Which filesystem command is utilized to check and repair filesystems?

The command utilized to check and repair filesystems is "fsck," which stands for "file system check." This command is essential for maintaining filesystem integrity on Unix-like operating systems. When executed, fsck inspects the filesystem for inconsistencies and errors, and it can also automatically repair these issues. This makes it crucial for recovering corrupted filesystems or ensuring that filesystems are in a consistent and usable state before they are mounted for access.

In contrast, the other options serve different purposes. The mount command is used to attach a filesystem to a specified location in the directory hierarchy, enabling it to be accessed by users and applications. The backup command refers more generally to creating copies of files or entire filesystems for disaster recovery or data preservation, but it does not check or repair filesystems. The df command provides information about filesystem disk space usage, showing available and used space but does not perform any checks or repairs on the filesystem itself. Thus, fsck is specifically designed for checking and repairing filesystems, making it the right choice for this function.