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LOCATEDB(5)		      File Formats Manual		   LOCATEDB(5)

NAME
       locatedb	- front-compressed file	name database

DESCRIPTION
       This  manual  page  documents the format	of file	name databases for the
       GNU version of locate.  The file	name databases contain lists of	 files
       that  were  in  particular directory trees when the databases were last
       updated.

       There can be multiple databases.	 Users can select which	databases  lo-
       cate searches using an environment variable or command line option; see
       locate(1).  The system administrator can	choose the file	 name  of  the
       default	database,  the frequency with which the	databases are updated,
       and the directories for which they  contain  entries.   Normally,  file
       name  databases	are  updated  by running the updatedb program periodi-
       cally, typically	nightly; see updatedb(1).

GNU LOCATE02 database format
       This is the default format of databases produced	by updatedb.  The  up-
       datedb  program	runs  frcode  to compress the list of file names using
       front-compression, which	reduces	the database size by a factor of 4  to
       5.   Front-compression  (also  known  as	incremental encoding) works as
       follows.

       The database entries are	a sorted list (case-insensitively, for	users'
       convenience).   Since the list is sorted, each entry is likely to share
       a prefix	(initial string) with the previous entry.  Each	database entry
       begins  with an signed offset-differential count	byte, which is the ad-
       ditional	number of characters of	prefix of the preceding	entry  to  use
       beyond the number that the preceding entry is using of its predecessor.
       (The counts can be negative.)  Following	the count is a null-terminated
       ASCII remainder -- the part of the name that follows the	shared prefix.

       If  the	offset-differential  count  is	larger than can	be stored in a
       signed byte (+/-127), the byte has the value 0x80 (binary 10000000) and
       the  actual  count  follows  in a 2-byte	word, with the high byte first
       (network	byte order).  This count can also be negative  (the  sign  bit
       being in	the first of the two bytes).

       Every  database begins with a dummy entry for a file called `LOCATE02',
       which locate checks for to ensure that the database file	has  the  cor-
       rect format; it ignores the entry in doing the search.

       Databases  can  not be concatenated together, even if the first (dummy)
       entry is	trimmed	from all but the first database.  This is because  the
       offset-differential  count in the first entry of	the second and follow-
       ing databases will be wrong.

       In the future, the data within the locate database may not be sorted in
       any particular order.  To obtain	sorted results,	pipe the output	of lo-
       cate through sort -f.

slocate	database format
       The slocate program uses	a database format similar to,  but  not	 quite
       the  same as, GNU locate.  The first byte of the	database specifies its
       security	level.	If the security	level is 0, slocate will  read,	 match
       and  print  filenames  on  the basis of the information in the database
       only.  However, if the security level byte is 1,	slocate	omits  entries
       from  its  output  if  the invoking user	is unable to access them.  The
       second byte of the database is zero.  The second	byte  is  followed  by
       the  first database entry.  The first entry in the database is not pre-
       ceded by	any differential count or dummy	entry.	Instead	the  differen-
       tial count for the first	item is	assumed	to be zero.

       Starting	with the second	entry (if any) in the database,	data is	inter-
       preted as for the GNU LOCATE02 format.

Old Locate Database format
       There is	also an	old database format, used by Unix locate and find pro-
       grams  and  earlier  releases  of the GNU ones.	updatedb runs programs
       called bigram and code to produce old-format databases.	The old	format
       differs	from  the above	description in the following ways.  Instead of
       each entry starting with	an offset-differential count byte  and	ending
       with a null, byte values	from 0 through 28 indicate offset-differential
       counts from -14 through 14.  The	byte value indicating that a long off-
       set-differential	count follows is 0x1e (30), not	0x80.  The long	counts
       are stored in host byte order, which is not  necessarily	 network  byte
       order, and host integer word size, which	is usually 4 bytes.  They also
       represent a count 14 less than their value.  The	database lines have no
       termination  byte; the start of the next	line is	indicated by its first
       byte having a value <= 30.

       In addition, instead of starting	with a dummy entry, the	 old  database
       format  starts with a 256 byte table containing the 128 most common bi-
       grams in	the file list.	A bigram is a pair of adjacent	bytes.	 Bytes
       in  the	database that have the high bit	set are	indexes	(with the high
       bit cleared) into the bigram table.  The	bigram and offset-differential
       count  coding makes these databases 20-25% smaller than the new format,
       but makes them not 8-bit	clean.	Any byte in a file name	that is	in the
       ranges  used  for  the  special	codes is replaced in the database by a
       question	mark, which not	coincidentally is the shell wildcard to	 match
       a single	character.

EXAMPLE
       Input to	frcode:
       /usr/src
       /usr/src/cmd/aardvark.c
       /usr/src/cmd/armadillo.c
       /usr/tmp/zoo

       Length of the longest prefix of the preceding entry to share:
       0 /usr/src
       8 /cmd/aardvark.c
       14 rmadillo.c
       5 tmp/zoo

       Output  from  frcode, with trailing nulls changed to newlines and count
       bytes made printable:
       0 LOCATE02
       0 /usr/src
       8 /cmd/aardvark.c
       6 rmadillo.c
       -9 tmp/zoo

       (6 = 14 - 8, and	-9 = 5 - 14)

SEE ALSO
       find(1),	locate(1), locatedb(5),	xargs(1), Finding  Files  (on-line  in
       Info, or	printed)

BUGS
       The  best  way  to  report  a  bug  is to use the form at http://savan-
       nah.gnu.org/bugs/?group=findutils.  The reason for  this	 is  that  you
       will then be able to track progress in fixing the problem.   Other com-
       ments about locate(1) and about the findutils package in	general	can be
       sent  to	 the bug-findutils mailing list.  To join the list, send email
       to bug-findutils-request@gnu.org.

								   LOCATEDB(5)

NAME | DESCRIPTION | GNU LOCATE02 database format | slocate database format | Old Locate Database format | EXAMPLE | SEE ALSO | BUGS

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