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 none to provide
authentication 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 permissions to noworld users, except when walking
The user none is always allowed to attach to emelie without authentication
but has minimal permissions.
Emelie maintains three file systems on a combination of disks
and write–once–read–many (WORM) magneto–optical disks.
mainis 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
is a simple disk–based file system similar to kfs(4).
dumpEach 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
modified blocks in the disk cache are dumped. At this time, traffic
to the file system is halted and the modified blocks are relabeled
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.
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 system.