The following command will fail, because the parent directory of threedirsdeep does not exist. [feedback]
paul@debian8:~$ mkdir mydir2/mysubdir2/threedirsdeep
mkdir: cannot create directory ‘mydir2/mysubdir2/threedirsdeep’: No such fi\
le or directory
The command mkdir -p allows users to create a directory and subdirectory with one command. [feedback]
paul@debian8:~$ mkdir -p mydir2/mysubdir2/threedirsdeep paul@debian8:~$ cd mydir2 paul@debian8:~/mydir2$ ls -l total 4 drwxr-xr-x 3 paul paul 4096 Sep 17 00:11 mysubdir2 paul@debian8:~/mydir2$ cd mysubdir2 paul@debian8:~/mydir2/mysubdir2$ ls -l total 4 drwxr-xr-x 2 paul paul 4096 Sep 17 00:11 threedirsdeep paul@debian8:~/mydir2/mysubdir2$ cd threedirsdeep/ paul@debian8:~/mydir2/mysubdir2/threedirsdeep$ pwd /home/paul/mydir2/mysubdir2/threedirsdeep