When you install Linux Ubuntu, the bash shell is set as the default. But did you know that you can actually use other shells as well?
When creating a new user in Linux, you can specify the default shell that the user will use. The option used for this is the useradd command's -s option. If the user is already created, you can change it using the usermod -s command.
This article summarizes the main shells that can be used with the -s option of useradd, their features, and how to check the list of available shells on your current system.
1. Main Shell Types and Features
| Shell Path | Shell Name | Features |
|---|---|---|
/bin/bash |
Bash | The most widely used standard shell. Offers various features such as command editing, autocomplete functionality, and scripting. |
/bin/sh |
Bourne Shell | Lightweight and provides minimal functionality. Mainly used in scripting and restricted environments. |
/bin/zsh |
Z Shell (Zsh) | An extended version of Bash. Offers excellent autocomplete features and customization options. Recently gaining popularity. |
/bin/ksh |
Korn Shell | A shell widely used in commercial environments. Emphasizes speed and efficiency. |
/usr/bin/fish |
Fish Shell | A shell recommended for beginners due to its intuitive usage and powerful autocomplete features. |
/usr/sbin/nologin or /bin/false |
Non-login Shell | Used for direct login blocking. Frequently used when creating system accounts or service accounts. |
2. Checking Available Shells on the Current System
The list of available shells on the current system is stored in the /etc/shells file. You can check it with the following command:
cat /etc/shells
Example output:
/bin/sh
/bin/bash
/usr/bin/bash
/bin/rbash
/usr/bin/rbash
/usr/bin/sh
/bin/dash
/usr/bin/dash
Only the shells listed in this file can be used with the useradd command's -s option.
3. Accurately Checking the Path of the nologin Shell
To verify the exact location of the login-blocking shell (nologin), use the following command:
which nologin
Example output:
/usr/sbin/nologin
Since it may vary between systems, it's advisable to check.
4. Example Use Cases
Adding a User with the Bash Shell
sudo useradd -m -s /bin/bash username
Adding a User with the Zsh Shell
sudo useradd -m -s /bin/zsh username
Adding a System User that Cannot Log In
sudo useradd -r -s /usr/sbin/nologin username
Example command to change an existing user's shell:
sudo usermod -s /usr/sbin/nologin username
Command to check the changed result:
cat /etc/passwd | grep username
Normal output example:
username:x:1004:1004::/home/django:/usr/sbin/nologin
Now that you have a clear understanding of the -s option of useradd and the available shells, manage your accounts safely with the correct shell settings!
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