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NAME
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fossil, flchk, flfmt – archival file server
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SYNOPSIS
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fossil/fossil [ −Dt ] [ −c cmd ]... [ −f file ] [ −m free-memory-percent
]
fossil/flchk [ −f ] [ −c ncache ] [ −h host ] file
fossil/flfmt [ −y ] [ −b blocksize ] [ −h host ] [ −l label ]
[ −v score ] file
fossil/conf [ −w ] file [ config ]
fossil/last file
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DESCRIPTION
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Fossil is the main file system for Plan 9. Unlike the Plan 9 file
servers of old, fossil is a collection of user-space programs
that run on a standard Plan 9 kernel. The name of the main fossil
file server at Murray Hill is pie. The Plan 9 distribution file
server, sources, is also a fossil server.
Fossil is structured as a magnetic disk write buffer optionally
backed by a Venti server for archival storage. It serves the Plan
9 protocol via TCP. A fossil file server conventionally presents
three trees in the root directory of each file system: active,
archive, and snapshot. /active is the root of a conventional file
system whose blocks are stored
in a disk file. In a typical configuration, the file server periodically
marks the entire file system copy-on-write, effectively taking
a snapshot of the file system at that moment. This snapshot is
made available in a name created from the date and time of the
snapshot: /snapshot/yyyy/mmdd/hhmm where yyyy is the full year,
mm is the month number,
dd is the day number, hh is the hour, and mm is the minute. The
snapshots in /snapshot are ephemeral: eventually they are deleted
to reclaim the disk space they occupy. Long-lasting snapshots
stored on a Venti server are kept in /archive and also named from
the date (though not the time) of the snapshot: /archive/yyyy/mmdds,
where
yyyy, mm, and dd are year, month, and day as before, and s is
a sequence number if more than one archival snapshot is done in
a day. For the first snapshot, s is null. For the subsequent snapshots,
s is .1, .2, .3, etc. The root of the main file system that is
frozen for the first archival snapshot of December 15, 2002 will
be named
/archive/2002/1215/.
The attach name used in mount (see bind(1), bind(2) and attach(5))
selects a file system to be served and optionally a subtree, in
the format fs[/dir]. An empty attach name selects main/active.
Fossil normally requires all users except none to provide authentication
tickets on each attach(5). To keep just anyone from connecting,
none is only allowed to attach after another user has successfully
attached on the same connection. The other user effectively acts
as a chaperone for none. Authentication can be disabled using
the −A flag to open
or srv (see fossilcons(8)).
The groups called noworld and write are special on the file server.
Any user belonging to noworld 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
and 0771 for directories. The effect is to deny world access permissions
to noworld
users, except when walking into directories. If the write group
exists, then the file system appears read-only to users not in
the group. This is used to make the Plan 9 distribution file server
(sources.cs.bell-labs.com) readable by the world but writable
only to the developers.
Fossil starts a new instance of the fossil file server. It is
configured mainly through console commands, documented in fossilcons(8).
The options are:
−D Toggle the debugging flag, which is initially off. When the
flag is set, information about authentication and all protocol
messages are written to standard error.
−t Start a file server console on /dev/cons. If this option is
given, fossil does not fork itself into the background.
−c cmdExecute the console command cmd. This option may be repeated
to give multiple commands. Typically the only commands given on
the command line are “. file,” which executes a file containing
commands, and “srv −pcons,” which starts a file server console
on /srv/cons. See fossilcons(8) for more information.
−f file Read and execute console commands stored in the Fossil
disk file. Conf (q.v.) reads and writes the command set stored
in the disk.
−m Allocate free-memory-percent percent of the available free RAM
for buffers. This overrides all other memory sizing parameters,
notably the −c option to open. 30% is a reasonable choice.
Flchk checks the fossil file system stored in file for inconsistencies.
