Home/ Questions/Q 829035
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-15T03:49:11+00:00

How do I check with C if a port on my local machine (if

  • 0

How do I check with C if a port on my local machine (if required by passing an IP or interface, too), is in listen state? I don’t want to connect to this port for checking because I don’t want to irritate the service behind this port.

I want to use this to add the missing net.tcp.listen item to Zabbix.

EDIT – THIS IS THE REAL ANSWER:

The correct way is to read the socket tables:

/proc/net/tcp
/proc/net/tcp6

They contain lines like:

sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
0: 00000000:1F40 00000000:0000 0A 00000000:00000000 00:00000000 00000000   101        0 4083927 1 f5d15240 750 0 0 2 -1
1: 00000000:2742 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1002        0 6100 1 decd76c0 750 0 0 2 -1

and can easily parsed for listening sockets (dst:00000000:0000). An strace on netstat shows that netstat works the same way.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Something like netstat ?

    `netstat -anp`

    Will list all the ports and should do the trick.

    Since this is open-source software, you can probably take some inspiration in it. And i believe it is written in C.

    • 0