fossil, flchk, flfmt - archival file server
fossil/fossil [ -Dt ] [ -c cmd ]... [ -f file ] [ -m free-memory-per‐
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 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 snap‐
shot: /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 /ar‐
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 to provide authentication
tickets on each attach(5). To keep just anyone from connecting, is
only allowed to attach after another user has successfully attached on
the same connection. The other user effectively acts as a chaperone
for Authentication can be disabled using the -A flag to open or srv
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
Fossil starts a new instance of the fossil file server. It is config‐
ured 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 cmd Execute 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 contain‐
ing commands, and ``srv -pcons,'' which starts a file server
console on /srv/cons. See fossilcons(8) for more information.
Read and execute console commands stored in the Fossil disk
file. Conf (q.v.) reads and writes the command set stored in
-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 fossil‐
cons(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 concur‐
rently 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 walk‐
ing in Venti blocks whenever possible.
Keep a cache of ncache (by default, 1000) file system blocks in
memory during the check.
Use 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
Set the file system block size (by default, 8192).
Use host as the Venti server.
Set the textual label on the file system to label. The label is
only a comment.
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
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 configura‐
tion 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 ker‐
nel 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.
Place the root of the archive file system on /n/dump and show the modi‐
fied times of the MIPS C compiler over all dumps in December 2002:
ls -l /n/dump/2002/12*/mips/bin/vc
To get only one line of output for each version of the compiler:
ls -lp /n/dump/2002/12*/mips/bin/vc | uniq
Initialize a new file system, start the server with permission checking
turned off, create a users file, and mount the server:
fossil/conf -w /dev/sdC0/fossil <<EOF
fsys main config
fsys main open -AWP
create /active/adm adm sys d775
create /active/adm/users adm sys 664
srv -p fscons
fossil/fossil -f /dev/sdC0/fossil
mount /srv/fossil /n/fossil
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:
fossil/flfmt -v b9b3...5559 /dev/sdC0/fossil
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):
fossil/flchk /dev/sdC0/fossil | sed -n 's/^# //p' >>/srv/fscons
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
SEE ALSOyesterday(1), fs(3), fs(4), srv(4), fossilcons(8), loadfossil(8),
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.