U9FS(4) U9FS(4)
NAME
u9fs - serve 9P from Unix
SYNOPSIS
u9fs [ -Dnz ] [ -a authtype ] [ -A autharg ] [ -l logfile ]
[ -m msize ] [ -u onlyuser ] fsroot
DESCRIPTION
U9fs 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 net-
work connection, typically TCP on an Ethernet. It typically
runs as user root and multiplexes access to multiple 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 unacceptable to Plan 9 are translated
into a three-character sequence: `\' followed by two hex-
adecimal 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 option below).
-n Signals that u9fs is not being invoked with a
network connection on standard input and output,
and thus should not try to determine 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 use-
ful mainly when debugging with -D.
-a authtype 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 authentica-
tion 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
U9FS(4) U9FS(4)
(see the -A option), is consulted for the
authentication data and should be suitably pro-
tected. 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
-A autharg Used to specify an argument to the authentica-
tion method. See the authentication descrip-
tions above.
-l logfile Specifies the file which should contain debug-
ging output and other messages. The out-of-
the-box compile-time default is /tmp/u9fs.log.
-m msize Set msize for 9P2000 (see open(5)).
-u user 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; oth-
wise, it will serve the entire Unix file system.
EXAMPLES
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
9fs kremvax
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):
srv tcp!kremvax!9fs
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
U9FS(4) U9FS(4)
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.
SOURCE
/sys/src/cmd/unix/u9fs
DIAGNOSTICS
Problems are reported to the log file specified with the -l
option (default /tmp/u9fs.log). The -D flag enables chatty
debugging.
SEE ALSO
bind(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 provide exactly.