.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 via the IL/IP
protocols on Ethernets.
The name of the main file server at Coraid is
.BR ila ,
the backup file server is
.BR plano .
.PP
The file server normally requires all users except
.L none
to provide authentication tickets on each
.IR attach (5).
This can be disabled with
.B "flag authdisable"
at the file server console (see
.IR fs (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 ila
without authentication but has minimal permissions.
.PP
.B Ila
maintains three file systems
on Coraid SR1521s.
.TP
.B other
is a simple disk-based file system similar to
.IR kfs (4) .
.TP
.B main
is a WORM file system with a read-write cache.
Only blocks written since the last dump are in the
cache.
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 June 11, 2004
will be named
.B /2004/0611/
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/other :
.IP
.EX
mount -c /srv/boot /n/other 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
.br
Erik Quanstrom
``The Diskless Fileserver'',
Procedings of IWP9,
December, 2007.
.SH BUGS
No MP support.