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How To Set Filesystem Quotas on Ubuntu 20.04

Published on February 11, 2022
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How To Set Filesystem Quotas on Ubuntu 20.04
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Introduction

Quotas are used to limit the amount of disk space a user or group can use on a filesystem. Without such limits, a user could fill up the machine’s disk and cause problems for other users and services.

In this tutorial you will install command line tools to create and inspect disk quotas, then set a quota for an example user.

Prerequisites

  • This tutorial assumes you are logged into an Ubuntu 20.04 server, with a non-root, sudo-enabled user, as described in Initial Server Setup with Ubuntu 20.04. The techniques in this tutorial should generally work on Linux distributions other than Ubuntu, but may require some adaptation.

Step 1 – Installing the Quota Tools

To set and check quotas, you first need to install the quota command line tools using apt. First update the package list, then install the package:

  1. sudo apt update
  2. sudo apt install quota

You can verify that the tools are installed by running the quota command and asking for its version information:

  1. quota --version
Output
Quota utilities version 4.05. . . .

It’s fine if your output shows a slightly different version number.

Next make sure you have the appropriate kernel modules for monitoring quotas.

Step 2 – Installing the Quota Kernel Module

If you are on a cloud-based virtual server, your default Ubuntu Linux installation may not have the kernel modules needed to support quota management. To check, you will use find to search for the quota_v1 and quota_v2 modules in the /lib/modules/... directory:

  1. find /lib/modules/ -type f -name '*quota_v*.ko*'
Output
/lib/modules/5.4.0-99-generic/kernel/fs/quota/quota_v2.ko /lib/modules/5.4.0-99-generic/kernel/fs/quota/quota_v1.ko

Make note of your kernel version – highlighted in the file paths above – as you will need it in a later step. It will likely be different, but as long as the two modules are listed, you’re all set and can skip the rest of this step.

If you get no output from the above command, install the linux-image-extra-virtual package:

  1. sudo apt install linux-image-extra-virtual

This will provide the kernel modules necessary for implementing quotas. Run the previous find command again to verify that the installation was successful.

Next you will update your filesystem mount options to enable quotas on your root filesystem.

Step 3 – Updating Filesystem Mount Options

To activate quotas on a particular filesystem, you need to mount it with a few quota-related options specified. You can do this by updating the filesystem’s entry in the /etc/fstab configuration file. Open that file nano or your preferred text editor:

  1. sudo nano /etc/fstab

This file’s contents will be similar to the following:

/etc/fstab
LABEL=cloudimg-rootfs   /        ext4   defaults        0 0
LABEL=UEFI      /boot/efi       vfat    defaults        0 0

This fstab file is from a virtual server. A desktop or laptop computer will probably have a slightly different fstab, but in most cases you’ll have a / or root filesystem that represents all of your disk space.

The highlighted line indicates the name of the mounted device, the location where it is mounted, the file system type, and the mount options used. The first zero indicates no backups will be made, and the second zero indicates no error-checking will be done on boot.

Update the line pointing to the root filesystem by replacing the defaults option with the following highlighted options:

/etc/fstab
LABEL=cloudimg-rootfs   /        ext4   usrquota,grpquota        0 0
. . .

This change will allow us to enable both user- (usrquota) and group-based (grpquota) quotas on the filesystem. If you only need one or the other, you may leave out the unused option. If your fstab line already had some options listed instead of defaults, you should add the new options to the end of whatever is already there, being sure to separate all options with a comma and no spaces.

Remount the filesystem to make the new options take effect:

  1. sudo mount -o remount /

Here, the -o flag is used to pass the remount option.

Note: Be certain there are no spaces between the options listed in your /etc/fstab file. If you put a space after the , comma, you will see an error like the following:

Output
mount: /etc/fstab: parse error

If you see this message after running the previous mount command, reopen the fstab file, correct any errors, and repeat the mount command before continuing.

You can verify that the new options were used to mount the filesystem by looking at the /proc/mounts file. Here, use grep to show only the root filesystem entry in that file:

  1. cat /proc/mounts | grep ' / '
Output
/dev/vda1 / ext4 rw,relatime,quota,usrquota,grpquota 0 0

Note the two specified options. Now that you have installed your tools and updated your filesystem options, you can turn on the quota system.

