Quota

A quota (disk quota) is a mechanism in the operating system or hosting panel that limits the amount of resources assigned to a single user account. It most often governs two figures: used disk space (in megabytes or gigabytes) and the number of files and directories (inodes). Thanks to quotas, one user cannot fill an entire disk and block the other accounts on a shared server.

How a quota works

On Linux systems, disk quotas operate at the filesystem level and distinguish two thresholds:

• Soft quota — a threshold that can be exceeded temporarily; the system generates a warning and starts a grace period, after which the soft limit behaves like a hard one.
• Hard quota — an absolute boundary; once reached, the system refuses to write new data.

A quota can be applied per user or per group. Administrators manage it with tools such as edquota, setquota and repquota, while usage reports feed into the server logs. A separate type is the inode-count limit — it guards against an account filling the system with millions of tiny files without exceeding the space cap.

Quotas in practice

Quotas are a fundamental resource-management tool in hosting:

1. Shared hosting — panels like DirectAdmin, cPanel and Plesk assign each account a space limit matching the purchased hosting plan.
2. Mailboxes — a separate quota per mail account prevents one user from filling the disk.
3. Multi-tenant servers — on machines with many accounts, quotas guarantee a fair split of space.

Regularly monitoring quota usage and pruning old backups helps avoid a sudden limit exhaustion that would halt new writes and email.