Category: Tech

Introduction

Managing user and groups in Linux is an essential administrative task. We will cover the manual method to create a new user and add that user to a group. Also, remove that user in a multi step process. Finally, we will cover selective tasks concerning Groups.

There is a separate article concerning adding the same user to multiple servers using Ansible. We will not duplicate that information here.

Create a User Account

First, get a list of all users on the host.

sudo cat /etc/passwd

Now, create a new user called mark.

sudo adduser mark

Remove a User Account

If we want to fully remove a user we will need to follow several steps.  Also, the user’s files on other remote systems will need to be manually searched for and removed or have the ownership changed.

You can not remove an account if the user is currently logged in. This is because the user will have existing running processes.

Lock the user’s account, so they can not login.

sudo password -l mark

Backup the user’s account data.

sudo tar -zcvf /nas/backups/accounts/removed/mark_011225.tar.gz /home/mark/

See if the user has any running processes and kill them.

sudo ps -u username

sudo killall -9 -u username

Remove the user’s crontab jobs.

sudo crontab -r -u username

If necessary, cancel any running print jobs. (Linux print remove).

sudo lprm -U username

Assign Mark’s files to another user named Tom.

sudo find / -user mark -exec chown tom:tom {} \;

-exec = execute script.
chown tom:tom = Change ownership to tom.
{} = for each file that is found
\ = Terminate script when done.

Since we will be deleting the home and mail spool directories, and we have already made a backup, we do not need or want to search those directories by changing the file permissions right now. This will prevent us from deleting them and lead to orphan files. So we will modify the above command to exclude those. We only want to change ownership for files outside of those two directories.

sudo find / -user mark ( -path /home -o -path /var/spool/mail/mark ) -prune -o -exec chown tom:tom {} \;

-p = path to exclude
-prune = Do not search specified path.
-o = OR

Finally, remove the user’s account. Some users like to use the deluser command and some like to use the older userdel command. They do essentially the same thing. I am using deluser, as it is a higher level command and also deletes the user’s /home directory and mail spool.

sudo deluser --remove-home mark

–remove-home = removes /home and /var/spool/mail.
–remove-all-files = removes /home,/var/spool/mail, and attempts removal of all other files.

Lastly, check to verify there are no remaining files assigned to the user.

sudo find / -user mark -group mark

Create a Group

Lets create a group called analyst.

sudo addgroup analyst

Add a User to a Group

Let’s add the new user mark to the analyst group. NOTE: You must be a member of a group before you can add others to the same group.

sudo usermod -aG analyst mark

-a = Append
-G = Group

NOTE: For centOS systems, need to run the command ‘$ usermod -aG wheel <user>’

Review Group Memberships

Lets see who is in the group analyst and see what groups the user ‘mark’ is in.

sudo cat /etc/group | grep analyst

sudo groups mark

Remove a User from Group

We can remove the user mark from the analyst group. The command is not as clean as adding a user. It is not obvious that these are group commands. You can use either of the two below commands.

sudo deluser mark analyst 

sudo gpasswd -d mark analyst

-d = delete user from group.

Change a File’s Group Permissions

Next, lets change ownership of a file to the group ‘analyst’. Although there are other methods, I prefer the one shown below, as it is more granular. After you change a file’s group permissions, users will not be able to access the file until they log off and back on again.

chown sudo:analyst /home/mark/sample.txt

References

https://linuxize.com/post/how-to-add-and-delete-users-on-ubuntu-18-04/

https://www.digitalocean.com/community/tutorials/how-to-add-and-delete-users-on-an-ubuntu-14-04-vps

Introduction

The apt (aptitude) command is just a a shortened version of the apt-get command. They are synonymous terms. Use the ‘apt’ command to update and manage your installed software packages. Use with Ubuntu or Debian Linux servers.

Update and upgrade your system

# apt update (date your local repository list)
# apt upgrade (update all installed packages)
# apt autoremove (remove packages that were installed as dependencies)
# apt autoclean (clean the /var/cache/apt/archive folder).

List all installed packages

dpkg --list

apt list --installed

Get a list of all packages that can be upgraded

apt list --upgradable

Remove packages with out uninstalling config files

sudo apt remove {package name}

Remove packages including config Files

sudo apt remove --purge {package name}

Repository location

sudo cat /etc/apt/sources.list

sudo ls /etc/apt/sources.list.d

References

https://askubuntu.com/questions/668582/false-disk-full-error-apt-get-unable-to-install-or-remove