FS(4)FS(4)NAMEfs - file server, dump
The file server was the main file system for Plan 9. It was a stand-
alone system that ran on a separate computer. It served the Plan 9
protocol via the IL/IP protocols on Ethernets. The name of the main
file server at Murray Hill was emelie.
The file server normally requires all users except to provide authenti‐
cation tickets on each attach(5). This can be disabled using the
noauth configuration command (see fsconfig(8)).
The group numbered 9999, normally called noworld, is special on the
file server. Any user belonging to that group has attenuated access
privileges. Specifically, when checking such a user's access to files,
the file's permission bits are first ANDed with 0770 for normal files
or 0771 for directories. The effect is to deny world access permis‐
sions to noworld users, except when walking directories.
The user none is always allowed to attach to emelie without authentica‐
tion but has minimal permissions.
Emelie maintains three file systems on a combination of disks and
write-once-read-many (WORM) magneto-optical disks.
other is a simple disk-based file system similar to kfs(4).
main is a worm-based file system with a disk-based look-aside cache.
The disk cache holds modified worm blocks to overcome the write-
once property of the worm. The cache also holds recently
accessed non-modified blocks to speed up the effective access
time of the worm. Occasionally (usually daily at 5AM) the modi‐
fied blocks in the disk cache are dumped. At this time, traffic
to the file system is halted and the modified blocks are rela‐
beled to the unwritten portion of the worm. After the dump, the
file system traffic is continued and the relabeled blocks are
copied to the worm by a background process.
dump Each time the main file system is dumped, its root is appended
to a subdirectory of the dump file system. Since the dump file
system is not mirrored with a disk cache, it is read-only. The
name of the newly added root is created from the date of the
dump: /yyyy/mmdds. Here yyyy is the full year, mm is the month
number, dd is the day number and s is a sequence number if more
than one dump is done in a day. For the first dump, s is null.
For the subsequent dumps s is 1, 2, 3, etc.
The root of the main file system that is frozen on the first
dump of March 1, 1992 will be named /1992/0301/ in the dump file
Place the root of the dump file system on /n/dump and show the modified
times of the MIPS C compiler over all dumps in February, 1992:
ls -l /n/dump/1992/02??/mips/bin/vc
To get only one line of output for each version of the compiler:
ls -lp /n/dump/1992/02??/mips/bin/vc | uniq
Make the other file system available in directory /n/emelieother:
mount -c /srv/boot /n/emelieother other
SEE ALSOyesterday(1), cwfs(4), srv(4), fs(8)
Sean Quinlan, ``A Cached WORM File System'', Software - Practice and
Experience, December, 1991
For the moment, the file server serves both the old (third edition) and
new (fourth edition) versions of 9P, deciding which to serve by sniff‐
ing the first packet on each connection.
Required IL, thus now deprecated.