HTH
Kind regards,
Zigor

[Massimo Bianchi]

kill a socket

The unorthodox method of using tcp_discon or tcp_discon_by_addr allows terminating of connections in the connections table without the need for a reboot. However, my advice is to use it only as a last resort.

To use the ndd -set /dev/tcp tcp_discon, you need the pointer to the TCP instance data. You can retrieve this via the ndd command tcp_status.

So, the scenario to find the TCP instance data and then use tcp_discon to remove the instance is as follows:

# ndd -get /dev/tcp tcp_status
TCP dest snxt suna swnd cwnd rnxt rack rwnd rto mss [lport,fport] state

0183b8b4 015.043.233.086 533cb8ce 533cb8ce 00008000 00003000 533bc583 533bc583 00000000 02812 04096 [c00a,cea9] TCP_CLOSE_WAIT

So, if you wanted to remove this connection:
# ndd -set /dev/tcp tcp_discon 0x0183b8b4

If you want to use the tcp_discon_by_addr, you use a 24 byte string that contains the hex representation of the quadruple.

For example, if the connection that I want to delete is:

Local IP: 192.1.2.3 (0xc0010203)
Local Port: 1024 (0x0400)
Remote IP : 192.4.5.6 (0xc0040506)
Remote Port: 2049 (0x0801)

The "hex" string you pass to tcp_discon_by_addr is:

# ndd -set /dev/tcp tcp_discon_by_addr "c00102030400c00405060801"

NOTE: the preceding 0x that typically indicates a Hex number is NOT part of the string passed.

Hope this helps. Regards.

[T G Manikandan · Accepted solution]

get lsof and then do a

#lsof -i tcp:4200

check for the application processes which use it and then you can stop them