Using `sudo` on Ubuntu vs. RHEL-Based Distros

Understanding sudo: How It Works on Ubuntu and RHEL-Based Distros

The sudo command is a critical tool in the arsenal of nearly every Linux user. It stands for "superuser do" and allows a permitted user to execute a command with the security privileges of another user, typically the superuser or root. While sudo indeed functions similarly across many Linux distributions, there are nuances and default settings that can differ significantly, particularly between popular distros like Ubuntu and RHEL (Red Hat Enterprise Linux)-based systems, such as CentOS or Fedora. Here, we dive into how sudo works, focusing on its implementation and use in Ubuntu compared to RHEL-based distributions.

Basic Usage of sudo

Regardless of the distribution, the basic usage of sudo remains largely the same. A user prefixed by sudo, when executing a command, is prompted to enter their password. Upon successful authentication, and if the user has the required permission as specified in the sudoers file, the command gets executed with root privileges.

Example:

sudo apt update

This command will run the apt update command with root privileges, which is necessary for updating software packages in Ubuntu.

Configuration: The sudoers File

Both Ubuntu and RHEL-based distributions manage sudo permissions through the /etc/sudoers file. This file contains the rules that users must follow when using the sudo command. It is advisable not to edit this file directly but instead use the visudo command, which checks for syntax errors before saving any modifications, thereby preventing potential lockouts.

Default sudoers Settings on Ubuntu vs. RHEL

Ubuntu: Ubuntu configured sudo in a notably user-friendly way. By default, every user that is created during the installation process is added to the 'sudo' group, and any user in this group can run any command as the superuser. The corresponding line in /etc/sudoers looks like this:

%sudo   ALL=(ALL:ALL) ALL

RHEL-based Distros: On RHEL and its derivatives, user privilege specifications are a bit more conservative. Red Hat's approach generally involves more granularity with administrative privileges. By default, RHEL doesn’t add the initial user to the 'sudo' group; instead, they add the user to the wheel group if the user is to have sudo access. The entry in /etc/sudoers looks like:

%wheel  ALL=(ALL)       ALL

It is worth noting that not every RHEL-based system automatically creates a user with sudo privileges upon installation. On Fedora, however, users are more commonly added to the wheel group during the initial setup, similar to Ubuntu's practices.

Password Prompts and No-Password sudo

One of the areas where Ubuntu and RHEL-based distros often differ is how they handle sudo password prompts.

Ubuntu typically allows consecutive sudo commands to be run without re-entering the password for a period of time (usually 15 minutes), whereas RHEL-based systems may require the password to be entered again more frequently, depending on the configuration.

Ubuntu and some RHEL-based distros also support running sudo without a password by adding the NOPASSWD tag in the sudoers file:

username ALL=(ALL) NOPASSWD: ALL

This setting should be used judiciously, as it can pose a security risk if not managed properly.

Conclusion

While sudo works fundamentally the same across different distributions, small differences, particularly in how sudo privileges are granted and managed, can significantly affect the user experience and system security. Ubuntu's user-friendly configuration allows easier out-of-the-box sudo access, making it an excellent choice for less experienced users. In contrast, RHEL's conservative approach might appeal more to system administrators who prefer to maintain strict control over system permissions.

Understanding these differences will not only help Linux users to operate various systems effectively but also leverage the specific features and security models of each distribution to their advantage. Whether you’re a seasoned system administrator or a new user, knowing how to configure and use sudo correctly is a crucial skill in managing Linux environments.