When managing disk space on Linux systems, many developers confuse the output of df with their actual disk quota. While df -h shows available space on the filesystem, it doesn't reflect user/group quotas that might be enforced by the system administrator.

For systems with quotas enabled, you'll need specific commands:

# For user quotas:
quota -vs

# For group quotas:
quota -vsg

# Alternative commands that might work:
repquota -a
edquota -u $USER

Here's what you might see from quota -vs:

Disk quotas for user developer (uid 1001):
     Filesystem   space   quota   limit   grace   files   quota   limit   grace
      /dev/sda1    15G     20G     25G              12k      0       0

The key fields show:

• space: Currently used
• quota: Soft limit (you can temporarily exceed)
• limit: Hard maximum
• grace: Time remaining if over soft limit

If the system doesn't have quota tools installed, check for these alternatives:

# Check if quota is enabled on a filesystem:
cat /proc/mounts | grep quota

# Modern systems might use:
systemctl list-units --type=service | grep quota

For regular monitoring, you might want a script like this:

#!/bin/bash
CURRENT=$(quota -vs | awk '/\/dev/ {print $2}')
LIMIT=$(quota -vs | awk '/\/dev/ {print $4}')
PERCENT=$((100*$CURRENT/$LIMIT))

if [ $PERCENT -gt 90 ]; then
    echo "Warning: Disk usage at $PERCENT% of quota"
fi

When working on shared Linux systems or managed servers, you'll often encounter two different disk space measurements:

• df shows physical disk usage across the entire filesystem
• Quota represents your allocated space limit as a user

For systems with quota enforcement, use these commands:

# Basic quota check
quota -v

# More detailed output (requires admin privileges)
repquota -a

On newer Linux distributions with cgroups v2:

# Check your user.slice disk limits
systemd-cgtop
cat /sys/fs/cgroup/user.slice/user-$(id -u).slice/user@$(id -u).service/memory.current

For AWS EC2 instances with EBS volumes:

# Check both physical space and provisioned IOPS
df -h
aws ec2 describe-volumes --volume-ids vol-1234567890abcdef0 --query 'Volumes[0].{Size:Size,IOPS:Iops}'

For Google Cloud persistent disks:

gcloud compute disks describe DISK_NAME --zone ZONE --format="value(sizeGb,physicalBlockSizeBytes)"

Here's a Python script to check and alert when nearing quota limits:

import subprocess
import shlex

def check_quota():
    cmd = "quota -w | grep -A1 'Filesystem' | tail -n1"
    output = subprocess.run(shlex.split(cmd), capture_output=True, text=True)
    parts = output.stdout.split()
    
    used = int(parts[2])
    limit = int(parts[3])
    percent = (used/limit)*100
    
    if percent > 90:
        print(f"WARNING: Quota usage at {percent:.1f}%")
    return percent

if __name__ == "__main__":
    check_quota()

If standard quota commands aren't installed, try these alternatives:

# Check home directory limits (common on HPC systems)
lfs quota -h /home/$USER

# Docker container disk limits
docker system df -v