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.TH BIND 1
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.SH NAME
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bind, mount, unmount \- change name space
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.SH SYNOPSIS
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.B bind
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[
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.I option ...
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]
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.I new old
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.PP
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.B mount
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[
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.I option ...
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]
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.I servename old
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[
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.I spec
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]
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.PP
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.B unmount
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[
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.I new
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]
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.I old
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.SH DESCRIPTION
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.I Bind
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and
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.I mount
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modify the file name space of the current process
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and other processes in the same name space group
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(see
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.IR fork (2)).
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For both calls,
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.I old
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is the name of an existing file or directory in the
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current name space where the modification is to be made.
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.PP
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For
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.IR bind ,
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.I new
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is the name of another (or possibly the same)
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existing file or directory in
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the current name space.
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After a successful
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.IR bind ,
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the file name
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.I old
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is an alias for the object originally named by
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.IR new ;
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if the modification doesn't hide it,
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.I new
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will also still refer to its original file.
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The evaluation of
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.I new
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(see
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.IR intro (2))
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happens at the time of the
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.IR bind ,
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not when the binding is later used.
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.PP
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The
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.I servename
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argument to
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.I mount
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is the name of a file that, when opened, yields an
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existing connection to a file server.
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Almost always,
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.I servename
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will be a file in
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.B /srv
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(see
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.IR srv (3)).
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In the discussion below,
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.I new
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refers to the file named by the
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.I new
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argument to
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.I bind
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or the root directory of the service
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available in
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.I servename
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after a
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.IR mount .
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Either both
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.I old
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and
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.I new
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files must be directories,
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or both must not be directories.
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.PP
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Options control aspects of the modification to the name space:
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.TP 10
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(none)
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Replace the
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.I old
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file by the new one.
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Henceforth, an evaluation of
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.I old
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will be translated to the new file.
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If they are directories (for
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.IR mount ,
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this condition is true by definition),
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.I old
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becomes a
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.I "union directory"
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consisting of one directory (the new file).
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.TP
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.B -b
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Both files must be directories.
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Add the new directory to the beginning
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of the union directory represented by the old file.
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.TP
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.B -a
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Both files must be directories.
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Add the new directory to the end
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of the union directory represented by the old file.
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.TP
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.B -c
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This can be used in addition to any of the above to permit
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creation in a union directory.
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When a new file is created in a union directory,
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it is placed in the first element of the union that has been bound or mounted with the
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.B -c
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flag.
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If that directory does not have write permission, the create fails.
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.TP
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.B -C
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(Only in
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.IR mount .)
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By default, file contents are always retrieved from the server.
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With this option, the kernel may instead use a local cache to satisfy
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.IR read (5)
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requests for files accessible through this mount point.
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The currency of cached data for a file is verified at each
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.IR open (5)
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of the file from this client machine.
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.TP
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.B -q
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Exit silently if the
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.B bind
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or
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.B mount
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operation fails.
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.PD
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.PP
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.I Mount
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takes two additional options.
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The first,
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.B -k
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.IR keypattern ,
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constrains the set of
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.IR factotum (4)
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keys used for an authenticated mount.
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The second,
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.BR -n ,
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causes
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.I mount
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to skip authentication entirely.
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.PP
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The
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.I spec
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argument to
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.I mount
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is passed in the
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.IR attach (5)
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message to the server, and selects among different
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file trees served by the server.
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.PP
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The
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.IR srv (3)
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service registry device, normally bound to
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.BR /srv ,
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is a convenient rendezvous point for services that can be mounted.
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After bootstrap, the file
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.B /srv/boot
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contains the communications port to the file system from which
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the system was loaded.
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.PP
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The effects of
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.I bind
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and
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.I mount
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can be undone with the
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.I unmount
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command.
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If two arguments are given to
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.IR unmount ,
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the effect is to undo a
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.I bind
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or
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.I mount
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with the same arguments.
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If only one argument is given,
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everything bound to or mounted upon
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.I old
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is unmounted.
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.SH EXAMPLES
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To compile a program with the C library from July 16, 1992:
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.IP
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.EX
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mount /srv/boot /n/dump main/archive
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bind /n/dump/1992/0716/mips/lib/libc.a /mips/lib/libc.a
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mk
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.EE
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.SH SOURCE
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.B /sys/src/cmd/bind.c
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.br
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.B /sys/src/cmd/mount.c
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.br
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.B /sys/src/cmd/unmount.c
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.SH SEE ALSO
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.IR bind (2),
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.IR open (2),
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.IR srv (3),
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.IR srv (4)