Linux sockets: Difference between revisions
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Program crashes on
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For more information, see [http://man7.org/linux/man-pages/man7/socket.7.html socket(7)] and [http://man7.org/linux/man-pages/man7/ip.7.html ip(7)] manpages. |
For more information, see [http://man7.org/linux/man-pages/man7/socket.7.html socket(7)] and [http://man7.org/linux/man-pages/man7/ip.7.html ip(7)] manpages. |
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=== Program crashes on <code>write</code> with exit code -13 === |
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Exit code -13 means the program died because of SIGPIPE signal, meaning it tried to write to a closed socket. |
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Solutions: |
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* Ignore SIGPIPE in the program [https://stackoverflow.com/questions/16124019/writesocket-buff-length-makes-crash]: |
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<source lang="c"> |
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signal (SIGPIPE, SIG_IGN); |
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</source> |
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* Use <code>send</code> instead of <code>write</code>. Send returns -1 and set <code>errno</code> to <code>EPIPE</code> rather than generating a fatal SIGPIPE like <code>write</code> does [https://stackoverflow.com/questions/15793928/c-linux-tcp-ip-program-crashes-when-calling-write]: |
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<source lang="c"> |
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n = send(newsockfd, data.c_str(), data.length()+1, MSG_NOSIGNAL); |
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</source> |
Revision as of 05:10, 28 September 2018
Tutorials
- A thoough step-by-step example of client and socket code.
- Simple example of client and server code using Linux sockets.
References
- A very detailed answer about the differences between
SO_REUSEADDR
andSO_REUSEPORT
.
- A course on internet technologies, including Domain Naming (DNS...), the IP protocol, the TCP protocol, ...
- Manpages:
Troubleshooting
Use errno / perror / strerror to get error
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
printf("bind failed: %s (errno %d)", strerror(errno), errno);
return 1;
}
Or there is also the perror
function:
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
perror("bind failed");
return 1;
}
Use netstat
to get socket status
./server
# bind done
# Waiting for incoming connections...
# Connection accepted
# Handler assigned
# ^C
./server
# bind failed: Address already in use (errno 98)
netstat -a | grep 8888
# tcp 0 0 zavcxl0005:58888 165.225.76.32:http ESTABLISHED
# tcp 0 0 zavcxl0005:48888 10.75.126.1:https ESTABLISHED
# tcp 0 0 localhost.localdom:8888 localhost.localdo:50310 TIME_WAIT
# ... So port is still in use
bind failed: Address already in use (errno 98)
Call to bind
fails with error
bind failed: Address already in use (errno 98)
On a server, this is probably due to an old instance of the server that tries to bind to the same port and address [1].
As a fix, try to bind with option SO_REUSEADDR
and/or SO_REUSEPORT
. From SO:
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int)) < 0)
error("setsockopt(SO_REUSEADDR) failed");
For more information, see socket(7) and ip(7) manpages.
Program crashes on write
with exit code -13
Exit code -13 means the program died because of SIGPIPE signal, meaning it tried to write to a closed socket.
Solutions:
- Ignore SIGPIPE in the program [2]:
signal (SIGPIPE, SIG_IGN);
- Use
send
instead ofwrite
. Send returns -1 and seterrno
toEPIPE
rather than generating a fatal SIGPIPE likewrite
does [3]:
n = send(newsockfd, data.c_str(), data.length()+1, MSG_NOSIGNAL);