CentOS disk quotas can be enabled both; alerting the system administrator and denying further disk-storage access to a user before disk capacity is exceeded. When a disk is full, depending on what resides on the disk, an entire system can come to a screeching halt until recovered.
Enabling Quota Management in CentOS Linux is basically a 4 step process −
- Step 1 − Enable quota management for groups and users in /etc/fstab.
- Step 2 − Remount the filesystem.
- Step 3 − Create Quota database and generate disk usage table.
- Step 4 − Assign quota policies.
Enable Quota Management in /etc/fstab
First, we want to back up our /etc/fstab file −
[root@centosLocal centos]# cp -r /etc/fstab ./
We now have a copy of our known working /etc/fstab in the current working directory.
#
# /etc/fstab
# Created by anaconda on Sat Dec 17 02:44:51 2016
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/cl-root / xfs defaults 0 0
UUID = 4b9a40bc-9480-4 /boot xfs defaults 0 0
/dev/mapper/cl-home /home xfs defaults,usrquota,grpquota 0 0
/dev/mapper/cl-swap swap swap defaults 0 0
We made the following changes in the options section of /etc/fstab for the volume or Label to where quotas are to be applied for users and groups.
- usrquota
- grpquota
As you can see, we are using the xfs filesystem. When using xfs there are extra manual steps involved. /home is on the same disk as /. Further investigation shows / is set for no quota, which is a kernel-level mounting option. We must re-configure our kernel boot options.
root@localhost rdc]# mount | grep ' / '
/dev/mapper/cl-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
[root@localhost rdc]#
Reconfiguring Kernel Boot Options for XFS File Systems
This step is only necessary under two conditions −
- When the disk/partition we are enabling quotas on, is using the xfs file system
- When the kernel is passing noquota parameter to /etc/fstab at boot time
Step 1 − Make a backup of /etc/default/grub.
cp /etc/default/grub ~/
Step 2 − Modify /etc/default/grub.
Here is the default file.
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
We want to modify the following line −
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet"
to
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv
=cl/swap rhgb quiet rootflags=usrquota,grpquota"
Note − It is important we copy these changes verbatim. After we reconfigure grub.cfg, our system will fail to boot if any errors were made in the configuration. Please, try this part of the tutorial on a non-production system.
Step 3 − Back up your working grub.cfg
cp /boot/grub2/grub.cfg /boot/grub2/grub.cfg.bak
Make a new grub.cfg
[root@localhost rdc]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-514.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-514.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-dbba7fa47f73457b96628ba8f3959bfd
Found initrd image: /boot/initramfs-0-rescuedbba7fa47f73457b96628ba8f3959bfd.img
done
[root@localhost rdc]#
Reboot
[root@localhost rdc]#reboot
If all modifications were precise, we should not have the availability to add quotas to the xfs file system.
[rdc@localhost ~]$ mount | grep ' / '
/dev/mapper/cl-root on / type xfs (rw,relatime,seclabel,attr2,inode64,usrquota,grpquota)
[rdc@localhost ~]$
We have passed the user quota and grpquota parameters via grub.
Now, again edit /etc/fstab to include / since /homeon the same physical disk.
/dev/mapper/cl-root/xfs
defaults,usrquota,grpquota 0 0
Now let’s enable the quota databases.
[root@localhost rdc]# quotacheck -acfvugM
Make sure Quotas are enabled.
[root@localhost rdc]# quotaon -ap
group quota on / (/dev/mapper/cl-root) is on
user quota on / (/dev/mapper/cl-root) is on
group quota on /home (/dev/mapper/cl-home) is on
user quota on /home (/dev/mapper/cl-home) is on
[root@localhost rdc]#
Remount the File System
If the partition or disk is separate from the actively booted partition, we can remount without rebooting. If the quota was configured on a disk/partition booted in the root directory /, we may need to reboot the operating system. Forcing the remount and applying changes, the need to remount the filesystem may vary.
[rdc@localhost ~]$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/cl-root 22447404 4081860 18365544 19% /
devtmpfs 903448 0 903448 0% /dev
tmpfs 919308 100 919208 1% /dev/shm
tmpfs 919308 9180 910128 1% /run
tmpfs 919308 0 919308 0% /sys/fs/cgroup
/dev/sda2 1268736 176612 1092124 14% /boot
/dev/mapper/cl-var 4872192 158024 4714168 4% /var
/dev/mapper/cl-home 18475008 37284 18437724 1% /home
tmpfs 183864 8 183856 1% /run/user/1000
[rdc@localhost ~]$
As we can see, LVM volumes are in use. So it’s simple to just reboot. This will remount /home and load the /etc/fstab configuration changes into active configuration.
Create Quota Database Files
CentOS is now capable of working with disk quotas on /home. To enable full quota support, we must run the quotacheck command.
quotacheck will create two files −
- aquota.user
- aquota.group
These are used to store quota information for the quota-enabled disks/partitions.
Following are the common quotacheck switches.
| Switch | Action |
| -u | Checks for user quotas |
| -g | Checks for group quotas |
| -c | Quotas should be enabled for each file system with enables quotas |
| -v | Displays verbose output |
Add Quota Limits Per User
For this, we will use the edquota command, followed by the username −
[root@localhost rdc]# edquota centos
Disk quotas for user centos (uid 1000):
Filesystem blocks soft hard inodes soft hard
/dev/mapper/cl-root 12 0 0 13 0 0
/dev/mapper/cl-home 4084 0 0 140 0 0
Let’s look at each column.
- Filesystem − It is the filesystem quotas for the user applied to
- blocks − How many blocks the user is currently using on each filesystem
- soft − Set blocks for a soft limit. Soft limit allows the user to carry quota for a given time period
- hard − Set blocks for a hard limit. Hard limit is total allowable quota
- inodes − How many inodes the user is currently using
- soft − Soft inode limit
- hard − Hard inode limit
To check our current quota as a user −
[centos@localhost ~]$ quota
Disk quotas for user centos (uid 1000):
Filesystem blocks quota limit grace files quota limit grace
/dev/mapper/cl-home 6052604 56123456 61234568 475 0 0 [centos@localhost ~]$
Following is an error given to a user when the hard quota limit has exceeded.
[centos@localhost Downloads]$ cp CentOS-7-x86_64-LiveKDE-1611.iso.part ../Desktop/
cp: cannot create regular file ‘../Desktop/CentOS-7-x86_64-LiveKDE-
1611.iso.part’: Disk quota exceeded
[centos@localhost Downloads]$
As we can see, we are closed within this user’s disk quota. Let’s set a soft limit warning. This way, the user will have advance notice before quota limits expire. From experience, you will get end-user complaints when they come into work and need to spend 45 minutes clearing files to actually get to work.
As Administrator, we can check quota usage with the repquota command.
[root@localhost Downloads]# repquota /home
Block limits File limits
User used soft hard grace used soft hard grace
----------------------------------------------------------------------------------------
root -- 0 0 0 3 0 0
centos -+ 6189824 56123456 61234568 541 520 540 6days
[root@localhost Downloads]#
As we can see, the user centos have exceeded their hard block quota and can no longer use any more disk space on /home.
-+denotes a hard quota has been exceeded on the filesystem.
When planning quotas, it is necessary to do a little math. What an Administrator needs to know is: How many users are on the system? How much free space to allocate amongst users/groups? How many bytes make up a block on the file system?
Define quotas in terms of blocks as related to free disk space. It is recommended to leave a “safe” buffer of free space on the file system that will remain in a worst-case scenario: all quotas are simultaneously exceeded. This is especially on a partition that is used by the system for writing logs.
