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+.\" Copyright 2017, Michael Kerrisk <mtk.manpages@gmail.com>
+.\" Copyright 2024, Alejandro Colomar <alx@kernel.org>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH ioctl_nsfs 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+ioctl_nsfs
+\-
+ioctl() operations for Linux namespaces
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/nsfs.h>" "  /* Definition of " NS_* " constants */"
+.B #include <sys/ioctl.h>
+.P
+.BI "int ioctl(int " fd ", unsigned long " op ", ...);"
+.fi
+.SH DESCRIPTION
+.SS Discovering namespace relationships
+.TP
+.B NS_GET_USERNS
+.TQ
+.B NS_GET_PARENT
+.SS Discovering the namespace type
+.TP
+.B NS_GET_NSTYPE
+.SS Discovering the owner of a user namespace
+.TP
+.B NS_GET_OWNER_UID
+.SH ERRORS
+.TP
+.B ENOTTY
+.I fd
+does not refer to a
+.IR /proc/ pid /ns/ *
+file.
+.SH STANDARDS
+Linux.
+.SH SEE ALSO
+.BR ioctl (2),
+.BR NS_GET_USERNS (2const),
+.BR NS_GET_PARENT (2const),
+.BR NS_GET_NSTYPE (2const),
+.BR NS_GET_OWNER_UID (2const),
+.BR fstat (2),
+.BR proc (5),
+.BR namespaces (7)