.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH NS_GET_OWNER_UID 2const 2025-05-17 "Linux man-pages 6.16"
.SH NAME
NS_GET_OWNER_UID
\-
discovering the owner of a user namespace
.SH SYNOPSIS
.nf
.BR "#include <linux/nsfs.h>" "  /* Definition of " NS_GET_OWNER_UID " */"
.B #include <sys/ioctl.h>
.P
.BI "int ioctl(int " fd ", NS_GET_OWNER_UID, uid_t *" uid );
.fi
.SH DESCRIPTION
The
.B NS_GET_OWNER_UID
operation can be used to discover
the owner user ID of a user namespace (i.e., the effective user ID
of the process that created the user namespace).
.P
.I fd
refers to a
.IR /proc/ pid /ns/user
file.
.P
The owner user ID is returned in the
.I uid_t
pointed to by the third argument.
.SH RETURN VALUE
On success,
0 is returned.
On error,
\-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I fd
does not refer to a user namespace.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 4.11.
.\" linux.git 015bb305b8ebe8d601a238ab70ebdc394c7a19ba
.SH SEE ALSO
.BR ioctl (2),
.BR ioctl_nsfs (2)