If you have install new applications in Unix or Linux operating system, the rehash command can be used to recomputes the internal hash table of the contents of directories listed in the path environmental variable to account for new commands added.

To use rehash command, simply called rehash at command line:

# rehash

rehash will update and refresh the OS’s path environmental variables to include the newly added and installed directories, thus enables users to call the functions and commands from any directory immediately without restarting the server.