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Linux User and Group Management

  1. How to add a new group?
  2. How to add a new user?
  3. How to switch from one user to another user?
  4. How to get information about a particular user?
  5. How to delete a user?
  6. How to delete a group?
  7. How to change the ownership of a file?
  8. How to change the group membership of a file?
  9. How to change the group of a user?
  10. How to add a user to multiple groups?
  11. How to check available groups?
  12. How to change the password of a user?
  13. What is the difference between adduser and useradd in Linux?
  14. What is the sudo command?
  15. What is the sudoers file?
  16. How to check the allowed commands by sudo for a particular user?

1. Adding a New Group

To add a group, use the addgroup command with sudo permissions:

sudo addgroup <groupname>

Example:

sudo addgroup pythongroup

Note: All created groups can be viewed in the /etc/group file.

2. Adding a New User

To add a user, use the adduser command. Specify a group using --ingroup if needed:

sudo adduser --ingroup <groupname> <username>

Example:

sudo adduser --ingroup pythongroup pyuser1

If no group is specified, a new group with the same name as the username is created:

sudo adduser pyuser2

Note: User details are stored in the /etc/passwd file:

cat /etc/passwd

3. Switching Between Users

Use the su command to switch users:

su <username>

Example:

su pyuser1

To switch to the root user:

sudo -i

su with and without - Option

  • Without -: Switches user only (keeps the original environment).
  • With -: Switches both user and environment.

4. Viewing User Information

To view a user's information, use the id command:

id <username>

5. Deleting a User

Use the deluser command:

sudo deluser <username>

6. Deleting a Group

Use the delgroup command:

sudo delgroup <groupname>

7. Changing Ownership of a File

Use the chown command:

sudo chown <username>:<groupname> <filename>

8. Changing Group Membership of a File

Use the chgrp command:

sudo chgrp <groupname> <filename>

9. Changing a User's Group

Modify the user's primary group:

sudo usermod -g <groupname> <username>

10. Adding a User to Multiple Groups

Use the usermod command with -aG:

sudo usermod -aG <group1>,<group2> <username>

11. Viewing Available Groups

To list all groups:

cat /etc/group

12. Changing a User's Password

Use the passwd command:

sudo passwd <username>

13. Difference Between adduser and useradd

  • adduser: High-level command, interactive, and user-friendly.
  • useradd: Low-level command, less interactive, requires manual steps.

14. sudo Command

sudo allows a permitted user to execute commands as another user (typically root).

15. sudoers File

The /etc/sudoers file defines permissions for users and groups to execute commands with sudo. Use visudo to safely edit it.

16. Checking Allowed Commands for a User

To see what commands a user can execute with sudo:

sudo -l -U <username>