-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" Copyright (C) 1993 Rickard E. Faith <faith@cs.unc.edu>
.\" and Copyright (C) 1994 Andries E. Brouwer <aeb@cwi.nl>
.\" and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2001-10-13 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" 2008-10-06, mtk: move umount*() material into separate umount.2 page.
.\" 2008-10-06, mtk: Add discussion of namespaces.
.\"
-.TH MOUNT 2 2010-05-22 "Linux" "Linux Programmer's Manual"
+.TH MOUNT 2 2016-03-15 "Linux" "Linux Programmer's Manual"
.SH NAME
-mount \- mount file system
+mount \- mount filesystem
.SH SYNOPSIS
.nf
.B "#include <sys/mount.h>"
.fi
.SH DESCRIPTION
.BR mount ()
-attaches the file system specified by
+attaches the filesystem specified by
.I source
(which is often a device name, but can also be a directory name
or a dummy) to the directory specified by
Appropriate privilege (Linux: the
.B CAP_SYS_ADMIN
-capability) is required to mount file systems.
+capability) is required to mount filesystems.
-Since Linux 2.4 a single file system can be visible at
+Since Linux 2.4 a single filesystem can be visible at
multiple mount points, and multiple mounts can be stacked
on the same mount point.
.\" Multiple mounts on same mount point: since 2.3.99pre7.
.I filesystemtype
argument supported by the kernel are listed in
.I /proc/filesystems
-(like "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
-"msdos", "proc", "nfs", "iso9660" etc.).
+(e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
+"msdos", "proc", "nfs", "iso9660").
Further types may become available when the appropriate modules
are loaded.
argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP)
in the top 16 bits (this was required in kernel versions prior to 2.4, but
is no longer required and ignored if specified),
-and various mount flags (as defined in \fI<linux/fs.h>\fP for libc4 and libc5
-and in \fI<sys/mount.h>\fP for glibc2) in the low order 16 bits:
+and various mount flags
+.\" (as defined in \fI<linux/fs.h>\fP for libc4 and libc5
+.\" and in \fI<sys/mount.h>\fP for glibc2)
+in the low order 16 bits:
.\" FIXME 2.6.15 added flags for "shared subtree" functionality:
-.\" MS_UNBINDABLE, MS_PRIVATE, MS_SHARED, MS_SLAVE
+.\"
+.\" MS_PRIVATE
+.\" All mounts are private by default. Previously shared mounts
+.\" can be re-marked PRIVATE.
+.\" MS_SHARED
+.\" Mount points that are marked SHARED propagate mount events
+.\" to one another after being cloned.
+.\" mount --make-rshared ==> MS_SHARED | MS_REC
+.\" MS_SLAVE
+.\" A previously shared mount point can be marked SLAVE, meaning
+.\" it receives propagated events, but does not propagate events.
+.\" MS_UNBINDABLE
+.\" mounts cannot be bound into other places, and will not be
+.\" propagated into new subtrees
+.\"
+.\" These settings are visible in /proc/$$/mountinfo
+.\"
.\" These need to be documented on this page.
.\" See:
-.\" Documentation/filesystems/sharedsubtree.txt
.\"
-.\" http://lwn.net/Articles/159077/
+.\" * Documentation/filesystems/sharedsubtree.txt
+.\"
+.\" * http://lwn.net/Articles/159077/
+.\"
+.\" * https://www.kernel.org/doc/ols/2006/ols2006v2-pages-209-222.pdf
+.\" Shared-Subtree Concept, Implementation, and Applications in Linux
+.\" Al Viro viro@ftp.linux.org.uk
+.\" Ram Pai linuxram@us.ibm.com
.\"
-.\" http://myweb.sudhaa.com:2022/~ram/sharedsubtree/paper/sharedsubtree.1.pdf
-.\" Shared-Subtree Concept, Implementation, and Applications in Linux
-.\" Al Viro viro@ftp.linux.org.uk
-.\" Ram Pai linuxram@us.ibm.com
+.\" * http://www.ibm.com/developerworks/linux/library/l-mount-namespaces/index.html
+.\" Applying mount namespaces
.\"
-.\" http://foss.in/2005/slides/sharedsubtree1.pdf
-.\" Shared Subtree Concept and Implementation in the Linux Kernel
-.\" Ram Pai
+.\" Uncover practical applications for advanced Linux mounts features
+.\" Serge E. Hallyn (sergeh@us.ibm.com), Software Engineer, IBM
+.\" Ram Pai (linuxram@us.ibm.com), Software Engineer, IBM
+.\" Date: 17 Sep 2007
.\"
-.\" 2.6.25 Added MS_I_VERSION, which needs to be documented.
