The repquota command is used to generate a report of disk usage and limits for user quotas, making it the appropriate choice to check which users have reached their disk space limit. quotacheck scans one or more filesystems for disk usage, it initializes, checks, and repairs quotas. However, it does not provide a readable report for administrators. edquota is used to edit user quotas, not to display them. quotaon and quotaoff are used to enable and disable quota enforcement, respectively, and do not display the quota usage. du displays disk usage statistics but does not show the quota limits or which users have reached their limits.