.\" 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>
+.\" and Copyright (C) 2002, 2005, 2016 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" 2008-10-06, mtk: move umount*() material into separate umount.2 page.
.\" 2008-10-06, mtk: Add discussion of namespaces.
.\"
-.TH MOUNT 2 2016-03-15 "Linux" "Linux Programmer's Manual"
+.TH MOUNT 2 2019-08-02 "Linux" "Linux Programmer's Manual"
.SH NAME
mount \- mount filesystem
.SH SYNOPSIS
.nf
.B "#include <sys/mount.h>"
-.sp
+.PP
.BI "int mount(const char *" source ", const char *" target ,
.BI " const char *" filesystemtype ", unsigned long " mountflags ,
.BI " const void *" data );
or a dummy string) to the location (a directory or file)
specified by the pathname in
.IR target .
-
+.PP
Appropriate privilege (Linux: the
.B CAP_SYS_ADMIN
capability) is required to mount filesystems.
-
-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.
-
+.PP
Values for the
.I filesystemtype
argument supported by the kernel are listed in
.I /proc/filesystems
-(e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
-"msdos", "proc", "nfs", "iso9660").
+(e.g., "btrfs", "ext4", "jfs", "xfs", "vfat", "fuse",
+"tmpfs", "cgroup", "proc", "mqueue", "nfs", "cifs", "iso9660").
Further types may become available when the appropriate modules
are loaded.
-
-The following flags may be specified in
-.IR mountflags :
-.\" FIXME 2.6.15 added flags for "shared subtree" functionality:
-.\"
-.\" 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/
-.\"
-.\" * 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://www.ibm.com/developerworks/linux/library/l-mount-namespaces/index.html
-.\" Applying mount namespaces
+.PP
+The
+.I data
+argument is interpreted by the different filesystems.
+Typically it is a string of comma-separated options
+understood by this filesystem.
+See
+.BR mount (8)
+for details of the options available for each filesystem type.
+.PP
+A call to
+.BR mount ()
+performs one of a number of general types of operation,
+depending on the bits specified in
+.IR mountflags .
+The choice of which operation to perform is determined by
+testing the bits set in
+.IR mountflags ,
+with the tests being conducted in the order listed here:
+.IP * 3
+Remount an existing mount:
+.IR mountflags
+includes
+.BR MS_REMOUNT .
+.IP *
+Create a bind mount:
+.IR mountflags
+includes
+.BR MS_BIND .
+.IP *
+Change the propagation type of an existing mount:
+.IR mountflags
+includes one of
+.BR MS_SHARED ,
+.BR MS_PRIVATE ,
+.BR MS_SLAVE ,
+or
+.BR MS_UNBINDABLE .
+.IP *
+Move an existing mount to a new location:
+.IR mountflags
+includes
+.BR MS_MOVE .
+.IP *
+Create a new mount:
+.IR mountflags
+includes none of the above flags.
+.PP
+Each of these operations is detailed later in this page.
+Further flags may be specified in
+.IR mountflags
+to modify the behavior of
+.BR mount (),
+as described below.
.\"
-.\" 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
+.SS Additional mount flags
+The list below describes the additional flags that can be specified in
+.IR mountflags .
+Note that some operation types ignore some or all of these flags,
+as described later in this page.
.\"
.\" FIXME 2.6.25 Added MS_I_VERSION, which needs to be documented.
+.\" commit 7a224228ed79d587ece2304869000aad1b8e97dd
+.\" (This is a per-superblock flag)
.\"
.TP
-.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 filesystem.
-Bind mounts may cross filesystem boundaries and span
-.BR chroot (2)
-jails.
-The
-.IR filesystemtype
-and
-.IR data
-arguments are ignored.
-The remaining bits in the
-.I mountflags
-argument are also ignored, with the exception of
-.B MS_REC
-(the bind mount has the same mount options as
-the underlying mount point).
