Using Linux find Command

Most Linux distributions provide a file index which you can use to search for files. It is updated by the command 'updatedb', part of the "mlocate" package. 

For a quick way to find files inside a directory or subdirectory, the Linux "find" command from "findutils" can be used:

find directory -name filename

find will then return all the occurrences of the given 'filename'. You can use '/' as the directory path for it to recur into.
You can also search for files from a given user with a parameter:

find directory -user user

Or by files that end with a pattern:

find directory -name test*

You can also use it to help out with changing permissions on a directory and all files within, recursively, separating permissions from directories and files:

find /dir/to/chmod/all/dirs -type d -exec chmod 755 {} \;   # recursively changing dir permissions, ‘;’ is very important
find /dir/to/chmod/all/dirs -type f -exec chmod 644 {} \;

This is especially useful if you have messed up the file permissions by doing something like 'chmod -R 644' on directories and sub-directories within.