glocatedb

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
       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
       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
       correct 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
       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.

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://savannah.gnu.org/bugs/?group=findutils.  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 bug-findutils-request@gnu.org.



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