Ubuntu - manage User & groups security with low level commands

Published on: 22nd Apr 2014

Updated on: 16th Jul 2025

Overview

Here's the commands that you need to do the basic user and group management.

Managing users and groups

To add user, run the following command and it will create user record and an user directory in /home,
```
sudo useradd ftpuser
```
12.Jan.2023 - alternatively, you may use the high level command call adduser which creates the user home directory, ask for password and the user contact information.
```
sudo adduser ftpuser
```
To set password for the given user (in this case, 'ftpuser'), run the following command and then key in the password,
```
sudo passwd ftpuser
```
To view the user who is connected to server, execute one of the following command,
```
who
w
users
```
To view the user groups of the current session in the OS,
```
groups
```
To view all groups in the server,
```
sudo cat /etc/group
```
To add new group,
```
sudo groupadd public
```
To add user to a group,
```
sudo usermod -G public -a ftpuser
```
To check the 'ftpuser' (user ID) belongs to which group,
```
id ftpuser
```
To check my user ID
```
whoami
```

Switching to another user context

16.Jul.2025: sometimes, you want to execute a bash script with a dedicated user ID for the reason of any new files or directories to be created will be under this user ID without having to execute chown. Another advantage is that you are allowed to set the file modification time because the file owner is same as the user who is running the script.

For example, you need to upgrade an application while we want to allow the 'myftpuser' (or any other user ID) to access the new directory created by the script.

runuser -l myftpuser -c "./tools/util/upgrade-app.sh"

Where upgrade-app.sh is calling rsync to copy new files and set the file modification time.

More about security

17.Jan.2025: about sudoer

The following article explains how to add an user to the sudo group without modifying the /etc/sudoers file,

https://www.digitalocean.com/community/tutorials/how-to-create-a-new-sudo-enabled-user-on-ubuntu

For using sudoers file,

https://www.digitalocean.com/community/questions/a-deep-dive-into-the-sudoers-file

The su (switch user) command,

https://phoenixnap.com/kb/su-command-linux-examples

Ubuntu - manage the files & directories with the appropriate access permission

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Author

Lau Hon Wan, software developer.