User & Group Management

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Adding Users

Adding Users

To add a user, the useradd command can be used.

useradd username

If you want to create a user with it's own home directory, this can be done using the -m flag:

useradd -m username

The default contents of a users home directory are defined within the /etc/skel directory, please see HERE for more info on this.

Adding a system user

useradd -r username

Once created, you'll want to restrict the account by disabling the ability for login, as mentioned here

Default options

There are lots of different options that can be set when creating users and groups, the default options can be viewed using the below command:

useradd -D

Additional options:

-e -expires

-e 2023/12/31

-c - comment

-c "full name"

-s -shell

-s /bin/sh

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Groups

When creating a user, you can also specify groups to add the user to, this is done using the -G flag:

useradd -G groupname username

Comments

When creating a user, you can also opt to add a comment using the -c flag, for example this could be a name:

useradd -c "comment" username

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Passwords

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Set Password

Once a user has been created, you can add a password using the passwd command:

passwd username

Once run, you'll be prompted to enter a new password

Changing password

Changing a users password can be done using the passwd command when signed in as that user.

You can either SSH to the server directly using the required user, or access as root and use su- username to access the user. Once accessed, the passwd command can be run alone to change the password:

passwd

You can also change a users password using root:

passwd username

Additional Options:

chage 

Checking user password metrics (password expiration, last time password changed)

chage -l username

Forcing password change at logon

chage -d 0 username

Temporary Password

When setting a password, you're able to set a temporary placeholder password that can be used to log in by the user, upon logging in the user will be prompted to change to a password of their choice. This can be achieved by using the -e flag after setting a password

passwd username #set as temp password

passwd -e #sets password as expired

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Deleting Users

Deleting Users

Users can be deleted using the userdel command:

userdel username

The above command only removes the user from the system, without removing their home directory.

Remove user and home directory

userdel -r username

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Modifying Users

Post Creation, users can be modified using the usermod command.

Add User To Group

usermod -a -G groupname username

Lock/Unlock Users

Lock User Login

usermod -L username

Unlock User Login

usermod -U username

Disable login access

usermod -s /sbin/nologin username

or we can use the change shell (chsh) command:

chsh -s /bin/nologin username

Change User Home Directory

usermod -d /pathtonewhome username
chown username:usergroup /pathtonewhome

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Groups

Viewing Groups

groups username

Creating Groups

New groups can be created using the groupadd command:

groupadd groupname

Managing group users

Users can be added/removed from a group with 2 main methods, 

1. They can be added when initially created, as mentioned above
2.  They can be added after creation using the usermod command, as mentioned above
3. They can be added using the gpasswd command.

   Add a user to a group

   gpasswd -a username groupname

   Removing a user from a group

   gpasswd -d username groupname

   Add user to a group as an admin

   gpasswd -A username groupname

Deleting groups

Groups can be removed using the groupdel command, note that this doesn't delete the users that are part of this group.

groupdel groupname

Modifying Groups

There are various group properties that can be modified using the groupmod command.

Change Group Name

groupmod -n newname oldname

Change Group ID

groupmod -g NEWID groupname