-.TP
.BR MS_DIRSYNC " (since Linux 2.5.19)"
Make directory changes on this filesystem synchronous.
(This property can be obtained for individual directories
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.
-
+.IP
Examples of workloads where this option could be of significant benefit
include frequent random writes to preallocated files,
as well as cases where the
.\" commit 95ace75414f312f9a7b93d873f386987b92a5301
this mount option requires the
.B CAP_SYS_ADMIN
-capability.
-.\" FIXME Describe the MS_MOVE flag in more detail
-.TP
-.B MS_MOVE
-Move a subtree.
-.I source
-specifies an existing mount point and
-.I target
-specifies the new location.
-The move is atomic: at no point is the subtree unmounted.
-The remaining bits in the
-.IR mountflags
-argument are ignored, as are the
-.IR filesystemtype
-and
-.IR data
-arguments.
+capability and a kernel configured with the
+.B CONFIG_MANDATORY_FILE_LOCKING
+option.
.TP
.B MS_NOATIME
Do not update access times for (all types of) files on this filesystem.
.TP
.B MS_RDONLY
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_REC " (since Linux 2.4.11)"
+Used in conjunction with
+.BR MS_BIND
+to create a recursive bind mount,
+and in conjunction with the propagation type flags to recursively change
+the propagation type of all of the mounts in a subtree.
+See below for further details.
.TP
.BR MS_RELATIME " (since Linux 2.6.20)"
When a file on this filesystem is accessed,
.\" that this lets utilities such as tmpreaper (which deletes
.\" files based on last access time) work correctly.
.TP
+.BR MS_SILENT " (since Linux 2.6.17)"
+Suppress the display of certain
+.RI ( printk ())
+warning messages in the kernel log.
+This flag supersedes the misnamed and obsolete
+.BR MS_VERBOSE
+flag (available since Linux 2.4.12), which has the same meaning.
+.TP
+.BR MS_STRICTATIME " (since Linux 2.6.30)"
+Always update the last access time (atime) when files on this
+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
+and
+.BR MS_RELATIME
+flags.
+.TP
+.B MS_SYNCHRONOUS
+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 filesystem).
+.PP
+From Linux 2.4 onward, some of the above flags are
+settable on a per-mount basis,
+while others apply to the superblock of the mounted filesystem,
+meaning that all mounts of the same filesystem share those flags.
+(Previously, all of the flags were per-superblock.)
+.PP
+The per-mount-point flags are as follows:
+.IP * 3
+Since Linux 2.4:
+.BR MS_NODEV ", " MS_NOEXEC ", and " MS_NOSUID
+flags are settable on a per-mount-point basis.
+.IP *
+Since Linux 2.6.16:
+.B MS_NOATIME
+and
+.BR MS_NODIRATIME .
+.IP *
+Since Linux 2.6.20:
+.BR MS_RELATIME .
+.PP
+The following flags are per-superblock:
+.BR MS_DIRSYNC ,
+.BR MS_LAZYTIME ,
+.BR MS_MANDLOCK ,
+.BR MS_MS_SILENT ,
+and
+.BR MS_SYNCHRONOUS .
+.\" And MS_I_VERSION?
+The initial settings of these flags are determined on the first
+mount of the filesystem, and will be shared by all subsequent mounts
+of the same filesystem.
+Subsequently, the settings of the flags can be changed
+via a remount operation (see below).
+Such changes will be visible via all mount points associated
+with the filesystem.
+.PP
+Since Linux 2.6.16,
+.B MS_RDONLY
+can be set or cleared on a per-mount-point basis as well as on
+the underlying filesystem superblock.
+The mounted filesystem will be writable only if neither the filesystem
+nor the mountpoint are flagged as read-only.
+.\"
+.SS Remounting an existing mount
+An existing mount may be remounted by specifying
.B MS_REMOUNT
-Remount an existing mount.
+in
+.IR mountflags .