Step 4 – Enabling Quotas

Before finally turning on the quota system, you need to manually run the quotacheck command once:

  1. sudo quotacheck -ugm /

This command creates the files /aquota.user and /aquota.group. These files contain information about the limits and usage of the filesystem, and they need to exist before you turn on quota monitoring. The quotacheck parameters used are:

  • u: specifies that a user-based quota file should be created
  • g: indicates that a group-based quota file should be created
  • m: disables remounting the filesystem as read-only while performing the initial tallying of quotas. Remounting the filesystem as read-only will give more accurate results in case a user is actively saving files during the process, but is not necessary during this initial setup.

If you don’t need to enable user- or group-based quotas, you can leave off the corresponding quotacheck option.

You can verify that the appropriate files were created by listing the root directory:

  1. ls /
Output
aquota.group bin dev home initrd.img.old lib64 media opt root sbin srv tmp var vmlinuz.old aquota.user boot etc initrd.img lib lost+found mnt proc run snap sys usr vmlinuz

If you didn’t include the u or g options in the quotacheck command, the corresponding file will be missing.

Next, you will have to add the quota modules to the Linux kernel. Alternatively, you could reboot your server to accomplish the same task. Otherwise, add them manually, replacing the highlighted kernel version with your version found in Step 2:

  1. sudo modprobe quota_v1 -S 5.4.0-99-generic
  2. sudo modprobe quota_v2 -S 5.4.0-99-generic

Now you’re ready to turn on the quota system:

  1. sudo quotaon -v /
quotaon Output
/dev/vda1 [/]: group quotas turned on /dev/vda1 [/]: user quotas turned on

Your server is now monitoring and enforcing quotas, but we’ve not set any yet! Next you’ll set a disk quota for a single user.

Step 5 – Configuring Quotas for a User

There are a few ways you can set quotas for users or groups. Here, you’ll go over how to set quotas with both the edquota and setquota commands.

Using edquota to Set a User Quota

Use the edquota command to edit quotas. Let’s edit your example sammy user’s quota:

  1. sudo edquota -u sammy

The -u option specifies that this is a user quota you’ll be editing. If you’d like to edit a group’s quota instead, use the -g option in its place.

This will open up a file in your default text editor, similar to how crontab -e opens a temporary file for you to edit. The file will look similar to this:

Disk quotas for user sammy (uid 1000):
  Filesystem                   blocks       soft       hard     inodes     soft     hard
  /dev/vda1                        40          0          0         13        0        0

This lists the username and uid, the filesystems that have quotas enabled on them, and the block- and inode-based usage and limits. Setting an inode-based quota would limit how many files and directories a user can create, regardless of the amount of disk space they use. Most people will want block-based quotas, which specifically limit disk space usage. This is what you will configure.

Note: The concept of a block is poorly specified and can change depending on many factors, including which command line tool is reporting them. In the context of setting quotas on Ubuntu, it’s fairly safe to assume that 1 block equals 1 kilobyte of disk space.

In the above listing, your user sammy is using 40 blocks, or 40KB of space on the /dev/vda1 drive. The soft and hard limits are both disabled with a 0 value.

Each type of quota allows you to set both a soft limit and a hard limit. When a user exceeds the soft limit, they are over quota, but they are not immediately prevented from consuming more space or inodes. Instead, some leeway is given: the user has – by default – seven days to get their disk use back under the soft limit. At the end of the seven day grace period, if the user is still over the soft limit it will be treated as a hard limit. A hard limit is less forgiving: all creation of new blocks or inodes is immediately halted when you hit the specified hard limit. This behaves as if the disk is completely out of space: writes will fail, temporary files will fail to be created, and the user will start to see warnings and errors while performing common tasks.

Let’s update your sammy user to have a block quota with a 100MB soft limit, and a 110MB hard limit:

Disk quotas for user sammy (uid 1000):
  Filesystem                   blocks       soft       hard     inodes     soft     hard
  /dev/vda1                        40       100M       110M         13        0        0

Save and close the file. To check the new quota you can use the quota command:

  1. sudo quota -vs sammy
Output
Disk quotas for user sammy (uid 1000): Filesystem space quota limit grace files quota limit grace /dev/vda1 40K 100M 110M 13 0 0

The command outputs your current quota status, and shows that your quota is 100M while your limit is 110M. This corresponds to the soft and hard limits respectively.

Note: If you want your users to be able to check their own quotas without having sudo access, you’ll need to give them permission to read the quota files you created in Step 4. One way to do this would be to make a users group, make those files readable by the users group, and then make sure all your users are also placed in the group.

