The locate command is often the simplest and quickest way to find the locations of files and directories on Linux and other Unix-like operating systems.
The basic syntax for locate is:
locate [options] name(s)
When used without any options, locate displays every absolute pathname for which the user has access permission that contains any of the names of files and/or directories that are provided to it as arguments (i.e., input data).
The absolute pathname, also referred to as the absolute path or the full path, is the hierarchy of directories from the root directory to the designated file or directory. The root directory is the directory at the very top of the filesystem (i.e., hierarchy of files) that contains all other directories and files on the system and which is designated by a forward slash ( / ). It is important that the absolute pathname is returned both because it tells the exact locations on the system and because it makes it possible to indicate the locations of files or directories that have the same name but different absolute paths.
Thus, for example, the following would list the absolute paths of all files named file1 and all directories named dir1 for which the user had access permission:
locate file1 dir1
It would also list any other absolute pathnames that contained these strings (i.e., sequences of characters), for example /home/john/file123 or /usr/local/mydir1/index.html.
The specificity of locate can be increased by using it together with wildcards or other regular expressions. Wildcards are characters that can be used to substitute for any other character or characters. For example, the star character ( * ) is a wildcard that can represent any single character or any string containing any number of characters. Regular expressions are a string that describes or matches a set of strings, according to certain syntax rules. For example, the following command uses the star wildcard to display all files on the system that have the .png filename extension:
The -q option is used to suppress error messages, such as those that might be returned in the event that the user does not have permission to access designated files or directories. Thus, the following would suppress any error messages in the above example:
locate “*.png” -q
It is often the case that a large number of results will be returned for any query. The -n option followed by an integer limits the results to a specific number. For example, the following command would display only 15 results in a search for files that have an .html extension:
locate -n 15 “*.html”
An alternative is to use a pipe (represented by the vertical bar character) to redirect the output of locate from the display screen to a pager such as more or less, which presents only one screenful of output at a time, for example,
locate “*.html” | less
The -i option performs a case-insensitive search. That is, it will return any results that match the arguments regardless of whether individual letters are lower case or upper case. For example, the following would return all files with the extension .html, .HTML, or some combination thereof:
locate -i “*.HtmL”
On some systems, such as Red Hat, the program slocate is installed by default instead of locate, and entering the locate command activates a script (i.e., a short program) that causes slocate to be launched. slocate provides a secure way to index and quickly search for files on a system by storing file permissions and ownership data so that users will not see files for which they do not have access.
The -V option can be used to show which version of locate is used, including whether it is locate or slocate. Another way to determine whether slocate is being used is to see if an absolute pathname such as /usr/bin/slocate is returned when the following command is issued:
locate and slocate actually search a built-in database, named locate.db or slocate.db, respectively, rather than the entire hard disk drive itself, in order to provide a much shorter searching time. This database is automatically updated on a regular basis by cron, a small program that runs in the background, performing various tasks at regularly scheduled intervals. The updating is performed each night if the computer is on continuously.
Because the database is not updated immediately, recently created files and directories might not show up when searching for them with locate or slocate. Fortunately, however, it is a simple matter to update the database manually, although it might take a few minutes. Manual updating can be accomplished by logging in as the root user (i.e., administrative user), such as by using the su (i.e., substitute user) command, and then issuing the following command:
The same thing can be accomplished by the root user by using locate with its -u (i.e., update) option, i.e.,
For the curious, the database is located at /var/lib/slocate/slocate.db on some systems, such as Red Hat. Its exact location on any particular system can be found by the root user (because ordinary users will not have access permission on most systems) with the locate command as follows:
The database is a binary file (i.e., a non-text file). However, for the really curious user who has root permission, the human-readable portion of its contents can be viewed by first using the strings command to extract all the plain text and by then piping the output to less for displaying one screenful at a time as follows:
strings /var/lib/slocate/slocate.db | less
If it is desired to perform a more sophisticated search, including searching by attributes other than name (e.g., by size, creation date or location), the find command should be used.
Courtesy – Linfo