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About c : Bind-failed-Address-already-in-use

Question Detail

I am attempting to bind a socket to a port below:

if( bind(socket_desc,(struct sockaddr *) &server, sizeof(server)) < 0)
    perror("bind failed. Error");
    return 1;
puts("bind done");

But it gives:

$ ./serve   
Socket created    
bind failed. Error: Address already in use

Why does this error occur?

Question Answer

Everyone is correct. However, if you’re also busy testing your code your own application might still “own” the socket if it starts and stops relatively quickly. Try SO_REUSEADDR as a socket option:

What exactly does SO_REUSEADDR do?

This socket option tells the kernel that even if this port is busy (in
the TIME_WAIT state), go ahead and reuse it anyway. If it is busy,
but with another state, you will still get an address already in use
error. It is useful if your server has been shut down, and then
restarted right away while sockets are still active on its port. You
should be aware that if any unexpected data comes in, it may confuse
your server, but while this is possible, it is not likely.

It has been pointed out that “A socket is a 5 tuple (proto, local
addr, local port, remote addr, remote port). SO_REUSEADDR just says
that you can reuse local addresses. The 5 tuple still must be
unique!” by Michael Hunter ([email protected]). This is true, and this
is why it is very unlikely that unexpected data will ever be seen by
your server. The danger is that such a 5 tuple is still floating
around on the net, and while it is bouncing around, a new connection
from the same client, on the same system, happens to get the same
remote port. This is explained by Richard Stevens in “2.7 Please
explain the TIME_WAIT state.”.

You have a process that is already using that port. netstat -tulpn will enable one to find the process ID of that is using a particular port.

Address already in use means that the port you are trying to allocate for your current execution is already occupied/allocated to some other process.

If you are a developer and if you are working on an application which require lots of testing, you might have an instance of your same application running in background (may be you forgot to stop it properly)

So if you encounter this error, just see which application/process is using the port.

In linux try using netstat -tulpn. This command will list down a process list with all running processes.

Check if an application is using your port. If that application or process is another important one then you might want to use another port which is not used by any process/application.

Anyway you can stop the process which uses your port and let your application take it.

If you are in linux environment try,

  • Use netstat -tulpn to display the processes
  • kill <pid> This will terminate the process

If you are using windows,

  • Use netstat -a -o -n to check for the port usages
  • Use taskkill /F /PID <pid> to kill that process

The error usually means that the port you are trying to open is being already used by another application. Try using netstat to see which ports are open and then use an available port.

Also check if you are binding to the right ip address (I am assuming it would be localhost)

As mentioned above the port is in use already.
This could be due to several reasons

  1. some other application is already using it.
  2. The port is in close_wait state when your program is waiting for the other end to close the program.refer (https://unix.stackexchange.com/questions/10106/orphaned-connections-in-close-wait-state).
  3. The program might be in time_wait state. you can wait or use socket option SO_REUSEADDR as mentioned in another post.

Do netstat -a | grep <portno> to check the port state.

if address is already in use can you just want to kill whoso ever process is using the port, you can use

lsof -ti:PortNumberGoesHere | xargs kill -9

source and inspiration this.

PS: Could not use netstat because it not installed already.

It also happens when you have not give enough permissions(read and write) to your sock file!

Just add expected permission to your sock contained folder and your sock file:

 chmod ug+rw /path/to/your/
 chmod ug+rw /path/to/your/file.sock

Then have fun!

I was also facing that problem, but I resolved it.
Make sure that both the programs for client-side and server-side are on different projects in your IDE, in my case NetBeans. Then assuming you’re using localhost, I recommend you to implement both the programs as two different projects.

To terminate all node processes:

killall -9 node

First of check which port are listening,

netstat -tlpn

then select available port to conect,

sudo netstat -tlpn | grep ':port'

Fix it into also to your server and clients interfaces. Go Barrier tab -> change settings, -> port value type -> save/ok

Check both clients and server have similar port values

Then Reload.

Now it should be ok.

Check for running process pid:

pidof <process-name>

Kill processes:

sudo kill -9 process_id_1 process_id_2 process_id_3

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