mirror of https://github.com/mkerrisk/man-pages
534 lines
16 KiB
Groff
534 lines
16 KiB
Groff
.\" 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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.\" %%%LICENSE_START(VERBATIM)
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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.\" manual page may be incorrect or out-of-date.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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.\" %%%LICENSE_END
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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 2015-04-19 "Linux" "Linux Programmer's Manual"
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.SH NAME
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mount \- mount filesystem
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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 filesystem 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 filesystems.
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Since Linux 2.4 a single filesystem 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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(e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
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"msdos", "proc", "nfs", "iso9660").
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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
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.\" (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)
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in the low order 16 bits:
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.\" FIXME 2.6.15 added flags for "shared subtree" functionality:
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.\"
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.\" MS_PRIVATE
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.\" All mounts are private by default. Previously shared mounts
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.\" can be re-marked PRIVATE.
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.\" MS_SHARED
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.\" Mount points that are marked SHARED propagate mount events
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.\" to one another after bieing cloned.
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.\" mount --make-rshared ==> MS_SHARED | MS_REC
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.\" MS_SLAVE
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.\" A previously shared mount point can be marked SLAVE, meaning
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.\" it receives propagated events, but does not propagate events.
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.\" MS_UNBINDABLE
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.\" mounts cannot be bound into other places, and will not be
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.\" propagated into new subtrees
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.\"
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.\" These settings are visible in /proc/$$/mountinfo
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.\"
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.\" These need to be documented on this page.
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.\" See:
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.\"
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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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.\" * https://www.kernel.org/doc/ols/2006/ols2006v2-pages-209-222.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://www.ibm.com/developerworks/linux/library/l-mount-namespaces/index.html
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.\" Applying mount namespaces
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.\"
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.\" Uncover practical applications for advanced Linux mounts features
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.\" Serge E. Hallyn (sergeh@us.ibm.com), Software Engineer, IBM
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.\" Ram Pai (linuxram@us.ibm.com), Software Engineer, IBM
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.\" Date: 17 Sep 2007
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.\"
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.\" FIXME 2.6.25 Added MS_I_VERSION, which needs to be documented.
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.\"
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.TP
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.BR MS_BIND " (Linux 2.4 onward)"
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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 filesystem.
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Bind mounts may cross filesystem 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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.TP
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.BR MS_DIRSYNC " (since Linux 2.5.19)"
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Make directory changes on this filesystem 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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.BR MS_LAZYTIME " (since Linux 4.0)"
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.\" commit 0ae45f63d4ef8d8eeec49c7d8b44a1775fff13e8
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.\" commit fe032c422c5ba562ba9c2d316f55e258e03259c6
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.\" commit a26f49926da938f47561f386be56a83dd37a496d
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Reduce on-disk updates of inode timestamps (atime, mtime, ctime)
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by maintaining these changes only in memory.
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The on-disk timestamps are updated only when:
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.RS
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.IP (a) 5
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the inode needs to be updated for some change unrelated to file timestamps;
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.IP (b)
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the application employs
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.BR fsync (2),
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.BR syncfs (2),
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or
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.BR sync (2);
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.IP (c)
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an undeleted inode is evicted from memory; or
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.IP (d)
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more than 24 hours have passed since the inode was written to disk.
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.RE
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.IP
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This mount option significantly reduces writes
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needed to update the inode's timestamps, especially mtime and atime.
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However, in the event of a system crash, the atime and mtime fields
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on disk might be out of date by up to 24 hours.
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Examples of workloads where this option could be of significant benefit
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include frequent random writes to preallocated files,
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as well as cases where the
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.B MS_STRICTATIME
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mount option is also enabled.
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(The advantage of combining
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.BR MS_STRICTATIME
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and
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.BR MS_LAZYTIME
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is that
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.BR stat (2)
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will return the correctly updated atime, but the atime updates
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will be flushed to disk only in the cases listed above.)
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.TP
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.B MS_MANDLOCK
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Permit mandatory locking on files in this filesystem.
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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 Describe the MS_MOVE flag in more detail
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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 filesystem.
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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 filesystem.
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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 filesystem.
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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 filesystem.
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.\" (Possibly useful for a filesystem 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 filesystem.
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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 filesystem 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 subtree 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 filesystem is accessed,
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update the file's last access time (atime) only 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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Since Linux 2.6.30, the kernel defaults to the behavior provided
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by this flag (unless
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.BR MS_NOATIME
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was specified), and the
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.B MS_STRICTATIME
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flag is required to obtain traditional semantics.
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In addition, since Linux 2.6.30,
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the file's last access time is always updated if it
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is more than 1 day old.
