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) has been called, or one returned from
accept(2) after
bind(2) and
listen(2) have been called. If non-NULL, the effective used ID is placed in
euid, and the effective group ID in
egid.
The credentials returned to the
accept(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
bind(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
bind(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.