To learn more about Linux permissions, including user and group ownership, please read An Introduction to Linux Permissions

Using setquota to Set a User Quota

Unlike edquota, setquota will update your user’s quota information in a single command, without an interactive editing step. You will specify the username and the soft and hard limits for both block- and inode-based quotas, and finally the filesystem to apply the quota to:

  1. sudo setquota -u sammy 200M 220M 0 0 /

The above command will double sammy’s block-based quota limits to 200 megabytes and 220 megabytes. The 0 0 for inode-based soft and hard limits indicates that they remain unset. This is required even if you’re not setting any inode-based quotas.

Once again, use the quota command to check your work:

  1. sudo quota -vs sammy
Output
Disk quotas for user sammy (uid 1000): Filesystem space quota limit grace files quota limit grace /dev/vda1 40K 200M 220M 13 0 0

Now that you have set some quotas, let’s find out how to generate a quota report.

Step 6 – Generating Quota Reports

To generate a report on current quota usage for all users on a particular filesystem, use the repquota command:

  1. sudo repquota -s /
Output
*** Report for user quotas on device /dev/vda1 Block grace time: 7days; Inode grace time: 7days Space limits File limits User used soft hard grace used soft hard grace ---------------------------------------------------------------------- root -- 1696M 0K 0K 75018 0 0 daemon -- 64K 0K 0K 4 0 0 man -- 1048K 0K 0K 81 0 0 nobody -- 7664K 0K 0K 3 0 0 syslog -- 2376K 0K 0K 12 0 0 sammy -- 40K 200M 220M 13 0 0

In this instance you’re generating a report for the / root filesystem. The -s command tells repquota to use human-readable numbers when possible. There are a few system users listed, which probably have no quotas set by default. Your user sammy is listed at the bottom, with the amounts used and soft and hard limits.

Also note the Block grace time: 7days callout, and the grace column. If your user was over the soft limit, the grace column would show how much time they had left to get back under the limit.

Step 7 – Configuring a Grace Period for Overages

You can configure the period of time where a user is allowed to float above the soft limit. Use the setquota command to do so:

  1. sudo setquota -t 864000 864000 /

The above command sets both the block and inode grace times to 864000 seconds, or 10 days. This setting applies to all users, and both values must be provided even if you don’t use both types of quota (block vs. inode).

Note that the values must be specified in seconds.

Run repquota again to check that the changes took effect:

  1. sudo repquota -s /
Output
Block grace time: 10days; Inode grace time: 10days . . .

The changes should be reflected immediately in the repquota output.

Conclusion

In this tutorial you installed the quota command line tools, verified that your Linux kernel can handle monitoring quotas, set up a block-based quota for one user, and generated a report on your filesystem’s quota usage.

The following are some common errors you may see when setting up and manipulating filesystem quotas.

quotaon Output
quotaon: cannot find //aquota.group on /dev/vda1 [/] quotaon: cannot find //aquota.user on /dev/vda1 [/]

This is an error you might see if you tried to turn on quotas (using quotaon) before running the initial quotacheck command. The quotacheck command creates the aquota or quota files needed to turn on the quota system. See Step 4 for more information.

quotaon Output
quotaon: using //aquota.group on /dev/vda1 [/]: No such process quotaon: Quota format not supported in kernel. quotaon: using //aquota.user on /dev/vda1 [/]: No such process quotaon: Quota format not supported in kernel.

This quotaon error is telling us that your kernel does not support quotas, or at least doesn’t support the correct version (there is both a quota_v1 and quota_v2 version). This means the kernel modules you need are not installed or are not being loaded properly. On Ubuntu Server the most likely cause of this is using a pared-down installation image on a cloud-based virtual server.

If this is the case, it can be fixed by installing the linux-image-extra-virtual package with apt. See Step 2 for more details.

If this error persists after installation, review Step 4. Make sure you either properly used the modprobe commands, or have rebooted your server if that is a viable option for you.

quota Output
quota: Cannot open quotafile //aquota.user: Permission denied quota: Cannot open quotafile //aquota.user: Permission denied quota: Cannot open quotafile //quota.user: No such file or directory

This is the error you’ll see if you run quota and your current user does not have permission to read the quota files for your filesystem. You (or your system administrator) will need to adjust the file permissions appropriately, or use sudo when running commands that require access to the quota file.

To learn more about Linux permissions, including user and group ownership, please read An Introduction to Linux Permissions.


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Tony Tran

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Developer and author at DigitalOcean.

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Developer and author at DigitalOcean.

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