Which command securely opens the sudoers file in an editor for modification?

The command that securely opens the sudoers file for modification is visudo. It is specifically designed for editing the sudoers file because it includes syntax checking and prevents you from saving a file with errors that could lock you out of sudo access. When you use visudo, it opens the sudoers file in the default text editor set for your system. If there are syntax errors upon saving, visudo will alert you and won't permit changes to take effect until those errors are corrected.

Using visudo provides a level of safety against accidental misconfiguration, which is critical since an incorrect sudoers file can lead to losing administrative privileges, hence making it difficult to manage the system effectively. This command ensures that users edit the file in a secure manner, thus minimizing the risk of errors during the editing process.