Implementing Linux Disk Quota on XFS: User, Group, and Project Based Limits

Background : Linux Disk Quota limits filesystem resource usage per user, group, or directory, preventing a single entity from exhausting disk space. The article focuses on applying quota on XFS.

Prerequisites :

Kernel must support quota; XFS has built‑in quota support.

Quota works for ordinary users (root is unrestricted).

Disable SELinux for testing.

Ext filesystems limit only at mount‑point level; XFS can limit per directory.

Quota modes :

usrquota : per‑user limits (root excluded).

grpquota : per‑group limits.

prjquota : per‑directory (project) limits, supported by XFS.

Typical workflow :

Disable SELinux.

Edit /etc/fstab to add quota options (e.g., usrquota,grpquota,prjquota ).

Remount the target filesystem.

Verify quota activation with xfs_quota -x -c "state" .

Set limits using xfs_quota commands.

Validate the limits and monitor usage.

xfs_quota command overview :

Common parameters are shown in the following table (image omitted).

Grace time provides a soft‑limit window; when usage exceeds the soft limit, a timer starts, after which writes are blocked.

Step 1 – User‑based quota :

# vi /etc/fstab
# add: /dev/sdb1 /data xfs defaults,nodiratime,noatime,usrquota 1 2

# umount /data
# mount -a

# mount | grep data
/dev/sdb1 on /data type xfs (rw,noatime,nodiratime,attr2,inode64,logbufs=8,logbsize=32k,usrquota)

# xfs_quota -x -c "state"
User quota state on /data (/dev/sdb1)    Accounting: ON
Enforcement: ON

Set a quota for the MySQL user (soft 10 M, hard 20 M) and a 1‑minute grace time:

# xfs_quota -x -c "limit -u bsoft=10M bhard=20M mysql" /data
# xfs_quota -x -c "timer -u -b 1minutes" /data

Test scenarios demonstrate write failures when exceeding hard or soft limits.

Step 2 – Directory (project) quota :

# vi /etc/fstab
/dev/sdb1 /data xfs defaults,nodiratime,noatime,prjquota 1 2

# umount /data
# mount -a

# xfs_quota -x -c "state"
Project quota state on /data (/dev/sdb1)    Accounting: ON
Enforcement: ON

Create project‑directory mapping:

# echo "1:/data/mysqldata" >> /etc/projects
# echo "mysqldata:1" >> /etc/projid
# xfs_quota -x -c "project -s mysqldata" /data

Assign a hard limit of 10 M (soft 6 M) to the project:

# xfs_quota -x -c "limit -p bsoft=6M bhard=10M mysqldata" /data

Testing shows writes stop at the hard limit.

Common operational commands :

# xfs_quota -x -c "disable -up" /data   # temporarily disable
# xfs_quota -x -c "enable -p" /data    # re‑enable
# xfs_quota -x -c "off -up" /data      # permanently disable (requires remount)

Adjusting grace time:

# xfs_quota -x -c "timer -u -b 14days" /data   # user
# xfs_quota -x -c "timer -g -b 14days" /data   # group
# xfs_quota -x -c "timer -p -b 14days" /data   # project

Rebuilding a quota‑controlled directory removes its quota; re‑initialize the project with xfs_quota -x -c "project -s mysqldata" to restore limits.

Summary : The article provides a practical, step‑by‑step procedure for deploying XFS‑based disk quotas, covering user, group, and project limits, testing, common maintenance commands, and how to adjust limits and grace periods.