mirror of https://github.com/mkerrisk/man-pages
424 lines
12 KiB
Groff
424 lines
12 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu>
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.\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl>
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.\" and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2001-10-13 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added note on historical behavior of MS_NOSUID
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.\" Modified 2002-05-16 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Extensive changes and additions
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.\" Modified 2002-05-27 by aeb
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.\" Modified 2002-06-11 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT
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.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups.
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.\" 2008-10-06, mtk: move umount*() material into separate umount.2 page.
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.\" 2008-10-06, mtk: Add discussion of namespaces.
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.\"
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.TH MOUNT 2 2008-10-06 "Linux" "Linux Programmer's Manual"
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.SH NAME
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mount \- mount file system
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.SH SYNOPSIS
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.nf
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.B "#include <sys/mount.h>"
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.sp
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.BI "int mount(const char *" source ", const char *" target ,
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.BI " const char *" filesystemtype ", unsigned long " mountflags ,
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.BI " const void *" data );
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.fi
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.SH DESCRIPTION
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.BR mount ()
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attaches the file system specified by
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.I source
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(which is often a device name, but can also be a directory name
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or a dummy) to the directory specified by
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.IR target .
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Appropriate privilege (Linux: the
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.B CAP_SYS_ADMIN
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capability) is required to mount file systems.
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Since Linux 2.4 a single file system can be visible at
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multiple mount points, and multiple mounts can be stacked
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on the same mount point.
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.\" Multiple mounts on same mount point: since 2.3.99pre7.
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Values for the
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.I filesystemtype
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argument supported by the kernel are listed in
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.I /proc/filesystems
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(like "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
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"msdos", "proc", "nfs", "iso9660" etc.).
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Further types may become available when the appropriate modules
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are loaded.
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The
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.I mountflags
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argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP)
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in the top 16 bits (this was required in kernel versions prior to 2.4, but
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is no longer required and ignored if specified),
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and various mount flags (as defined in \fI<linux/fs.h>\fP for libc4 and libc5
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and in \fI<sys/mount.h>\fP for glibc2) in the low order 16 bits:
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.\" FIXME 2.6.15 added flags for "shared sub-tree" functionality:
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.\" MS_UNBINDABLE, MS_PRIVATE, MS_SHARED, MS_SLAVE
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.\" These need to be documented on this page.
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.\" See:
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.\" Documentation/filesystems/sharedsubtree.txt
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.\"
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.\" http://lwn.net/Articles/159077/
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.\"
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.\" http://myweb.sudhaa.com:2022/~ram/sharedsubtree/paper/sharedsubtree.1.pdf
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.\" Shared-Subtree Concept, Implementation, and Applications in Linux
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.\" Al Viro viro@ftp.linux.org.uk
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.\" Ram Pai linuxram@us.ibm.com
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.\"
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.\" http://foss.in/2005/slides/sharedsubtree1.pdf
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.\" Shared Subtree Concept and Implementation in the Linux Kernel
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.\" Ram Pai
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.\"
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.TP
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.BR MS_BIND " (Linux 2.4 onwards)"
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.\" since 2.4.0-test9
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Perform a bind mount, making a file or a directory subtree visible at
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another point within a file system.
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Bind mounts may cross file system boundaries and span
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.BR chroot (2)
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jails.
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The
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.IR filesystemtype
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and
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.IR data
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arguments are ignored.
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Up until Linux 2.6.26,
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.I mountflags
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was also ignored
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.\" with the exception of the "hidden" MS_REC mountflags bit
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(the bind mount has the same mount options as
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the underlying mount point).
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Since Linux 2.6.26, the
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.B MS_RDONLY
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flag is honored when making a bind mount.
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.TP
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.BR MS_DIRSYNC " (since Linux 2.5.19)"
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Make directory changes on this file system synchronous.
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(This property can be obtained for individual directories
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or subtrees using
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.BR chattr (1).)
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.TP
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.B MS_MANDLOCK
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Permit mandatory locking on files in this file system.
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(Mandatory locking must still be enabled on a per-file basis,
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as described in
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.BR fcntl (2).)
