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locatedb(5)                                                        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
       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
       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
       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 cannot 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.


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

       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)

findutils 4.6.0 - Generated Sun Jan 31 16:56:14 CST 2016
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