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FreeBSD 11.0 - man page for getpeereid (freebsd section 3)

GETPEEREID(3)						   BSD 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) have been called. The effective used 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 cre- dentials 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 indi- cate 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.
BSD
July 15, 2001 BSD