• Understanding Linux users and groups

• Manage user accounts

• Manage group accounts

User Accounts

• Creating user account at the command line

  • useradd

  • userdel

  • passwd

• Modifying user accounts

  • usermod

Take a look at the default configuration that if we don't change something gets applied.

useradd -D

Creating a user

• -c "bablu kumar" => comment

• -s "/bin/ksh" => setting a shell

By default, a user is a member of its own group.

Taking a look at /etc/shadow

• (*) => indicates they can't login because they are service accounts.

• (!!) => indicates that no password is set yet.

Adding files to all the users by default

To make sure, all new members get, for example a company policy, in their home directory. We can add that to the /etc/skel

usermod

Locking user account

usermod -L bk => Locks the bk's account

Looking into the /etc/shadow file indicates the account has been locked.

Unlocking the user account

usermod -U bk

Deleting a user

• If you just want to delete the user; userdel username In this case, the user's home directory remains intact.

• Deleting a user including her/his home directory: userdel -r usernameRemember to take a backup before doing it though.

Manage group accounts

• Creating groups at the command line

  • groupadd

  • groupdel

• Creating groups in the GUI

• Modifying groups

  • groupmod

Adding to group usermod

• -a => append to

• -G => a supplemental group

• -g => switch a primary group

You can also check the group information in /etc/group:

usermod -aG wheel bkumar  # Now bkumar can use sudo do tasks that require priviledges on Red Hat systems
usermod -aG admin bkumar # used in Ubuntu (Debian) systems for the same purposes.

• su - it logs into the root account if you have the root's password

• sudo -i it also does the same but once you are in the wheel group, you need to type in your password rather than the root's password which is a safer way.

• sudo visudo contains the configuration file for the sudo management.

• /etc/sudoers.d/ contains some snap in files that lets you add these configurations as snap-ins.

Delete the group: groupdel groupname