quota

Display disk usage and limits, by default only the user quotas are printed.

Syntax
      quota [ -guv | q ]
      quota [ -uv | q ] user
      quota [ -gv | q ] group

Options
      -g     Print group quotas for the group of which the user
             is a member.

      -u     Print user quotas (this is the default)

      -v     Verbose, will display quotas on filesystems where no
             storage is allocated.

      -q     Print a more terse message, containing only information 
             on filesystems where usage is over quota.

Specifying both -g and -u displays both the user quotas and the group quotas (for the user).

Only the super-user can use the -u flag and the optional user argument to view the limits of other users. Non- super-users can use the the -g flag and optional group argument to view only the limits of groups of which they are members.

The -q flag takes precedence over the -v flag.

Quota reports the quotas of all the filesystems listed in /etc/fstab. For filesystems that are NFS-mounted a call to the rpc.rquotad on the server machine is performed to get the information. If quota exits with a non-zero status, one or more filesystems are over quota.

Files
quota.user located at the filesystem root with user quotas
quota.group located at the filesystem root with group quotas
/etc/fstab to find filesystem names and locations

"We don't wake up for less than $10,000 a day" ~ Linda Evangelista

Related linux commands:

fstab.
edquota.
quotacheck - Scan a file system for disk usage.
quotaon.
repquota.
ulimit - Limit user resources.
Equivalent Windows command: FSUTIL quota - File and Volume utilities.