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.TH FS 4

.SH NAME

fs \- file server, dump

.SH SYNOPSIS

.I none

.SH DESCRIPTION

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

.BR emelie .

.PP

The file server normally requires all users except

.L none

to provide authentication tickets on each

.IR attach (5).

This can be disabled using the

.B noauth

configuration command (see

.IR fsconfig (8)).

.PP

The group numbered 9999, normally called

.BR 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

.B noworld

users, except

when walking directories.

.PP

The user

.B none

is always allowed to attach to

.B emelie

without authentication but has minimal permissions.

.PP

.B Emelie

maintains three file systems

on a combination of disks and

write-once-read-many (WORM) magneto-optical disks.

.TP

.B other

is a simple disk-based file system similar to

.IR kfs (4) .

.TP

.B 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

.IR 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.

.TP

.B 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:

.BI / yyyy / mmdds\f1.

Here

.I yyyy

is the full year,

.I mm

is the month number,

.I dd

is the day number and

.I s

is a sequence number if more than

one dump is done in a day.

For the first dump,

.I s

is null.

For the subsequent dumps

.I s

is 1, 2, 3, etc.

.sp

The root of the main file system

that is frozen on the first dump

of March 1, 1992

will be named

.B /1992/0301/

in the dump file system.

.SH EXAMPLES

Place the root of the

.B dump

file system on

.B /n/dump

and show the modified times of the MIPS C compiler

over all dumps in February, 1992:

.IP

.EX

9fs dump

ls -l /n/dump/1992/02??/mips/bin/vc

.EE

.PP

To get only one line of output for each version of the compiler:

.IP

.EX

ls -lp /n/dump/1992/02??/mips/bin/vc | uniq

.EE

.PP

Make the

.B other

file system available in directory

.BR /n/emelieother :

.IP

.EX

mount -c /srv/boot /n/emelieother other

.EE

.SH SOURCE

.B /sys/src/fs

.SH SEE ALSO

.IR yesterday (1),

.IR cwfs (4),

.IR srv (4),

.IR fs (8)

.br

Sean Quinlan,

``A Cached WORM File System'',

.I

Software \- Practice and Experience,

December, 1991

.SH BUGS

For the moment, the file server serves both the old (third edition) and new (fourth

edition) versions of 9P, deciding which to serve by sniffing the first packet on each

connection.

.PP

Required IL, thus now deprecated.