u9fs - serve 9P from Unix
u9fs [ directory ]
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 to be invoked on a Unix machine by
inetd with its standard input, output, and error connected to a network connection, typi-
cally TCP on an Ethernet. It runs as user root and multiplexes access to multiple Plan 9
clients over the single wire. It simulates Unix permissions itself by assuming Plan 9
uids match Unix login names.
If a directory is specified u9fs first does a Unix chroot system call to that directory.
Plan 9 calls this service 9fs with TCP service number 564 on the Ethernet. Set up this
way on a machine called, say, kremvax, u9fs may be connected to the name space of a Plan 9
Due to a bug in some versions of the 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 ser-
vice as u9fs or 564 and do the srv and mount by hand:
mount -c /srv/tcp!kremvax!u9fs /n/kremvax
For more information on this procedure, see srv(4) and bind(1).
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 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, copy the source to a directory on that system. Edit the makefile to set
LOG to a proper place for a log file and to set the compile-time configuration correctly.
Then compile with an ANSI C compiler and install in /usr/etc/u9fs. Install this line in
9fs stream tcp nowait root /usr/etc/u9fs u9fs
and this in services:
9fs 564/tcp 9fs # Plan 9 fs
Problems are reported to /tmp/u9fs.log. A compile-time flag enables chatty debugging.
bind(1), srv(4), ip(3), nfsserver(8)
The implementation of devices is unsatisfactory.