harvey/sys/man/4/fossil

.TH FOSSIL 4
.SH NAME
fossil \- archival file server
.SH SYNOPSIS
.B fossil/fossil
[
.B -Dt
]
[
.B -c
.I cmd
]...
.PP
.B fossil/flchk
[
.B -f
]
[
.B -c
.I ncache
]
[
.B -h
.I host
]
.I file
.PP
.B fossil/flfmt
[
.B -y
]
[
.B -b
.I blocksize
]
[
.B -h
.I host
]
[
.B -l
.I label
]
[
.B -v
.I score
]
.I file
.SH DESCRIPTION
Fossil
will become 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
.BR ehime .
The Plan 9 distribution file server,
.BR sources ,
is also a fossil server.
.PP
Fossil
is structured as a magnetic disk write buffer
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:
.BR active ,
.BR archive ,
and
.BR snapshot .
.B /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:
.BI /snapshot/ yyyy / mmdd / hhmm \fR,
where
.I yyyy
is the full year,
.I mm
is the month number,
.I dd
is the day number,
.I hh
is the hour,
and
.I mm
is the minute.
The snapshots in
.B /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 
.B /archive
and also named from the date (though not the time) of the snapshot:
.BI /archive/ yyyy / mmdds \fR,
where
.IR yyyy ,
.IR mm ,
and
.I dd
are year, month, and day as before,
and
.I s
is a sequence number if more than one
archival snapshot is done in a day.
For the first snapshot,
.I s
is null.
For the subsequent snapshots,
.I s
is
.BR .1 ,
.BR .2 ,
.BR .3 ,
etc.
The root of the main file system that is frozen
for the first archival snapshot of December 15, 2002
will be named
.BR /archive/2002/1215/ .
.PP
The attach name used in
.IR mount (1)
(see also
.IR mount (2)
and
.IR attach (5))
selects a file system to be served
and optionally a subtree,
in the format
.IB fs \fR[\fB/ dir \fR].
An empty attach name selects
.BR main/active .
.PP
Fossil normally requires all users except
.L none
to provide authentication tickets on each
.IR attach (5).
To keep just anyone from connecting,
.L 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
.LR none .
Authentication can be disabled using the
.B -A
flag to
.B open
(see
.IR fossilcons (8)).
.PP
The groups called
.B noworld
and
.B write
are special on the file server.
Any user belonging to
.B 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
.B noworld
users, except when walking into directories.
If the
.B 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
.RI ( sources.cs.bell-labs.com )
readable by the world but writable only to the developers.
.PP
.I Fossil
starts a new instance of the fossil file server.
It is configured mainly through console commands,
documented in
.IR fossilcons (8).
.PP
The options are:
.TP
.B -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.
.TP
.B -t
Start a file server console on
.BR /dev/cons .
If this option is given,
.I fossil
does not fork itself into the background.
.TP
.BI -c " cmd
Execute the console command
.IR cmd .
This option may be repeated to give multiple
commands.
Typically the only commands given on the
command line are
.RB `` . \fIfile \fR,''
which executes a file containing commands,
and
.RB `` "srv -p" \fIcons \fR,''
which starts a file server console on
.BI /srv/ cons \fR.
See
.IR fossilcons (8)
for more information.
.PD
.PP
.I Flchk
checks the fossil file system stored in
.I file
for inconsistencies.
.I Flchk
prints fossil console commands that may be
executed to take care of
bad pointers
.RB ( clrp ),
bad entries
.RB ( clre ),
bad directory entries
.RB ( clri ),
unreachable blocks
.RB ( 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.
.PP
.I Flchk
does
.I not
modify the file system, so it is safe to
run concurrently with
.IR 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.
.PP
The options are:
.TP
.B -f
Fast mode.
By default,
.I 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,
.I flchk
avoids walking in Venti blocks
whenever possible.
.TP
.BI -c " ncache
Keep a cache of
.I ncache
(by default, 1000)
file system blocks in memory during the check.
.TP
.BI -h " host
Use
.I host
as the Venti server.
.PD
.PP
.I Flfmt
prepares
.I file
as a new fossil file system.
The file system is initialized with three empty directories
.BR active ,
.BR archive ,
and
.BR snapshot ,
as described above.
The options are:
.TP
.B -y
Yes mode.
By default,
.I 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
.B -y
flag is given, no such checks are made.
.TP
.BI -b " blocksize
Set the file system block size (by default, 8192).
.TP
.BI -h " host
Use
.I host
as the Venti server.
.TP
.BI -l " label
Set the textual label on the file system to
.IR label .
The label is only a comment.
.TP
.BI -v " score
Initialize the file system using the vac file
system stored on Venti at
.IR score .
The score should have been generated by
.I fossil
rather than by
.IR vac (1),
so that the appropriate snapshot metadata is present.
.PD
.SH EXAMPLES
.PP
Place the root of the archive file system on
.B /n/dump
and show the modified times of the MIPS C compiler
over all dumps in December 2002:
.IP
.EX
9fs dump
ls -l /n/dump/2002/12*/mips/bin/vc
.EE
.PP
To get only one line of output for each version of the compiler:
.IP
.EX
ls -lp /n/dump/2002/12*/mips/bin/vc | uniq
.EE
.ne 14
.PP
Initialize a new file system, start the server with permission
checking turned off, create a users file, and mount the server:
.IP
.EX
fossil/flfmt /dev/sdC0/fossil
cat >flproto <<EOF
fsys main config /dev/sdC0/fossil
fsys main open -AWP
fsys main
create /active/adm adm sys d775
create /active/adm/users adm sys 664
users -w /active/adm/users
srv -p fscons
srv fossil
EOF
fossil/fossil -c '. flproto'
mount /srv/fossil /n/fossil
.EE
.LP
See the discussion of the
.B users
and
.B uname
commands in
.IR fossilcons (8)
for more about the user table.
.ne 3
.PP
Perhaps because the disk has been corrupted or replaced,
format a new file system using the last archive score printed
on the console:
.IP
.EX
fossil/flfmt -v b9b3...5559 /dev/sdC0/fossil
.EE
.LP
Note that while
.B /snapshot
will be lost,
.B /active
and
.B /archive
will be restored to their contents at the time of the
last archival snapshot.
.ne 3
.PP
Blindly accept the changes prescribed by
.I flchk
(not recommended):
.IP
.EX
fossil/flchk /dev/sdC0/fossil | sed -n 's/^# //p' >>/srv/fscons
.EE
.LP
A better strategy is to vet the output,
filter out any suggestions you're not comfortable with,
and then use the
.I sed
command to prepare the script.
.SH SOURCE
.B /sys/src/cmd/fossil
.SH SEE ALSO
.IR yesterday (1),
.IR fs (4),
.IR srv (4),
.IR fossilcons (8),
.IR venti (8)
.SH BUGS
It is likely 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
.B /snapshot
) with little effort.
.LP
The implementation of
.IR flush (5)
has a race that will be fixed shortly.
It is possible (though, in practice, it happens
very rarely) that 
.I fossil
will respond to a message after responding
to a flush of that message.