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I have a specific service that sends data on port 5555. I need to open socket on shell unix to listen on this port and print output on shell. Service is deployed as docker container. So, I run container binding port 5555:5555.

I tried to run nc -l localhost 5555 on my host but it not work. I tried to open container shell and run netstat. This is the output:

# netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       
tcp        0      0 localhost:epmd          localhost:49664         ESTABLISHED 
tcp        0      0 localhost:49664         localhost:epmd          ESTABLISHED 
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags       Type       State         I-Node Path
unix  3      [ ]         STREAM     CONNECTED      98194 
unix  3      [ ]         STREAM     CONNECTED      98193 
unix  3      [ ]         STREAM     CONNECTED      99655

I'm sure that service sends data but I cannot receve. Can you help me? Thanks

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  • Do you need to listen on TCP or UDP? Is the container binding done on localhost address or on an actual IP on an (bridge)-interface? Commented Jun 15, 2022 at 8:51
  • I need to open on UDP. Container is run on remote host using -p 5555:5555 in docker run comand. I prefer to listen from remote host but to be able to listen from localhost can be a first good result. Can nc -l localhost 5555 used to listen from Unix socket? Thanks Commented Jun 15, 2022 at 8:54
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    You need to specify -u to listen on UDP sockets, -U for unix domain sockets. Commented Jun 15, 2022 at 9:06
  • Thanks for the help. Now its work from my container shell. I used ``` nc -u -l localhost -p 5555. I add -u and -p option. Now, It does not work from remote host. Using nc -u -l remoteIP -p 5555``` I dont' receve anything. Reading documentation is not necessary set particulary option to listen from remote host. I'm able to connect to remoteIP. Commented Jun 15, 2022 at 9:45
  • You would specify nc -l -u IP PORT to listen and use udp, then bind (locally) to the IP on port PORT. When you want to receive data from a remote host, IP cannot be localhost but must be the address of an actually connected interface. Commented Jun 15, 2022 at 11:05

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