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.

Users manipulation

• Adding a new user

adduser <user name>

• Adding a User to the sudoers File

adduser <user name> sudo

• Switching Users

su <user name>

ACCESS

su -    --------------Create New Login Session for User ROOT
su -c 'ls Desktop' ---Execute only one commands donot create login session