.TH MUX 4
.SH NAME
mux \- file system multiplexor for failing over
.SH SYNOPSIS
.B mux
[
.B \-abcd
]
[
.B -m
.I mnt
]
.I attr
.I val
.B ...
.SH DESCRIPTION
.I Mux
serves
a name space coresponding to any resource registered using
.IR registry (4)
that matches attributes and values specified by
.I attr
and
.I val
arguments, including special values described in
.IR query (1).
By default, it speaks Styx in the standard input, for use with
.IR mount (1)
as in the example. Flag
.B -m
can be used to ask
.I mux
to mount itself at
.IR mnt .
Options
.B -abc
determine the mount flag, as in
.IR bind (1).
.PP
.I Mux
assumes that, for each registered resource, an attribute with name
.B path
contains an absolute path for reaching its root directory in the current
name space. It simply picks one of the matching resources and serves
(using Styx) its file tree.
.PP
Upon failures (eg., I/O errors) of the resource,
.I mux
switches over to any other resource also matching the attributes.
.PP
Upon failure, open fids for the failing resource report I/O error to the client
process(es). However, any other fids are switched to use files in the new
resource used. Qids are rewritten by
.I mux
so that
.IR bind (2)
could be used, and caching of multiplexed files still works.
.PP
Flag
.B -d
is used to debug the program, and makes it very verbose.
.SH EXAMPLE
Given this registry,
leave at
.B /n/who
any resource named
.B who
that works. Also, mount at
.B /n/uwho
any such resource, as long as its known location is
the same known for the user, as reported in
.BR /n/who/$user/where .
.EX
% cat /mnt/registry/index
pc!where arch Plan9386 loc none path /term/pc/where name where
pc!who arch Plan9386 loc none path /term/pc/who name who
pc!what arch Plan9386 loc none path /term/pc/what name what
Atlantian.local!who loc home path /term/Atlantian.local/who name who
Atlantian.local!what loc home path /term/Atlantian.local/what name what
% mount -Ac {o/mux name who} /n/who
% o/mux -m /n/uwho name who loc '$user'
.EE
.SH SOURCE
.B /usr/octopus/port/mux
.SH SEE ALSO
.IR netget (1).
and
.IR pcns (1).