GETPEEREID(3)          FreeBSD Library Functions Manual          GETPEEREID(3)

NAME
     getpeereid - get the effective credentials of a UNIX-domain peer

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     int
     getpeereid(int s, uid_t *euid, gid_t *egid);

DESCRIPTION
     The getpeereid() function returns the effective user and group IDs of the
     peer connected to a UNIX-domain socket.  The argument s must be a
     UNIX-domain socket (unix(4)) of type SOCK_STREAM on which either
     connect(2) or listen(2) has been called.  The effective user ID is placed
     in euid, and the effective group ID in egid.

     The credentials returned to the listen(2) caller are those of its peer at
     the time it called connect(2); the credentials returned to the connect(2)
     caller are those of its peer at the time it called listen(2).  This
     mechanism is reliable; there is no way for either side to influence the
     credentials returned to its peer except by calling the appropriate system
     call (i.e., either connect(2) or listen(2)) under different effective
     credentials.

     One common use of this routine is for a UNIX-domain server to verify the
     credentials of its client.  Likewise, the client can verify the
     credentials of the server.

IMPLEMENTATION NOTES
     On FreeBSD, getpeereid() is implemented in terms of the LOCAL_PEERCRED
     unix(4) socket option.

RETURN VALUES
     The getpeereid() function returns the value 0 if successful; otherwise
     the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS
     The getpeereid() function fails if:

     [EBADF]            The argument s is not a valid descriptor.

     [ENOTSOCK]         The argument s is a file, not a socket.

     [ENOTCONN]         The argument s does not refer to a socket on which
                        connect(2) or listen(2) have been called.

     [EINVAL]           The argument s does not refer to a socket of type
                        SOCK_STREAM, or the kernel returned invalid data.

SEE ALSO
     connect(2), getpeername(2), getsockname(2), getsockopt(2), listen(2),
     unix(4)

HISTORY
     The getpeereid() function appeared in FreeBSD 4.6.

FreeBSD 13.1-RELEASE-p6        February 3, 2017        FreeBSD 13.1-RELEASE-p6