add a new user  and then add to multiple groups
`adduser user_name`
`usermod -a -G adm,sudo user_name`
`chfn` -> changes full name

change a ownership
`chown file_or_dir user_name`
`chgrp file_or_dir user_name`


delete user
`userdel user_name`
`adduser` -> high-level
`useradd` -> low-level

adduser fc_api 
usermod -a -G sudo fc_api

chown user_name directory/
chgrp user_name directory/

attempted to change password with "Read only file system" as an error, as well a pull a git repository with the same error.
used fsck /dev/sda5 to fix a whole list of issues, problem resolved