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.\" FIXME Say more about MS_MOVE
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.TP
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.B MS_MOVE
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Move a subtree.
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.I source
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specifies an existing mount point and
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.I target
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specifies the new location.
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The move is atomic: at no point is the subtree unmounted.
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The
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.IR filesystemtype ", " mountflags ", and " data
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arguments are ignored.
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.TP
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.B MS_NOATIME
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Do not update access times for (all types of) files on this file system.
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.TP
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.B MS_NODEV
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Do not allow access to devices (special files) on this file system.
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.TP
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.B MS_NODIRATIME
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Do not update access times for directories on this file system.
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This flag provides a subset of the functionality provided by
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.BR MS_NOATIME ;
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that is,
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.BR MS_NOATIME
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implies
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.BR MS_NODIRATIME .
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.TP
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.B MS_NOEXEC
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Do not allow programs to be executed from this file system.
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.\" (Possibly useful for a file system that contains non-Linux executables.
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.\" Often used as a security feature, e.g., to make sure that restricted
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.\" users cannot execute files uploaded using ftp or so.)
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.TP
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.B MS_NOSUID
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Do not honor set-user-ID and set-group-ID bits when executing
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programs from this file system.
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.\" (This is a security feature to prevent users executing set-user-ID and
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.\" set-group-ID programs from removable disk devices.)
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.TP
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.B MS_RDONLY
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Mount file system read-only.
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.\"
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.\" FIXME Document MS_REC, available since 2.4.11.
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.\" This flag has meaning in conjunction with MS_BIND and
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.\" also with the shared sub-tree flags.
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.TP
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.BR MS_RELATIME " (Since Linux 2.6.20)"
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When a file on this file system is accessed,
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only update the file's last access time (atime) if the current value
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of atime is less than or equal to the file's last modification time (mtime)
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or last status change time (ctime).
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This option is useful for programs, such as
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.BR mutt (1),
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that need to know when a file has been read since it was last modified.
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.TP
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.B MS_REMOUNT
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Remount an existing mount.
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This allows you to change the
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.I mountflags
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and
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.I data
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of an existing mount without having to unmount and remount the file system.
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.I source
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and
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.I target
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should be the same values specified in the initial
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.BR mount ()
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call;
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.I filesystemtype
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is ignored.
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The following
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.I mountflags
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can be changed:
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.BR MS_RDONLY ,
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.BR MS_SYNCHRONOUS ,
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.BR MS_MANDLOCK ;
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before kernel 2.6.16, the following could also be changed:
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.B MS_NOATIME
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and
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.BR MS_NODIRATIME ;
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and, additionally, before kernel 2.4.10, the following could also be changed:
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.BR MS_NOSUID ,
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.BR MS_NODEV ,
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.BR MS_NOEXEC .
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.TP
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.BR MS_SILENT " (since Linux 2.6.17)"
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Suppress the display of certain
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.RI ( printk ())
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warning messages in the kernel log.
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This flag supersedes the misnamed and obsolete
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.BR MS_VERBOSE
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flag (available since Linux 2.4.12), which has the same meaning.
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.TP
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.B MS_SYNCHRONOUS
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Make writes on this file system synchronous (as though
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the
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.B O_SYNC
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flag to
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.BR open (2)
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was specified for all file opens to this file system).
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.PP
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From Linux 2.4 onwards, the
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.BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
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flags are settable on a per-mount-point basis.
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From kernel 2.6.16 onwards,
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.B MS_NOATIME
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and
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.B MS_NODIRATIME
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are also settable on a per-mount-point basis.
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The
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.B MS_RELATIME
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flag is also settable on a per-mount-point basis.
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.PP
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The
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.I data
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argument is interpreted by the different file systems.
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Typically it is a string of comma-separated options
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understood by this file system.
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See
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.BR mount (8)
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for details of the options available for each filesystem type.
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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The error values given below result from filesystem type independent
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errors.
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Each filesystem type may have its own special errors and its
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own special behavior.
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See the kernel source code for details.
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.TP
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.B EACCES
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A component of a path was not searchable.
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(See also
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.BR path_resolution (7).)