+.\" FIXME 2.6.25 Added MS_I_VERSION, which needs to be documented.
.\"
.TP
-.BR MS_BIND " (Linux 2.4 onwards)"
+.BR MS_BIND " (Linux 2.4 onward)"
.\" since 2.4.0-test9
Perform a bind mount, making a file or a directory subtree visible at
-another point within a file system.
-Bind mounts may cross file system boundaries and span
+another point within a filesystem.
+Bind mounts may cross filesystem boundaries and span
.BR chroot (2)
jails.
The
.\" with the exception of the "hidden" MS_REC mountflags bit
(the bind mount has the same mount options as
the underlying mount point).
-Since Linux 2.6.26, the
-.B MS_RDONLY
-flag is honored when making a bind mount.
.TP
.BR MS_DIRSYNC " (since Linux 2.5.19)"
-Make directory changes on this file system synchronous.
+Make directory changes on this filesystem synchronous.
(This property can be obtained for individual directories
or subtrees using
.BR chattr (1).)
.TP
+.BR MS_LAZYTIME " (since Linux 4.0)"
+.\" commit 0ae45f63d4ef8d8eeec49c7d8b44a1775fff13e8
+.\" commit fe032c422c5ba562ba9c2d316f55e258e03259c6
+.\" commit a26f49926da938f47561f386be56a83dd37a496d
+Reduce on-disk updates of inode timestamps (atime, mtime, ctime)
+by maintaining these changes only in memory.
+The on-disk timestamps are updated only when:
+.RS
+.IP (a) 5
+the inode needs to be updated for some change unrelated to file timestamps;
+.IP (b)
+the application employs
+.BR fsync (2),
+.BR syncfs (2),
+or
+.BR sync (2);
+.IP (c)
+an undeleted inode is evicted from memory; or
+.IP (d)
+more than 24 hours have passed since the inode was written to disk.
+.RE
+.IP
+This mount option significantly reduces writes
+needed to update the inode's timestamps, especially mtime and atime.
+However, in the event of a system crash, the atime and mtime fields
+on disk might be out of date by up to 24 hours.
+
+Examples of workloads where this option could be of significant benefit
+include frequent random writes to preallocated files,
+as well as cases where the
+.B MS_STRICTATIME
+mount option is also enabled.
+(The advantage of combining
+.BR MS_STRICTATIME
+and
+.BR MS_LAZYTIME
+is that
+.BR stat (2)
+will return the correctly updated atime, but the atime updates
+will be flushed to disk only in the cases listed above.)
+.TP
.B MS_MANDLOCK
-Permit mandatory locking on files in this file system.
+Permit mandatory locking on files in this filesystem.
(Mandatory locking must still be enabled on a per-file basis,
as described in
.BR fcntl (2).)
-.\" FIXME Say more about MS_MOVE
+.\" FIXME Describe the MS_MOVE flag in more detail
.TP
.B MS_MOVE
Move a subtree.
arguments are ignored.
.TP
.B MS_NOATIME
-Do not update access times for (all types of) files on this file system.
+Do not update access times for (all types of) files on this filesystem.
.TP
.B MS_NODEV
-Do not allow access to devices (special files) on this file system.
+Do not allow access to devices (special files) on this filesystem.
.TP
.B MS_NODIRATIME
-Do not update access times for directories on this file system.
+Do not update access times for directories on this filesystem.
This flag provides a subset of the functionality provided by
.BR MS_NOATIME ;
that is,
.BR MS_NODIRATIME .
.TP
.B MS_NOEXEC
-Do not allow programs to be executed from this file system.
-.\" (Possibly useful for a file system that contains non-Linux executables.
+Do not allow programs to be executed from this filesystem.
+.\" (Possibly useful for a filesystem that contains non-Linux executables.
.\" Often used as a security feature, e.g., to make sure that restricted
.\" users cannot execute files uploaded using ftp or so.)
.TP
.B MS_NOSUID
Do not honor set-user-ID and set-group-ID bits when executing
-programs from this file system.
+programs from this filesystem.
.\" (This is a security feature to prevent users executing set-user-ID and
.\" set-group-ID programs from removable disk devices.)
.TP
.B MS_RDONLY
-Mount file system read-only.
