UDP -- Socket - bind error - Address already in use?

Question

I see that the address is already in use on bind() while the system is starting up.

When I reload the system plenty of times, I see that once in a while like 1 out of 100, I see the following error:

bind failed.Error: Address already in use.

On every reboot of the system - I am closing the socket by using close(gTx.i4TxSockId).

Here is the code, I am not sure on how can I debug this.

I have added netstat -ap to find out what problem was it.

On success, I see:

netstat: /proc/net/tcp6: No such file or directory
udp        0      0 0.0.0.0:syslog          0.0.0.0:*                           1562/syslog-ng
udp        0      0 0.0.0.0:49155           0.0.0.0:*                           1817/App.exe

On failure, I see:

netstat: /proc/net/tcp6: No such file or directory
udp        0      0 0.0.0.0:45825           0.0.0.0:*                           1816/App.exe
udp        0      0 0.0.0.0:syslog          0.0.0.0:*                           1562/syslog-ng
udp        0      0 localhost:49155         0.0.0.0:*                           1816/App.exe

I have added the following line:

if (setsockopt(gTx.i4TxSockId, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int)) < 0)
{
    perror("Failed in SO_REUSEADDR");
    return;
}

This is not making any difference.

I am using embedded linux - version - 3.8.8

struct sockaddr_in  LocalAddr;

gTx.i4TxSockId = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);

if (gTx.i4TxSockId < 0)
{
    printf("Error in opening socket");
    return ;
}

if (setsockopt(gTx.i4TxSockId, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int)) < 0)
{
    perror("Failed in SO_REUSEADDR");
    return;
}

LocalAddr.sin_family = AF_INET;
LocalAddr.sin_addr.s_addr = INADDR_ANY;
LocalAddr.sin_port = HTONS(49155);

/* Bind with the socket */
if (bind (gTx.i4TxSockId, (struct sockaddr *) &LocalAddr, sizeof (struct sockaddr_in)) < 0)
{
    /* Failure in binding the UDP socket */
    perror("bind failed.Error");
    return;
}

It's unlikely the cause of the problem but recently I learned that it should be `PF_INET` instead of `AF_INET`. Normally I think `AF_INET` is just `#define AF_INET PF_INET`. But the correct constant is `PF_INET`. — Iharob Al Asimi, May 25 '16 at 00:20
Perhaps you mean `(int[]){1}` instead, [read this](http://stackoverflow.com/a/6117081/1983495) — Iharob Al Asimi, May 25 '16 at 00:27
@iharob: [What is the difference between AF_INET and PF_INET in socket programming?](http://stackoverflow.com/questions/6729366/) — Remy Lebeau, May 25 '16 at 00:29
@iharob: it would be safer to use an actual variable instead of trying to type-cast a temp array. `setsockopt()` is expecting a pointer to a variable: `int flag = 1; setsockopt(..., &flag, sizeof(flag));` Also, don't forget that Linux also has an `SO_REUSEPORT` option. — Remy Lebeau, May 25 '16 at 00:33
@RemyLebeau Interesting link, and that's what I would do too. It doesn't bother me to use an extra variable. But certainly the code is incorrect and it might be what was meant. And since Beej's explains it and it makes a lot of sense it's weird that we don't see `#define PF_INET AF_INET` instead. — Iharob Al Asimi, May 25 '16 at 00:37

score 0 · Accepted Answer · answered Jul 04 '16 at 04:35

0

I got to know that I can reserve the port in rcS file -

sysctl -w net.ipv4.ip_local_reserved_ports=49155

answered Jul 04 '16 at 04:35

dexterous

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UDP -- Socket - bind error - Address already in use?

1 Answers1