Users and Groups

users, who and w commands can be used to check the users logged into the system.
/etc/passwd file contains user info like username and home directory location.
/etc/shadow contains the username and hash.
/etc/group contains info about groups.
File and directory permissions can be viewed using ls -la.
Execute permission for a directory determines if the user can execute a command inside the directory.
Modifying permissions and ownership:
- chmod g-w hello.txt - removes group-write permission
- chmod a=,u=r hello.txt - changes permission for all users to none, and adds read permission for user (file owner)
- chmod 664 hello.txt - read-write permission for user & group, and only read permissions for everyone else
- sudo chown mike hello.txt - change user ownership of file
- sudo chgrp mike hello.txt - change group ownership of file
sudo -u anotheruser cat restricted.txt allows us to read the file as another user.
su newuser can be used to switch user.
passwd can be used to change the user's password; sudo passwd newuser to change another user's password.

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