Man Linux: Main Page and Category List


       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
       periodically, 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
       correct 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
       following 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
       preceded  by  any  differential  count  or  dummy  entry.   Instead the
       differential count for the first item is assumed to be zero.

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

Old Locate Database format

       There  is  also  an  old  database format, used by Unix locate and find
       programs 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
       offset-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   The reason for this is
       that you will then be able to track progress  in  fixing  the  problem.
       Other  comments  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