Linux - Disk Quotas: Solving 'Mountpoint not found' and systemd Race Conditions

The Problem: The Zombie Quota

You’ve added usrquota,grpquota to your /etc/fstab. You’ve remounted the filesystem. But when you run quotacheck -avug, you get: quotacheck: Cannot find filesystem to check or filesystem not mounted with quota option. You’ve triple-checked mount | grep quota and it’s definitely there.

The Root Cause: systemd and the Quota Service

On modern Linux distributions (Ubuntu 20.04+, Debian 11+, RHEL 8+), the initialization of quotas is handled by systemd. There is often a race condition where the kernel has enabled the quota flags on the mount, but the quota user-space tools can’t “hook” into the mount because the aquota.user files don’t exist yet, or are being blocked by a stale lock.

The Ideal Fix: The Manual Re-initialisation

When the automated tools fail, you must perform the ritual of manual initialisation.

1. Force the remount

Sometimes a simple mount -o remount isn’t enough to trigger the quota subsystem in the kernel.

sudo mount -o remount,usrquota,grpquota /home

2. Create the Index Files Manually

The quotacheck tool needs the binary index files to exist in the root of the partition.

sudo touch /home/aquota.user /home/aquota.group
sudo chmod 600 /home/aquota.*

3. The ‘Master’ Check Command

Use the -m (don’t remount read-only) and -u/g flags specifically:

sudo quotacheck -cum /home
sudo quotaon -v /home

Tips & Tricks

• XFS is Different: If you are using XFS (default on RHEL/CentOS), do not use quotacheck. XFS manages quotas internally. You must enable them at mount time via the rootflags=uquota kernel parameter (for /) or in fstab, and use the xfs_quota tool for management.
• Grace Periods: A well-versed admin always sets a “Grace Period” (usually 7 days). This allows a user to go over their “Soft Limit” temporarily (e.g., to finish a large download) but hard-stops them at the “Hard Limit.”

  sudo setquota -t 604800 604800 /home
  

• Monitoring: Integrate quota usage into your monitoring (Prometheus/Zabbix). Running out of quota feels like a full disk to the user, but df -h will show plenty of space, leading to hours of wasted troubleshooting.

Summary

Disk quotas are a legacy technology that remains essential in multi-user environments. Their interaction with modern init systems can be flaky, but by understanding how the kernel tracks quota binary files, you can consistently resolve the “Mountpoint not found” error.