FS(4) FS(4)
NAME
fs - file server, dump
SYNOPSIS
none
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 Ether-
nets. The name of the main file server at Murray Hill is
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.
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FS(4) FS(4)
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.
EXAMPLES
Place the root of the dump file system on /n/dump and show
the modified times of the MIPS C compiler over all dumps in
February, 1992:
9fs dump
ls -l /n/dump/1992/02??/mips/bin/vc
To get only one line of output for each version of the com-
piler:
ls -lp /n/dump/1992/02??/mips/bin/vc | uniq
Make the other file system available in directory
/n/emelieother:
mount -c /srv/boot /n/emelieother other
SOURCE
/sys/src/fs
SEE ALSO
yesterday(1), srv(4), fs(8)
Sean Quinlan, ``A Cached WORM File System'', Software -
Practice and Experience, December, 1991
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 connec-
tion.
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