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Abstract Domain Socket

lastmod 2022-03-03created 2022-03-032 edits

How to use/check

It means that when you use a unix domain socket, you don't have to use an actual file path. In this case, it is treated simply as a name rather than a file... (abstract domain socket) When you open the /proc/net/unix file or look with the netstat command, an @ is prepended to the file name to tell them apart.

To use it, put '\0' in the first byte of sun_path in the sockaddr_un struct, and then write the file path after it. 

    struct sockaddr_un serveraddr;

    bzero(&serveraddr, sizeof(serveraddr));
    serveraddr.sun_family = AF_UNIX;
    serveraddr.sun_path[0] = '\0';
    strcpy(&serveraddr.sun_path[1], "/path/to/non-exist");

    ret = bind(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));
    ...

With the following command, 

$ netstat -anp | grep a.out

it is shown as follows: 

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
unix  2      [ ]         DGRAM                    189653   3374/a.out          @/path/to/non-exist

See the abstract part of the Address Format section in the man page of unix(7). (man -7 unix)

See also

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