Add a new user

sudo useradd -r foo
sudo passwd foo
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully

Password hash file

Linux user password hash are stored here: /etc/shadow

Rip it!

sudo john /etc/shadow
Created directory: /root/.john
Using default input encoding: UTF-8
Loaded 3 password hashes with 3 different salts (sha512crypt, crypt(3) $6$ [SHA512 256/256 AVX2 4x])
Cost 1 (iteration count) is 5000 for all loaded hashes
Will run 5 OpenMP threads
Proceeding with single, rules:Wordlist
Press 'q' or Ctrl-C to abort, almost any other key for status
vagrant          (vagrant)
Warning: Only 3 candidates buffered for the current salt, minimum 20
needed for performance.
toor             (root)
Warning: Only 14 candidates buffered for the current salt, minimum 20
needed for performance.
Warning: Only 6 candidates buffered for the current salt, minimum 20
needed for performance.
Warning: Only 16 candidates buffered for the current salt, minimum 20
needed for performance.
Warning: Only 17 candidates buffered for the current salt, minimum 20
needed for performance.
Warning: Only 3 candidates buffered for the current salt, minimum 20
needed for performance.
Almost done: Processing the remaining buffered candidate passwords, if any
Warning: Only 15 candidates buffered for the current salt, minimum 20
needed for performance.
Proceeding with wordlist:/usr/share/john/password.lst, rules:Wordlist
foobar           (foo)
3g 0:00:00:01 DONE 2/3 (2019-05-06 10:39) 1.570g/s 1806p/s 1808c/s 1808C/s 1234qwer..ford
Use the "--show" option to display all of the cracked passwords reliably
Session completed

And user password is...

foobar           (foo)