This allows you to change the
.I mountflags
and
.I target
should be the same value specified in the initial
.BR mount ()
-call;
+call.
+.PP
+The
.I source
and
.I filesystemtype
-are ignored.
+arguments are ignored.
+.PP
The
.I mountflags
and
arguments should match the values used in the original
.BR mount ()
call, except for those parameters that are being deliberately changed.
-
+.PP
The following
.I mountflags
can be changed:
+.BR MS_LAZYTIME ,
+.\" FIXME
+.\" MS_LAZYTIME seems to be available only on a few filesystems,
+.\" and on ext4, it seems (from experiment that this flag
+.\" can only be enabled (but not disabled) on a remount.
+.\" The following code in ext4_remount() (kernel 4.17) seems to
+.\" confirm this:
+.\"
+.\" if (*flags & SB_LAZYTIME)
+.\" sb->s_flags |= SB_LAZYTIME;
+.BR MS_MANDLOCK ,
+.BR MS_NOATIME ,
+.BR MS_NODEV ,
+.BR MS_NODIRATIME ,
+.BR MS_NOEXEC ,
+.BR MS_NOSUID ,
+.BR MS_RELATIME ,
.BR MS_RDONLY ,
-.BR MS_SYNCHRONOUS ,
+.BR MS_STRICTATIME
+(whose effect is to clear the
+.BR MS_NOATIME
and
-.BR MS_MANDLOCK ;
-before kernel 2.6.16, the following could also be changed:
-.B MS_NOATIME
+.BR MS_RELATIME
+flags),
and
-.BR MS_NODIRATIME ;
-and, additionally, before kernel 2.4.10, the following could also be changed:
-.BR MS_NOSUID ,
-.BR MS_NODEV ,
+.BR MS_SYNCHRONOUS .
+Attempts to change the setting of the
+.\" See the definition of MS_RMT_MASK in include/uapi/linux/fs.h,
+.\" which excludes MS_DIRSYNC and MS_SILENT, although SB_DIRSYNC
+.\" and SB_SILENT are split out as per-superblock flags in do_mount()
+.\" (Linux 4.17 source code)
+.BR MS_DIRSYNC
and
-.BR MS_NOEXEC .
-
+.BR MS_SILENT
+flags during a remount are silently ignored.
+Note that changes to per-superblock flags are visible via
+all mount points of the associated filesystem
+(because the per-superblock flags are shared by all mount points).
+.PP
Since Linux 3.17,
.\" commit ffbc6f0ead47fa5a1dc9642b0331cb75c20a640e
if none of
then the remount operation preserves the existing values of these flags
(rather than defaulting to
.BR MS_RELATIME ).
-
-Since Linux 2.6.26, this flag can also be used to make
+.PP
+Since Linux 2.6.26, the
+.B MS_REMOUNT
+flag can be used with
+.B MS_BIND
+to modify only the per-mount-point flags.
.\" See https://lwn.net/Articles/281157/
-an existing bind mount read-only by specifying
+This is particularly useful for setting or clearing the "read-only"
+flag on a mount point without changing the underlying filesystem.
+Specifying
.IR mountflags
as:
-
- MS_REMOUNT | MS_BIND | MS_RDONLY
-
-Note that only the
-.BR MS_RDONLY
-setting of the bind mount can be changed in this manner.
+.PP
+.in +4n
+.EX
+MS_REMOUNT | MS_BIND | MS_RDONLY
+.EE
+.in
+.PP
+will make access through this mountpoint read-only, without affecting
+other mount points.
+.\"
+.SS Creating a bind mount
+If
+.I mountflags
+includes
+.BR MS_BIND
+(available since Linux 2.4),
+.\" since 2.4.0-test9
+then perform a bind mount.
+A bind mount makes a file or a directory subtree visible at
+another point within the single directory hierarchy.
+Bind mounts may cross filesystem boundaries and span
+.BR chroot (2)
+jails.