Flchk is deprecated in favor of the console check command (see
fossilcons(8)). Flchk prints fossil console commands that may
be executed to take care of bad pointers (clrp), bad entries (clre),
bad directory entries (clri), unreachable blocks (bfree). Console
commands are
interspersed with more detailed commentary on the file system.
The commands are distinguished by being prefixed with sharp signs.
Note that all proposed fixes are rather drastic: offending pieces
of file system are simply chopped off.
Flchk does not modify the file system, so it is safe to run concurrently
with fossil, though in this case the list of unreachable blocks
and any inconsistencies involving the active file system should
be taken with a grain of salt.
The options are:
−f Fast mode. By default, flchk checks the entire file system image
for consistency, which includes all the archives to Venti and
can take a very long time. In fast mode, flchk avoids walking
in Venti blocks whenever possible.
−c ncache
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Keep a cache of ncache (by default, 1000) file system blocks in
memory during the check.
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−h hostUse host as the Venti server.
Flfmt prepares file as a new fossil file system. The file system
is initialized with three empty directories active, archive, and
snapshot, as described above. The options are:
−y Yes mode. By default, flfmt will prompt for confirmation before
formatting a file that already contains a fossil file system,
and before formatting a file that is not served directly by a
kernel device. If the −y flag is given, no such checks are made.
−b blocksizeSet the file system block size (by default, 8192).
−h host Use host as the Venti server.
−l label Set the textual label on the file system to label. The
label is only a comment.
−v score Initialize the file system using the vac file system stored
on Venti at score. The score should have been generated by fossil
rather than by vac(1), so that the appropriate snapshot metadata
is present.
Conf reads or writes the configuration branded on the Fossil disk
file. By default, it reads the configuration from the disk and
prints it to standard output. If the −w flag is given, conf reads
a new configuration from config (or else from standard input)
and writes it to the disk. Inside the configuration file, the
argument * may be used to stand in for the name
of the disk holding the configuration. The Plan 9 kernel boot
process runs “fossil −f disk” to start a Fossil file server. The
disk is just a convenient place to store configuration information.
Last prints the vac score that resulted after the most recent
archival snapshot of the fossil in file.
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EXAMPLES
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Place the root of the archive file system on /n/dump and show
the modified times of the MIPS C compiler over all dumps in December
2002:
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9fs dump
ls −l /n/dump/2002/12*/mips/bin/vc
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To get only one line of output for each version of the compiler:
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ls −lp /n/dump/2002/12*/mips/bin/vc | uniq
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Initialize a new file system, start the server with permission
checking turned off, create a users file, and mount the server:
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fossil/flfmt /dev/sdC0/fossil
fossil/conf −w /dev/sdC0/fossil <<EOF
fsys main config
fsys main open −AWP
fsys main
create /active/adm adm sys d775
create /active/adm/users adm sys 664
users −w
srv −p fscons
srv fossil
EOF
fossil/fossil −f /dev/sdC0/fossil
mount /srv/fossil /n/fossil
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See the discussion of the users and uname commands in fossilcons(8)
for more about the user table.
Perhaps because the disk has been corrupted or replaced, format
a new file system using the last archive score printed on the
console:
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fossil/flfmt −v b9b3...5559 /dev/sdC0/fossil
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Note that while /snapshot will be lost, /active and /archive will
be restored to their contents at the time of the last archival
snapshot.
Blindly accept the changes prescribed by flchk (not recommended):
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fossil/flchk /dev/sdC0/fossil | sed −n 's/^# //p' >>/srv/fscons
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A better strategy is to vet the output, filter out any suggestions
you’re not comfortable with, and then use the sed command to prepare
the script.
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SOURCE
SEE ALSO
BUGS
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It is possible that the disk format (but not the Venti format)
will change in the future, to make the disk a full cache rather
than just a write buffer. Changing to the new format will require
reformatting the disk as in the example above, but note that this
will preserve most of the file system (all but /snapshot) with
little effort.
The −m option currently assumes a block size of 8K bytes, and
a single file system per fossil instance.
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