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LOCATEDB(5)							   LOCATEDB(5)

       locatedb - front-compressed file name database

       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

       There can be multiple databases.	  Users	 can  select  which  databases
       locate  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 period‐
       ically, typically nightly; see updatedb(1).

GNU LOCATE02 database format
       This is the default format of  databases	 produced  by  updatedb.   The
       updatedb	 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

       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
       additional 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
       locate 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
       bigrams 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.

       Input to frcode:

       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)

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

       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.


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