Where are quota files typically mounted in a Linux system?

Quota files are typically mounted in a Linux system in a manner that allows the system to track disk usage for users and groups. The correct choice is rooted in understanding how file systems and quota management work in Linux.

In the context of quotas, the /etc/mtab file is a significant component because it keeps a record of all currently mounted filesystems, including their options. When quotas are implemented, they are often specified as options in the filesystem's mount command, allowing the system to retrieve and enforce those quotas when users or groups interact with the filesystem.

The other options listed do not serve the purpose of storing or managing quota information in this context. For instance, /sys/block relates to block devices and their underlying structures, /proc/partitions displays information about partitions but not quota management, and /dev/mapper pertains to device mapping and logical volume management without directly handling quota data.

Therefore, /etc/mtab being the file where mounted filesystems and their associated options are recorded is why it is the correct choice for where quota files are typically referenced in a Linux system.