GETPEEREID(3) | 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) 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.

# IMPLEMENTATION NOTES

On NetBSD, `getpeereid`() is implemented in terms of the `LOCAL_PEEREID` 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) have been called nor one returned from listen(2).
[`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 NetBSD 5.0.

August 8, 2007 | NetBSD 9.5