To recursively search all files under /path for a given string run:

find / -xdev f -type -print0 | xargs -0 grep -H "string"

The -xdev argument ignores other filesystems mounted under the given path, avoiding /proc and /dev for example. If, for example, your /home folder is on a different partition, it won't be searched. Run the command again on that specific path.

Some other common filesystem search patterns are covered in:

• Find and Delete the Largest Files on a File System
• Find the Largest Open Files and Their Owner(s) on Linux with lsof
• Find Files Which Have Been Recently Modified or Created
• Find all Hidden Files and Directories on Linux and UNIX-Like Systems (BSD, Solaris)