+.PP
+The
+.IR filesystemtype
+and
+.IR data
+arguments are ignored.
+.PP
+The remaining bits (other than
+.BR MS_REC ,
+described below) in the
+.I mountflags
+argument are also ignored.
+(The bind mount has the same mount options as
+the underlying mount point.)
+However, see the discussion of remounting above,
+for a method of making an existing bind mount read-only.
+.PP
+By default, when a directory is bind mounted,
+only that directory is mounted;
+if there are any submounts under the directory tree,
+they are not bind mounted.
+If the
+.BR MS_REC
+flag is also specified, then a recursive bind mount operation is performed:
+all submounts under the
+.I source
+subtree (other than unbindable mounts)
+are also bind mounted at the corresponding location in the
+.I target
+subtree.
+.\"
+.SS Changing the propagation type of an existing mount
+If
+.IR mountflags
+includes one of
+.BR MS_SHARED ,
+.BR MS_PRIVATE ,
+.BR MS_SLAVE ,
+or
+.BR MS_UNBINDABLE
+(all available since Linux 2.6.15),
+then the propagation type of an existing mount is changed.
+If more than one of these flags is specified, an error results.
+.PP
+The only other flags that can be specified while changing
+the propagation type are
+.BR MS_REC
+(described below) and
+.BR MS_SILENT
+(which is ignored).
+.PP
+The
+.IR source ,
+.IR filesystemtype ,
+and
+.IR data
+arguments are ignored.
+.PP
+The meanings of the propagation type flags are as follows:
.TP
-.BR MS_SILENT " (since Linux 2.6.17)"
-Suppress the display of certain
-.RI ( printk ())
-warning messages in the kernel log.
-This flag supersedes the misnamed and obsolete
-.BR MS_VERBOSE
-flag (available since Linux 2.4.12), which has the same meaning.
+.BR MS_SHARED
+Make this mount point shared.
+Mount and unmount events immediately under this mount point will propagate
+to the other mount points that are members of this mount's peer group.
+Propagation here means that the same mount or unmount will automatically
+occur under all of the other mount points in the peer group.
+Conversely, mount and unmount events that take place under
+peer mount points will propagate to this mount point.
.TP
-.BR MS_STRICTATIME " (since Linux 2.6.30)"
-Always update the last access time (atime) when files on this
-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
-and
-.BR MS_RELATIME
-flags.
+.BR MS_PRIVATE
+Make this mount point private.
+Mount and unmount events do not propagate into or out of this mount point.
.TP
-.B MS_SYNCHRONOUS
-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 filesystem).
+.BR MS_SLAVE
+If this is a shared mount point that is a member of a peer group
+that contains other members, convert it to a slave mount.
+If this is a shared mount point that is a member of a peer group
+that contains no other members, convert it to a private mount.
+Otherwise, the propagation type of the mount point is left unchanged.
+.IP
+When a mount point is a slave,
+mount and unmount events propagate into this mount point from
+the (master) shared peer group of which it was formerly a member.
+Mount and unmount events under this mount point do not propagate to any peer.
+.IP
+A mount point can be the slave of another peer group
+while at the same time sharing mount and unmount events
+with a peer group of which it is a member.
+.TP
+.BR MS_UNBINDABLE
+Make this mount unbindable.
+This is like a private mount,
+and in addition this mount can't be bind mounted.
+When a recursive bind mount
+.RB ( mount ()
+with the
+.BR MS_BIND
+and
+.BR MS_REC
+flags) is performed on a directory subtree,
+any unbindable mounts within the subtree are automatically pruned
+(i.e., not replicated)
+when replicating that subtree to produce the target subtree.
.PP
-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 onward,
-.B MS_NOATIME
+By default, changing the propagation type affects only the
+.I target
+mount point.
+If the
+.B MS_REC
+flag is also specified in
+.IR mountflags ,
+then the propagation type of all mount points under
+.IR target
+is also changed.
