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 directories.
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.
- 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 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.
- 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 system.