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.\" Matthew Garrett notes in the patch that added this behavior
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.\" that this lets utilities such as tmpreaper (which deletes
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.\" files based on last access time) work correctly.
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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 filesystem.
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.I target
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should be the same value specified in the initial
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.BR mount ()
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call;
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.I source
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and
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.I filesystemtype
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are ignored.
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The
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.I mountflags
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and
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.I data
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arguments should match the values used in the original
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.BR mount ()
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call, except for those parameters that are being deliberately changed.
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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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.BR MS_STRICTATIME " (since Linux 2.6.30)"
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Always update the last access time (atime) when files on this
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filesystem are accessed.
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(This was the default behavior before Linux 2.6.30.)
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Specifying this flag overrides the effect of setting the
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.BR MS_NOATIME
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and
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.BR MS_RELATIME
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flags.
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.TP
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.B MS_SYNCHRONOUS
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Make writes on this filesystem 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 filesystem).
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.PP
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From Linux 2.4 onward, 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 onward,
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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 filesystems.
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Typically it is a string of comma-separated options
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understood by this filesystem.
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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 Linux 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 thread,
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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.
|
|
.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).
|
|
.TP
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.B ENOTDIR
|
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.IR target ,
|
|
or a prefix of
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|
.IR source ,
|
|
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 VERSIONS
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|
The definitions of
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.BR MS_DIRSYNC ,
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.BR MS_MOVE ,
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.BR MS_REC ,
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.BR MS_RELATIME ,
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and
|
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.BR MS_STRICTATIME
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|
were added to glibc headers in version 2.12.
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|
.\" FIXME . Definitions of the so-far-undocumented MS_UNBINDABLE, MS_PRIVATE,
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.\" MS_SHARED, and MS_SLAVE were (also) only added to glibc headers in 2.12.
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.SH CONFORMING TO
|
|
This function is Linux-specific and should not be used in
|
|
programs intended to be portable.
|
|
.SH NOTES
|
|
The original
|
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.B MS_SYNC
|
|
flag was renamed
|
|
.B MS_SYNCHRONOUS
|
|
in 1.1.69
|
|
when a different
|
|
.B MS_SYNC
|
|
was added to \fI<mman.h>\fP.
|
|
.LP
|
|
Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
|
|
on a filesystem mounted with
|
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.B MS_NOSUID
|
|
would fail with
|
|
.BR EPERM .
|
|
Since Linux 2.4 the set-user-ID and set-group-ID bits are
|
|
just silently ignored in this case.
|
|
.\" The change is in patch-2.4.0-prerelease.
|
|
.SS Per-process namespaces
|
|
Starting with kernel 2.4.19, Linux provides
|
|
per-process mount namespaces.
|
|
A mount namespace is the set of filesystem mounts that
|
|
are visible to a process.
|
|
Mount-point namespaces can be (and usually are)
|
|
shared between multiple processes,
|
|
and changes to the namespace (i.e., mounts and unmounts) by one process
|
|
are visible to all other processes sharing the same namespace.
|
|
(The pre-2.4.19 Linux situation can be considered as one in which
|
|
a single namespace was shared by every process on the system.)
|
|
|
|
A child process created by
|
|
.BR fork (2)
|
|
shares its parent's mount namespace;
|
|
the mount namespace is preserved across an
|
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.BR execve (2).
|
|
|
|
A process can obtain a private mount namespace if:
|
|
it was created using the
|
|
.BR clone (2)
|
|
.BR CLONE_NEWNS
|
|
flag,
|
|
in which case its new namespace is initialized to be a
|
|
.I copy
|
|
of the namespace of the process that called
|
|
.BR clone (2);
|
|
or it calls
|
|
.BR unshare (2)
|
|
with the
|
|
.BR CLONE_NEWNS
|
|
flag,
|
|
which causes the caller's mount namespace to obtain a private copy
|
|
of the namespace that it was previously sharing with other processes,
|
|
so that future mounts and unmounts by the caller are invisible
|
|
to other processes (except child processes that the caller
|
|
subsequently creates) and vice versa.
|
|
|
|
The Linux-specific
|
|
.I /proc/PID/mounts
|
|
file exposes the list of mount points in the mount
|
|
namespace of the process with the specified ID; see
|
|
.BR proc (5)
|
|
for details.
|
|
.SH SEE ALSO
|
|
.BR umount (2),
|
|
.BR namespaces (7),
|
|
.BR path_resolution (7),
|
|
.BR lsblk (8),
|
|
.BR mount (8),
|
|
.BR umount (8)
|