+.PP
+For further details regarding mount propagation types
+(including the default propagation type assigned to new mounts), see
+.BR mount_namespaces (7).
+.\"
+.SS Moving a mount
+If
+.I mountflags
+contains the flag
+.BR MS_MOVE
+(available since Linux 2.4.18),
+then move a subtree:
+.I source
+specifies an existing mount point and
+.I target
+specifies the new location to which that mount point is to be relocated.
+The move is atomic: at no point is the subtree unmounted.
+.PP
+The remaining bits in the
+.IR mountflags
+argument are ignored, as are the
+.IR filesystemtype
and
-.B MS_NODIRATIME
-are also settable on a per-mount-point basis.
-The
-.B MS_RELATIME
-flag is also settable on a per-mount-point basis.
+.IR data
+arguments.
+.\"
+.SS Creating a new mount point
+If none of
+.BR MS_REMOUNT ,
+.BR MS_BIND ,
+.BR MS_MOVE ,
+.BR MS_SHARED ,
+.BR MS_PRIVATE ,
+.BR MS_SLAVE ,
+or
+.BR MS_UNBINDABLE
+is specified in
+.IR mountflags ,
+then
+.BR mount ()
+performs its default action: creating a new mount point.
+.IR source
+specifies the source for the new mount point, and
+.IR target
+specifies the directory at which to create the mount point.
.PP
The
+.I filesystemtype
+and
.I data
-argument is interpreted by the different filesystems.
-Typically it is a string of comma-separated options
-understood by this filesystem.
-See
-.BR mount (8)
-for details of the options available for each filesystem type.
+arguments are employed, and further bits may be specified in
+.IR mountflags
+to modify the behavior of the call.
+.\"
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
A component of a path was not searchable.
(See also
.BR path_resolution (7).)
-Or, mounting a read-only filesystem was attempted without giving the
+.TP
+.B EACCES
+Mounting a read-only filesystem was attempted without giving the
.B MS_RDONLY
flag.
-Or, the block device
+.IP
+The file system may be read-only for various reasons, including:
+it resides on a read-only optical disk;
+it is resides on a device with a physical switch that has been set to
+mark the device read-only;
+the filesystem implementation was compiled with read-only support;
+or errors were detected when initially mounting the filesystem,
+so that it was marked read-only
+and can't be remounted as read-write (until the errors are fixed).
+.IP
+Some filesystems instead return the error
+.BR EROFS
+on an attempt to mount a read-only filesystem.
+.TP
+.B EACCES
+The block device
.I source
is located on a filesystem mounted with the
.B MS_NODEV
.\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
.TP
.B EBUSY
+An attempt was made to stack a new mount directly on
+top of an existing mount point that was created in this
+mount namespace with the same
.I source
-is already mounted.
-Or, it cannot be remounted read-only,
+and
+.IR target .
+.TP
+.B EBUSY
+.I source
+cannot be remounted read-only,
because it still holds files open for writing.
-Or, it cannot be mounted on
-.I target
-because
-.I target
-is still busy (it is the working directory of some thread,
-the mount point of another device, has open files, etc.).
.TP
.B EFAULT
One of the pointer arguments points outside the user address space.
.B EINVAL
.I source
had an invalid superblock.
-Or, a remount
+.TP
+.B EINVAL
+A remount operation
.RB ( MS_REMOUNT )
was attempted, but
.I source
was not already mounted on
.IR target .
-Or, a move
+.TP
+.B EINVAL
+A move operation
+.RB ( MS_MOVE )
+was attempted, but the mount tree under
+.I source
+includes unbindable mounts and
+.I target
+is a mount point that has propagation type
+.BR MS_SHARED .
+.TP
+.B EINVAL
+A move operation
+.RB ( MS_MOVE )
+was attempted, but the parent mount of
+.I source
+mount has propagation type
+.BR MS_SHARED .
