Utilizing the 'doas' Command in UNIX Systems (with Examples)

The doas command, found primarily in OpenBSD systems, allows a user to execute commands with the privileges of another user, most commonly root. It is a utility similar to sudo but with a simpler configuration and syntax, making it an efficient choice for quickly granting elevated permissions when necessary.

Run a Command as Root

Code:

doas command

Motivation:
In UNIX-like systems, certain commands require elevated permissions to execute. By using doas, a user can temporarily gain root-level access to execute necessary commands without logging in as the root user. This minimizes the risks associated with having direct root access.

Explanation:

• doas: This is the command used to execute another command with escalated privileges.
• command: This represents the executable or program you wish to launch with root privileges.

Example Output:
If executing doas ls /root, you might see a directory listing of /root, assuming you have sufficient permissions and the doas setup permits it.

Run a Command as Another User

Code:

doas -u user command

Motivation:
There are instances where it’s necessary to run a command with the privileges of a different, non-root user. This could be due to accessing specific files or directories only that user can access or executing processes that require a user’s specific environment settings.

Explanation:

• doas -u: The -u flag signifies that the following entry is the username whose privileges you wish to assume.
• user: This is the username whose permissions you’re impersonating.
• command: This is the executable task you wish to initiate with the designated user’s permissions.

Example Output:
If running doas -u alice touch /home/alice/newfile, the command should create newfile within Alice’s home directory, provided the permissions allow it in the doas.conf.

Launch the Default Shell as Root

Code:

doas -s

Motivation:
Sometimes users need a root shell to perform multiple tasks that require root privileges. Rather than prefix every individual command with doas, starting a root-shell session allows prolonged interactions with the system as the root user, streamlining workflows.

Explanation:

• doas: Initiates the utility for privilege elevation.
• -s: This flag initiates a shell, starting a new session with elevated permissions.

Example Output:
Initiating doas -s might place you in a % or # shell prompt, indicating elevated root privileges depending upon your system’s default shell.

Parse a Configuration File and Check Command Execution

Code:

doas -C config_file command

Motivation:
To ensure security policies are correctly set up in a doas configuration, it might be prudent to verify whether a specific command execution is permissible. This preemptive check helps in debugging configurations without actually running the command.

Explanation:

• doas -C: This flag detail specifies that doas should run in configuration-testing mode.
• config_file: The designated path to a doas configuration file.
• command: A test command you want to verify for run permissions based on the configuration file.

Example Output:
Running doas -C /etc/doas.conf command could result in a successful permission check message or an error if the command is not authorized.

Make doas Request a Password Even After It Was Supplied

Code:

doas -L

Motivation:
Security-conscious environments might require password input for every elevation of privilege. Even if a user has successfully provided a password recently, using -L ensures the current session re-validates credentials, enhancing security.

Explanation:

• doas -L: The -L flag tells doas to clear previous authentications, necessitating new password input even if a prior session was authenticated.

Example Output:
Initiating a command with doas -L will prompt for a password entry, ensuring the user is verified each time anew.

Conclusion:

The doas command is an elegant and secure means of granting elevated permissions in Unix-like Operating Systems. Whether you are running commands as root, another user, initiating a root shell session, verifying allowed commands, or enforcing password re-verification, doas offers streamlined solutions with straightforward syntax. Its utilization not only simplifies system administration tasks but also enhances system security when configured properly.