Understanding the Difference Between sudo and su in Linux

In Linux and Unix-based systems, administrators and users often need elevated privileges to perform certain tasks. Two common commands for obtaining root or superuser access are sudo and su. Although both serve similar purposes, they function differently and are used in distinct scenarios. In this guide, we’ll explore the key differences between sudo and su, how they work, and when to use each one.

What is sudo?

sudo stands for superuser do. It allows permitted users to execute a command as the superuser or another user, as defined by the system’s configuration file (/etc/sudoers). When using sudo, you don't need to log in as the root user; instead, you can run specific commands with elevated privileges.

By default, sudo requires the user to enter their password, and it grants temporary root permissions for the command that follows. It’s a safer method for granting elevated access because it limits the commands a user can run and logs all usage for auditing purposes.

Example of sudo Usage

To update the package list on a Debian-based system, you can use:

sudo apt update  

In this case, the user will be prompted to enter their password to execute the command as the root user.

What is su?

su stands for substitute user or switch user. It is used to switch from one user to another within the system. When used with no arguments, it switches to the root user by default. Unlike sudo, su requires the root password (or the password of the user you're switching to).

When you run su, you essentially start a new shell session with the user’s privileges you switched to. This means all commands you run after switching will be executed with the root user’s permissions (if that’s the account you’ve switched to).

Example of su Usage

To become the root user and run a command, you would use:

su  

You will be prompted to enter the root password. Once authenticated, you’ll be granted root privileges for all subsequent commands.

Alternatively, you can switch to another user by specifying their username:

su username  

Key Differences Between sudo and su

1. Authentication
   • sudo requires the user’s password, not the root password, and grants temporary elevated privileges.
   • su requires the root password (or the target user’s password) and switches to the root user (or specified user) for the entire session.
2. Scope of Privileges
   • sudo grants permissions only for the specific command you are executing, limiting the exposure of elevated access.
   • su grants full administrative rights for the entire shell session, which can be riskier, especially if you forget to exit the root session.
3. Security
   • sudo is more secure because it logs every command executed with elevated privileges, providing a detailed audit trail.
   • su does not create logs of specific commands executed, making it less secure in terms of accountability.
4. Use Cases
   • sudo is typically used when you need to run occasional commands as a superuser, minimizing the potential for accidental mistakes.
   • su is used when you need to switch to the root user or another user and perform multiple administrative tasks within that session.

When to Use sudo vs su

• Use sudo when you only need elevated privileges for a single command or task. It’s the preferred option for security and granularity of control.
• Use su when you need to switch to the root user or another user’s environment for an extended period, allowing you to run multiple commands in that context.

Conclusion

Both sudo and su are essential tools in a Linux administrator's toolbox. Understanding the difference between them can help you make informed decisions about which tool to use for various tasks. sudo is ideal for running single commands with elevated privileges, while su is suitable for full user context switches, especially when performing a series of administrative actions.

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