+.TP
+.B EINVAL
+A move operation
.RB ( MS_MOVE )
was attempted, but
.I source
was not a mount point, or was \(aq/\(aq.
.TP
+.B EINVAL
+.I mountflags
+includes more than one of
+.BR MS_SHARED ,
+.BR MS_PRIVATE ,
+.BR MS_SLAVE ,
+or
+.BR MS_UNBINDABLE .
+.TP
+.B EINVAL
+.I mountflags
+includes
+.BR MS_SHARED ,
+.BR MS_PRIVATE ,
+.BR MS_SLAVE ,
+or
+.BR MS_UNBINDABLE
+and also includes a flag other than
+.BR MS_REC
+or
+.BR MS_SILENT .
+.TP
+.BR EINVAL
+An attempt was made to bind mount an unbindable mount.
+.TP
+.BR EINVAL
+In an unprivileged mount namespace
+(i.e., a mount namespace owned by a user namespace
+that was created by an unprivileged user),
+a bind mount operation
+.RB ( MS_BIND )
+was attempted without specifying
+.RB ( MS_REC ),
+which would have revealed the filesystem tree underneath one of
+the submounts of the directory being bound.
+.TP
.B ELOOP
Too many links encountered during pathname resolution.
-Or, a move was attempted, while
+.TP
+.B ELOOP
+A move operation was attempted, and
.I target
is a descendant of
.IR source .
.TP
.B EPERM
The caller does not have the required privileges.
+.TP
+.B EROFS
+Mounting a read-only filesystem was attempted without giving the
+.B MS_RDONLY
+flag.
+See
+.BR EACCES ,
+above.
.SH VERSIONS
The definitions of
.BR MS_DIRSYNC ,
.BR MS_MOVE ,
+.BR MS_PRIVATE ,
.BR MS_REC ,
.BR MS_RELATIME ,
+.BR MS_SHARED ,
+.BR MS_SLAVE ,
+.BR MS_STRICTATIME ,
and
-.BR MS_STRICTATIME
+.BR MS_UNBINDABLE
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 a single filesystem can be mounted 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.
+.PP
The
.I mountflags
argument may have the magic number 0xC0ED (\fBMS_MGC_VAL\fP)
.BR MS_MGC_VAL
was required in kernel versions prior to 2.4,
but since Linux 2.4 is no longer required and is ignored if specified.
-
+.PP
The original
.B MS_SYNC
flag was renamed
when a different
.B MS_SYNC
was added to \fI<mman.h>\fP.
-.LP
+.PP
Before Linux 2.4 an attempt to execute a set-user-ID or set-group-ID program
on a filesystem mounted with
.B MS_NOSUID
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.
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.)
-
+.PP
A child process created by
.BR fork (2)
shares its parent's mount namespace;
the mount namespace is preserved across an
.BR execve (2).
-
+.PP
A process can obtain a private mount namespace if:
it was created using the
.BR clone (2)
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.
-
+.PP
The Linux-specific
-.I /proc/PID/mounts
+.I /proc/[pid]/mounts
file exposes the list of mount points in the mount
-namespace of the process with the specified ID; see
+namespace of the process with the specified ID.
+The
+.I /proc/[pid]/mountinfo
+file exposes even more information about mount points,
+including the propagation type and mount ID information that makes it
+possible to discover the parental relationship between mount points.
+See
.BR proc (5)
-for details.
+and
+.BR mount_namespaces (7)
+for details of these files.
.SH SEE ALSO
+.BR mountpoint (1),
+.BR chroot (2),
+.BR ioctl_iflags (2),
+.BR pivot_root (2),
.BR umount (2),
-.BR namespaces (7),
+.BR mount_namespaces (7),
.BR path_resolution (7),
-.BR lsblk (8),
.BR findmnt (8),
+.BR lsblk (8),
.BR mount (8),
.BR umount (8)
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