Setting User-Level Disk Quotas in Linux

This article will guide you through user-level disk quotas in Linux from scratch, explaining each command, its flags, arguments, and other uses.

1. Understanding Disk Quotas

Disk quotas limit the amount of disk space and number of files (inodes) a user or group can use on a filesystem.

• Block quota: limits storage size (e.g., 50 MB).
• Inode quota: limits number of files (e.g., 100 files).

Quotas help prevent denial-of-service attacks where a user creates too many files or fills up disk space.

2. Checking Filesystem Type

df -Th /home

• df → shows disk usage.
• -T → shows filesystem type.
• -h → human-readable sizes.

Other uses: check other mount points, verify free space, or identify filesystem type before performing FS-specific operations.

3. Editing /etc/fstab for Quotas

Example line for ext4 root filesystem:

/dev/disk/by-id/dm-uuid-xyz / ext4 defaults,usrquota,grpquota 0 1

• usrquota → enable per-user quotas.
• grpquota → enable per-group quotas.

Other uses: add mount options like noatime, ro, noexec for performance or security.

4. Remounting Filesystem

sudo mount -o remount /  
mount | grep " / "

• mount -o remount / → applies new options without rebooting.
• mount | grep " / " → checks active mount options.

Other uses:

• mount -o remount,ro / → switch root FS to read-only.
• mount -o remount,noatime / → disable file access time updates.
• mount | grep /home → check mount status of /home.

5. Installing Quota Tools

If quotacheck is missing:

sudo apt install quota      # Ubuntu/Debian
sudo dnf install quota      # RHEL/Fedora

• Provides quotacheck, quotaon, edquota, repquota, and quota.

6. Creating Quota Database Files

sudo quotacheck -cum /   # user quotas
sudo quotacheck -cgum /  # group quotas

• -c → create quota files.
• -u → check user quotas.
• -g → check group quotas.
• -m → ignore read-only remount.
• -v → verbose.

Other uses: recalculate usage after large deletions or FS repairs.

7. Enabling Quotas

sudo quotaon /

• Turns on quota enforcement on the filesystem.
• quotaon -v / → verbose.

Why errors appear: root FS busy, but repquota will still work.

8. Creating a New User for Testing

sudo adduser testuser
id testuser

• Creates /home/testuser, sets password, adds to /etc/passwd.
• id shows UID, GID, and groups.

9. Setting Quotas for the User

Interactive method:

sudo edquota -u testuser

Columns:

• blocks: current KB usage.
• soft/hard blocks: warning and max size.
• inodes: number of files.
• soft/hard inodes: warning and max file count.

Example for testing:

/dev/mapper/ubuntu--vg-ubuntu--lv    16   20   25   4   5   6

• Soft/hard limits are very low for easy testing.

10. Testing Quotas

Inode test:

su - testuser
cd ~
touch file1 file2 file3 file4 file5 file6

• Soft inode limit warning appears at file 5.
• Hard inode limit error at file 6.

Space test:

dd if=/dev/zero of=file1 bs=10K count=1
dd if=/dev/zero of=file2 bs=10K count=1

• Hard block limit triggers Disk quota exceeded when exceeded.
• quota -u testuser shows current usage vs limits.

11. Verifying Quotas

repquota /        # list all quotas and usage
quota -u testuser  # show specific user usage

• Confirms limits are applied and usage is tracked.
• Even if quotaon gave busy errors, this confirms enforcement.

✅ Summary

We have:

1. Checked filesystem type.
2. Edited /etc/fstab and remounted.
3. Installed quota tools.
4. Created quota database files.
5. Enabled quota enforcement.
6. Created a test user and set quotas.
7. Tested both inode and space limits.
8. Verified everything with repquota and quota.

This covers learning quotas hands-on while also teaching each command, its arguments, flags, and other useful use cases.