User & Groups Security

Published on: 22nd Apr 2014

Updated on: 25th Jun 2024

Overview

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

Which commands to use

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
```
To change the file or directory mode using chmod.
- Grant the write permission to the user,
```
sudo chmod -R u+w my_path
sudo chmod -R +w my_path
```
  Both the commands has the same effect and '-R' means recursive.
- Grant the write permission to the group,
```
sudo chmod -R g+w my_path
```
- Grant the write permission to the others,
```
sudo chmod -R o+w my_path
```
- OR grant write permission by combining user (u) and group (g),
```
sudo chmod -R ug+w my_path
```
- Here's the notes in the manual,
```
Each MODE is of the form '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'.
```
  where
  - 'u' - user.
  - 'g' - group
  - 'o' - other ('the world')
  - 'a' - same as the combination of ugo.
  - 'r' - read permission
  - 'w' - write permission
  - 'x' - execute permission if it a file or allows access if it is a directory. If you remove 'x' from a directory, ls command will return 'Permission denied' error.
  - 'X' - (capital X) is to allows access a directory and it has no effects on any file.
  - 's' - set the execution bits. For example, sudo chmod g+s /home/user1 will set the current ACL to be inherited to the new files.
  - 't' - the sticky bit that restricts the directory content to be managed by the owner or root. For example, a sub directory cretated in /tmp where /tmp may have directory created by many programss.
Reference: https://ss64.com/bash/chmod.html

For file permission, please refer to File & Directory.

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Author

Lau Hon Wan, software developer.

User & Groups Security

Overview

Which commands to use

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