+Mount filesystem read-only.
.\"
.\" FIXME Document MS_REC, available since 2.4.11.
.\" This flag has meaning in conjunction with MS_BIND and
.\" also with the shared subtree flags.
.TP
-.BR MS_RELATIME " (Since Linux 2.6.20)"
-When a file on this file system is accessed,
-only update the file's last access time (atime) if the current value
+.BR MS_RELATIME " (since Linux 2.6.20)"
+When a file on this filesystem is accessed,
+update the file's last access time (atime) only if the current value
of atime is less than or equal to the file's last modification time (mtime)
or last status change time (ctime).
This option is useful for programs, such as
is more than 1 day old.
.\" Matthew Garrett notes in the patch that added this behavior
.\" that this lets utilities such as tmpreaper (which deletes
-.\" files based on last acces time) work correctly.
+.\" files based on last access time) work correctly.
.TP
.B MS_REMOUNT
Remount an existing mount.
.I mountflags
and
.I data
-of an existing mount without having to unmount and remount the file system.
-.I source
-and
+of an existing mount without having to unmount and remount the filesystem.
.I target
-should be the same values specified in the initial
+should be the same value specified in the initial
.BR mount ()
call;
+.I source
+and
.I filesystemtype
-is ignored.
+are ignored.
+The
+.I mountflags
+and
+.I data
+arguments should match the values used in the original
+.BR mount ()
+call, except for those parameters that are being deliberately changed.
The following
.I mountflags
.BR MS_VERBOSE
flag (available since Linux 2.4.12), which has the same meaning.
.TP
-.BR MS_STRICTATIME " (Since Linux 2.6.30)"
+.BR MS_STRICTATIME " (since Linux 2.6.30)"
Always update the last access time (atime) when files on this
-file system are accessed.
+filesystem are accessed.
(This was the default behavior before Linux 2.6.30.)
Specifying this flag overrides the effect of setting the
.BR MS_NOATIME
flags.
.TP
.B MS_SYNCHRONOUS
-Make writes on this file system synchronous (as though
+Make writes on this filesystem synchronous (as though
the
.B O_SYNC
flag to
.BR open (2)
-was specified for all file opens to this file system).
+was specified for all file opens to this filesystem).
.PP
-From Linux 2.4 onwards, the
+From Linux 2.4 onward, the
.BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
flags are settable on a per-mount-point basis.
-From kernel 2.6.16 onwards,
+From kernel 2.6.16 onward,
.B MS_NOATIME
and
.B MS_NODIRATIME
.PP
The
.I data
-argument is interpreted by the different file systems.
+argument is interpreted by the different filesystems.
Typically it is a string of comma-separated options
-understood by this file system.
+understood by this filesystem.
See
.BR mount (8)
for details of the options available for each filesystem type.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
errors.
Each filesystem type may have its own special errors and its
own special behavior.
-See the kernel source code for details.
+See the Linux kernel source code for details.
.TP
.B EACCES
A component of a path was not searchable.
.I target
because
.I target
-is still busy (it is the working directory of some task,
+is still busy (it is the working directory of some thread,
the mount point of another device, has open files, etc.).
.TP
.B EFAULT
.TP
.B EPERM
The caller does not have the required privileges.
-.SH "CONFORMING TO"
+.SH VERSIONS
+The definitions of
+.BR MS_DIRSYNC ,
+.BR MS_MOVE ,
+.BR MS_REC ,
+.BR MS_RELATIME ,
+and
+.BR MS_STRICTATIME
+were added to glibc headers in version 2.12.
+.\" FIXME . Definitions of the so-far-undocumented MS_UNBINDABLE, MS_PRIVATE,
+.\" MS_SHARED, and MS_SLAVE were (also) only added to glibc headers in 2.12.
+.SH CONFORMING TO
This function is Linux-specific and should not be used in
programs intended to be portable.
.SH NOTES
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
+.SS Per-process namespaces
Starting with kernel 2.4.19, Linux provides
per-process mount namespaces.
-A mount namespace is the set of file system mounts that
+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,
A process can obtain a private mount namespace if:
it was created using the
-.BR clone ()
+.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 ();
+.BR clone (2);
or it calls
.BR unshare (2)
with the
namespace of the process with the specified ID; see
.BR proc (5)
for details.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR umount (2),
+.BR namespaces (7),
.BR path_resolution (7),
+.BR lsblk (8),
+.BR findmnt (8),
.BR mount (8),
.BR umount (8)
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