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mount.2: Document flags used to set propagation type
Document MS_SHARED, MS_PRIVATE, MS_SLAVE, and MS_UNBINDABLE. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk
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man2/mount.2
134
man2/mount.2
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@ -387,45 +387,76 @@ However, see the discussion of remounting above,
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for a method of making an existing bind mount read-only.
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.\"
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.SS Changing the propagation type of an existing mount
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[TBC]
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.\"
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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 being 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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If
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.IR mountflags
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includes one of
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.BR MS_SHARED ,
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.BR MS_PRIVATE ,
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.BR MS_SLAVE ,
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or
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.BR MS_UNBINDABLE
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(all available since Linux 2.6.15),
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then the propagation type of an existing mount is changed.
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If more than one of these flags is specified, an error results.
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The only flags that can be used with changing the propagation type are
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.BR MS_REC
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and
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.BR MS_SILENT .
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The
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.IR source ,
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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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The meanings of the propagation type flags are as follows:
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.TP
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.BR MS_SHARED
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Make this mount point shared.
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Mount and unmount events immediately under this mount point will propagate
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to the other mount points that are members of this mount's peer group.
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Propagation here means that the same mount or unmount will automatically
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occur under all of the other mount points in the peer group.
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Conversely, mount and unmount events that take place under
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peer mount points will propagate to this mount point.
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.TP
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.BR MS_PRIVATE
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Make this mount point private.
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Mount and unmount events do not propagate into or out of this mount point.
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This is the default propagation type for newly created mount points.
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.TP
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.BR MS_SLAVE
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If this is a shared mount point that is a member of a peer group
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that contains other members, convert it to a slave mount.
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If this is a shared mount point that is a member of a peer group
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that contains no other members, convert it to a private mount.
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Otherwise, the propagation type of the mount point is left unchanged.
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When a mount point is a slave,
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mount and unmount events propagate into this mount point from
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the (master) shared peer group of which it was formerly a member.
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Mount and unmount events under this mount point do not propagate to any peer.
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A mount point can be the slave of another peer group
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while at the same time sharing mount and unmount events
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with a peer group of which it is a member.
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.TP
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.BR MS_UNBINDABLE
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Make this mount unbindable.
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This is like a private mount,
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and in addition this mount can't be bind mounted.
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When a recursive bind mount
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.RB ( mount (2)
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with the
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.BR MS_BIND
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and
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.BR MS_REC
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flags) is performed on a directory subtree,
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any bind mounts within the subtree are automatically pruned
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(i.e., not replicated)
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when replicating that subtree to produce the target subtree.
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.\"
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.SS Moving a mount
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If
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@ -533,6 +564,31 @@ 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 EINVAL
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.I mountflags
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includes more than one of
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.BR MS_SHARED ,
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.BR MS_PRIVATE ,
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.BR MS_SLAVE ,
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or
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.BR MS_UNBINDABLE .
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.TP
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.B EINVAL
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.I mountflags
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includes
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.BR MS_SHARED ,
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.BR MS_PRIVATE ,
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.BR MS_SLAVE ,
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or
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.BR MS_UNBINDABLE
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and also includes a flag other than
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.BR MS_REC
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or
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.BR MS_SILENT .
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.TP
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.BR EINVAL
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An attempt was made to bind mount an unbindable mount.
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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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