u9fs - serve 9P from Unix
u9fs [ -Dnz ] [ -a authtype ] [ -A autharg ] [ -l logfile ] [ -m msize
] [ -u onlyuser ] fsroot
DESCRIPTIONU9fs is not a Plan 9 program. Instead it is a program that serves Unix
files to Plan 9 machines using the 9P protocol (see intro(5)). It is
typically invoked on a Unix machine by inetd with its standard input
and output connected to a network connection, typically TCP on an Eth‐
ernet. It typically runs as user root and multiplexes access to multi‐
ple Plan 9 clients over the single wire. It assumes Plan 9 uids match
Unix login names, and changes to the corresponding Unix effective uid
when processing requests. Characters in file and directory names unac‐
ceptable to Plan 9 are translated into a three-character sequence: fol‐
lowed by two hexadecimal digits. U9fs serves both 9P1 (the 9P protocol
as used by the second and third editions of Plan 9) and 9P2000.
The options are:
-D Write very chatty debugging output to the log file (see -l
-n Signals that u9fs is not being invoked with a network connection
on standard input and output, and thus should not try to deter‐
mine the remote address of the connection. This is useful when
u9fs is not invoked from inetd (see examples below).
-z Truncate the log file on startup. This is useful mainly when
debugging with -D.
Sets the authentication method to be used. Authtype should be
rhosts, none, or p9any. The default is rhosts, which uses the
ruserok library call to authenticate users by entries in
/etc/hosts.equiv or $HOME/.rhosts. This default is discouraged
for all but the most controlled networks. Specifying none turns
off authentication altogether. This is useful when u9fs is not
invoked from inetd (see examples below, or srvssh in srv(4)).
Specifying p9any uses the fourth edition Plan 9 authentication
mechanisms. The file /etc/u9fs.key, or autharg if specified
(see the -A option), is consulted for the authentication data
and should be suitably protected. This file must contain
exactly three lines: secret (plaintext password), u9fs-user
(user id), and plan9-auth.dom (authentication domain).
Finally, factotum must be taught a key of the form:
key proto=p9sk1 dom=plan9-auth.dom user=u9fs-user !password=secret
Used to specify an argument to the authentication method. See
the authentication descriptions above.
Specifies the file which should contain debugging output and
other messages. The out-of-the-box compile-time default is
Set msize for 9P2000 (see open(5)).
Treat all attaches as coming from user. This is useful in some
cases when running without inetd; see the examples.
If fsroot is specified, u9fs will serve only that tree; othwise, it
will serve the entire Unix file system.
Plan 9 calls 9P file service 9fs with TCP port number 564. Set up this
way on a machine called, say, kremvax, u9fs may be connected to the
name space of a Plan 9 process by
For more information on this procedure, see srv(4) and bind(1).
By default, u9fs serves the entire file system of the Unix machine. It
forbids access to devices because the program is single-threaded and
may block unpredictably. Using the attach specifier device connects to
a file system identical to the usual system except it only permits
device access (and may block unpredictably):
mount -c /srv/tcp!kremvax!9fs /n/kremvax device
(The 9fs command does not accept an attach specifier.) Even so, device
access may produce unpredictable results if the block size of the
device is greater than 8192, the maximum data size of a 9P message.
The source to u9fs is in the Plan 9 directory /sys/src/cmd/unix/u9fs.
To install u9fs on a Unix system with an ANSI C compiler, copy the
source to a directory on that system and run make. Then install the
binary in /usr/etc/u9fs. Add this line to inetd.conf:
9fs stream tcp nowait root /usr/etc/u9fs u9fs
and this to services:
9fs 564/tcp 9fs # Plan 9 fs
Due to a bug in their IP software, some systems will not accept the
service name 9fs, thinking it a service number because of the initial
digit. If so, run the service as u9fs or 564.
On systems where listeners cannot be started, execnet(4) is useful for
running u9fs via other network mechanisms; the script srvssh in srv(4)
provides this for the ssh protocol.
Problems are reported to the log file specified with the -l option
(default /tmp/u9fs.log). The -D flag enables chatty debugging.
SEE ALSObind(1), execnet(4), srv(4), ip(3), nfsserver(8)BUGS
The implementation of devices is unsatisfactory.
Semantics like remove-on-close or the atomicity of wstat are hard to