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Or, mounting a read-only filesystem was attempted without giving the
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.B MS_RDONLY
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flag.
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Or, the block device
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.I source
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is located on a filesystem mounted with the
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.B MS_NODEV
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option.
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.\" mtk: Probably: write permission is required for MS_BIND, with
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.\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
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.TP
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.B EBUSY
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.I source
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is already mounted.
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Or, it cannot be remounted read-only,
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because it still holds files open for writing.
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Or, it cannot be mounted on
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.I target
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because
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.I target
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is still busy (it is the working directory of some task,
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the mount point of another device, has open files, etc.).
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.TP
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.B EFAULT
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One of the pointer arguments points outside the user address space.
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.TP
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.B EINVAL
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.I source
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had an invalid superblock.
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Or, a remount
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.RB ( MS_REMOUNT )
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was attempted, but
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.I source
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was not already mounted on
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.IR target .
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Or, a move
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.RB ( MS_MOVE )
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was attempted, but
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.I source
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was not a mount point, or was \(aq/\(aq.
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.TP
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.B ELOOP
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Too many links encountered during pathname resolution.
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Or, a move was attempted, while
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.I target
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is a descendant of
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.IR source .
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.TP
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.B EMFILE
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(In case no block device is required:)
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Table of dummy devices is full.
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.TP
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.B ENAMETOOLONG
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A pathname was longer than
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.BR MAXPATHLEN .
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.TP
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.B ENODEV
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.I filesystemtype
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not configured in the kernel.
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.TP
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.B ENOENT
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A pathname was empty or had a nonexistent component.
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.TP
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.B ENOMEM
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The kernel could not allocate a free page to copy filenames or data into.
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.TP
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.B ENOTBLK
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.I source
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is not a block device (and a device was required).
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.TP
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.B ENOTDIR
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.IR target ,
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or a prefix of
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.IR source ,
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is not a directory.
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.TP
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.B ENXIO
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The major number of the block device
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.I source
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is out of range.
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.TP
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.B EPERM
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The caller does not have the required privileges.
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.SH "CONFORMING TO"
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This function is Linux-specific and should not be used in
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programs intended to be portable.
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.SH NOTES
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The original
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.B MS_SYNC
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flag was renamed
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.B MS_SYNCHRONOUS
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in 1.1.69
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when a different
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.B MS_SYNC
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was added to \fI<mman.h>\fP.
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.LP
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Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
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on a filesystem mounted with
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.B MS_NOSUID
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would fail with
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.BR EPERM .
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Since Linux 2.4 the set-user-ID and set-group-ID bits are
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just silently ignored in this case.
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.\" The change is in patch-2.4.0-prerelease.
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.SS Per-process Namespaces
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Starting with kernel 2.4.19, Linux provides per-process namespaces.
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A namespace is the set of file system mounts that are visible to a process.
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Namespaces can be (and usually are) shared between multiple processes,
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and changes to the namespace (i.e., mounts and unmounts) by one process
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are visible to all other processes sharing the same namespace.
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(The pre-2.4.19 Linux situation can be considered as one in which there
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was a single namespace was shared by every process on the system.)
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A child process created by
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.BR fork (2)
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shares its parent's namespace;
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the namespace is preserved across an
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.BR execve (2).
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A process can obtain a private namespace if:
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it was created using the
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.BR clone ()
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.BR CLONE_NEWNS
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flag,
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in which case its new namespace is initialized to be a
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.I copy
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of the namespace of the process that called
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.BR clone ();
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or it calls
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.BR unshare (2)
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with the
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.BR CLONE_NEWNS
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flag,
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which causes the caller's namespace to obtain a private copy
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of the namespace that it was previously sharing with other processes,
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so that future mounts and unmounts by the caller are invisible
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to other processes (except child processes that the caller
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subsequently creates) and vice versa.
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The Linux-specific
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.I /proc/PID/self
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file exposes the list of mount points in the namespace of the process with
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the specified ID; see
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.BR proc (5)
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for details.
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.SH "SEE ALSO"
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.BR umount (2),
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.BR path_resolution (7),
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.BR mount (8),
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.BR umount (8)
|