150 lines
3.4 KiB
Text
Executable file
150 lines
3.4 KiB
Text
Executable file
.TH FS 4
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.SH NAME
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fs \- file server, dump
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.SH SYNOPSIS
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.I none
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.SH DESCRIPTION
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The file server was the main file system for Plan 9.
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It was a stand-alone system that ran on
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a separate computer.
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It served the Plan 9 protocol via the IL/IP
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protocols on Ethernets.
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The name of the main file server at Murray Hill was
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.BR emelie .
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.PP
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The file server normally requires all users except
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.L none
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to provide authentication tickets on each
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.IR attach (5).
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This can be disabled using the
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.B noauth
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configuration command (see
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.IR fsconfig (8)).
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.PP
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The group numbered 9999, normally called
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.BR noworld ,
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is special
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on the file server. Any user belonging to that group has
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attenuated access privileges. Specifically, when checking such
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a user's access to files, the file's permission bits are first ANDed
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with 0770 for normal files or 0771 for directories. The effect is
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to deny world access permissions to
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.B noworld
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users, except
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when walking directories.
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.PP
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The user
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.B none
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is always allowed to attach to
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.B emelie
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without authentication but has minimal permissions.
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.PP
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.B Emelie
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maintains three file systems
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on a combination of disks and
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write-once-read-many (WORM) magneto-optical disks.
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.TP
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.B other
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is a simple disk-based file system not backed by
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the worm.
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.TP
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.B main
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is a worm-based file system with a disk-based
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look-aside cache.
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The disk cache holds
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modified worm blocks
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to overcome the write-once property of the worm.
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The cache also holds recently accessed
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non-modified blocks to
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speed up the effective access time of the worm.
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Occasionally
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(usually daily at 5AM) the modified blocks in the
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disk cache are
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.IR dumped .
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At this time,
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traffic to the file system is halted and the
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modified blocks are relabeled to the unwritten
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portion of the worm.
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After the dump,
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the file system traffic is continued and
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the relabeled blocks are copied to the worm by
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a background process.
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.TP
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.B dump
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Each time the main file system is dumped,
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its root is appended to a subdirectory of the dump file system.
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Since the dump file system is not mirrored with a disk
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cache,
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it is read-only.
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The name of the newly added root is created from the date
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of the dump:
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.BI / yyyy / mmdds\f1.
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Here
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.I yyyy
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is the full year,
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.I mm
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is the month number,
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.I dd
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is the day number and
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.I s
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is a sequence number if more than
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one dump is done in a day.
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For the first dump,
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.I s
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is null.
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For the subsequent dumps
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.I s
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is 1, 2, 3, etc.
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.sp
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The root of the main file system
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that is frozen on the first dump
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of March 1, 1992
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will be named
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.B /1992/0301/
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in the dump file system.
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.SH EXAMPLES
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Place the root of the
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.B dump
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file system on
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.B /n/dump
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and show the modified times of the MIPS C compiler
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over all dumps in February, 1992:
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.IP
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.EX
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9fs dump
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ls -l /n/dump/1992/02??/mips/bin/vc
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.EE
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.PP
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To get only one line of output for each version of the compiler:
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.IP
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.EX
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ls -lp /n/dump/1992/02??/mips/bin/vc | uniq
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.EE
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.PP
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Make the
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.B other
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file system available in directory
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.BR /n/emelieother :
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.IP
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.EX
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mount -c /srv/boot /n/emelieother other
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.EE
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.SH SOURCE
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.B /sys/src/fs
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.SH SEE ALSO
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.IR yesterday (1),
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.IR cwfs (4),
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.IR srv (4),
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.IR fs (8)
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.br
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Sean Quinlan,
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``A Cached WORM File System'',
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.I
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Software \- Practice and Experience,
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December, 1991
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.SH BUGS
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For the moment, the file server serves both the old (third edition) and new (fourth
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edition) versions of 9P, deciding which to serve by sniffing the first packet on each
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connection.
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.PP
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Required IL, thus now deprecated.
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