Change Default User Home Directory While Adding a New User:

You can add user using regular useradd command with  -d option:

#useradd –d /tmp/home/admin admin

#passwd admin

How Do I Change Existing User's Home Directory?

You need to use the usermod command to set the user's new login directory. The syntax is as follows:

#usermod -m -d /path_to_new_home_directory userName

Where,

1.       -d dirnanme : Path to new login (home) directory.

2.       -m : The contents of the current home directory will be moved to the new home directory, which is created if it does not already exist.