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Exportfs is a user level file server that allows Plan 9 compute
servers, rather than file servers, to export portions of a name
space across networks. The service is started either by the cpu(1)
command or by a network listener process. An initial protocol
establishes a root directory for the exported name space. The
connection to exportfs is then mounted, typically on /mnt/term.
Exportfs then acts as a relay file server: operations in the imported
file tree are executed on the remote server and the results returned.
This gives the appearance of exporting a name space from a remote
machine into a local file tree.
The options are:
–A address
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Use the address address for aan(8) connections.
–
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a Authenticate the user with the p9any protocol before running
the regular exportfs session; used when exportfs is invoked to
handle an incoming network connection. Exportfs creates a new
name space for each connection, using /lib/namespace by default
(see namespace(6)).
–B address
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Dial address, authenticate as a p9any client, and then serve that
network connection. Requires setting the root of the name space
with –r or –s. The remote system should run import –B to handle the
call. See import(4) for an example.
–
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d –f dbgfile
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Log all 9P traffic to dbgfile (default /tmp/exportdb).
–
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e 'enc auth'
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Set the encryption and authentication algorithms to use for encrypting
the wire traffic (see ssl(3)). The defaults are rc4_256 and sha1.
–
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m msize
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Set the maximum message size that exportfs should offer to send
(see version(5)); this helps tunneled 9P connections to avoid
unnecessary fragmentation.
–
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N nsfile
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Serve the name space described by nsfile.
–
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n Disallow mounts by user none.
–P patternfile
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Restrict the set of exported files. Patternfile contains one regular
expression per line, to be matched against path names relative
to the current working directory and starting with ./. For a file
to be exported, all lines with a prefix + must match and all those
with prefix – must not match.
–
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R Make the served name space read only.
–r root
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Bypass the initial protocol, serving the name space rooted at
root.
–
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S service
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bypass the initial protocol, serving the result of mounting service.
A separate mount is used for each attach(5) message, to correctly
handle servers in which each mount corresponds to a different
client e.g.,( rio(4)).
–
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s equivalent to –r /; kept for compatibility.
The cpu command uses exportfs to serve device files in the terminal.
The import(4) command calls exportfs on a remote machine, permitting
users to access arbitrary pieces of name space on other systems.
Because the kernel disallows reads and writes on mounted pipes
(as might be found in /srv), exportfs calls itself (with appropriate
–m and –S options) to simulate reads and writes on such files.
Srvfs invokes exportprog (default /bin/exportfs) to create a mountable
file system from a name space and posts it at /srv/name, which
is created with mode perm (default 0600). The name space is the
directory tree rooted at path. The –d, –P, and –R options, if present,
are relayed to exportprog.
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