fossil, flchk, flfmt – archival file server


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


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– 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
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
Keep a cache of ncache (by default, 1000) file system blocks in memory during the check.
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.


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:
9fs dump
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/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
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 the script.




yesterday(1), fs(3), fs(4), srv(4), fossilcons(8), loadfossil(8), venti(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.