.TH FS 4
.SH NAME
fs \- file server, dump
.SH SYNOPSIS
.I none
.SH DESCRIPTION
The file server is the main file system for
Plan 9.
It is a stand-alone system that runs on
a separate computer.
It serves the Plan 9 protocol on a variety
of networks including
Datakit/URP,
Ethernet IL/IP and
Cyclone fiber direct connections.
The name of the main file server at Murray Hill is
.BR bootes .
.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 user
.B none
is always allowed to attach to
.B bootes
without authentication but has minimal permissions.
.PP
.B Bootes
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/bootesother :
.IP
.EX
mount -c /srv/boot /n/bootesother other
.EE
.SH SOURCE
.B /sys/src/fs
.SH SEE ALSO
.IR yesterday (1),
.IR srv (4),
.IR fs (8)
.br
Sean Quinlan,
``A Cached WORM File System'',
.I
Software \- Practice and Experience,
December, 1991
