Checking Disk Quotas

Limited disk space can be another source of user support calls. Fedora offers the quotas software package for limiting and displaying the amount of disk space that a user can consume. You can also use the du command to see how much disk space has been used in a particular directory (and related subdirectories). To automate the process of checking for disk space, you can create your own script. The following sections describe these ways of dealing with potential disk space problems.

Using quota to check disk usage

A careless or greedy user can gobble up all the space on your hard disk and, possibly, bring your computer to a halt. By using disk quotas, you can limit the amount of disk resources a user or group can use up.

The quota package contains a set of tools that lets you limit the amount of disk space (based on disk blocks) and files (based on inodes) that a user can consume. Using quotas, you can limit the amount of usage (on a per-user and -group basis) for each file system on your computer. The general steps for setting disk quotas are:

1. Edit the /etc/fstab file

2. Create quota files

3. Create and start a quota startup script

4. Create quota rules

5. Check quotas

You set quotas on disk partitions listed in your /etc/fstab file. For computers that are shared by many users, there might be a separate /home or /var partition where users are expected to put all their data. That kind of partition boundary can prevent an entire disk from being consumed by one user. Quotas on the /home or /var partition can make sure that the space within those partitions are shared fairly among your computer’s users.

The procedure that spans the next few sections assumes that you have a separate /home partition on your computer for which you want to create quotas. You could use any partition, not just the /home partition shown in the procedure. For example, if you have only one partition mounted at the root of the files system (/), you could set quotas for your entire file system by replacing /home with / in the following example.

Editing the /etc/fstab file

You need to add quota support to the file system. To do that, edit the /etc/fstab file and add the usrquota option to field number four of the partition for which you want to set quotas. Here is an example of a line from /etc/fstab:

/dev/hda2    /home    ext3    defaults,usrquota,grpquota    1 2 

Here, the /home file system is used to allow disk quotas for all users’ home directories under the /home directory.

Before the usrquota option can take effect, the file system must be remounted. This happens automatically when you reboot, which you will have to do if you are setting quotas for the root (/) file system. Otherwise, you might be able to use the umount and mount commands to cause the usrquota option to take effect.

Creating quota files

You need to have aquota.user and/or aquota.group files in the root directory of the partition on which you want to establish disk quotas. To add quotas based on individual users, you need an aquota.user file, while aquota.group is needed to set quotas based on groups. One way to create these files is with the quotacheck command. Here’s an example of the quotacheck command to create an initial aquota.user file:

 # quotacheck -c /home 

A /home/aquota.user file is created from the previous command. (To create an initial aquota.group file, type touch /home/aquota.group.) Next, you must create the disk usage table for the partition. Here’s an example of how to do that:

 # quotacheck -vug /home 

The quotacheck command in this example looks at the file system partition mounted on /home and builds a table of disk usage. The -v option produces verbose output from the command, the -u option causes user quotas to be examined, and the -g option causes group quotas to be examined. Permissions on the two files are set so only root can access them (chmod 600 aquota.*).

Creating a quota startup script

If the quota package doesn't include a startup script (and it doesn't with the current Fedora distribution), you can create your own. You want this script to check quotas (quotacheck command), start the quota service (quotaon command) and turn off the service (quotaoff command).

Open a new file called /etc/init.d/quota as root user, using any text editor. Here is an example of the content you can add to that file:

#!/bin/bash      # init file for quota  #  # description: Checks disk quotas  #  # processname: quota  # chkconfig: - 90 90  # source function library  . /etc/rc.d/init.d/functions      case "$1" in    start)     echo -n "Checking quotas: "          daemon /sbin/quotacheck -avug     echo     echo -n "Starting quotas: "          daemon /sbin/quotaon -avug     echo     ;;    stop)     echo -n "Shutting down quotas: "     daemon /sbin/quotaoff -a     echo     ;;    restart)          $0 stop          $0 start          ;;    *)     echo "Usage: quota {start|stop|restart}"     exit 1  esac      exit 0  

The quota script, when started, first runs the quotacheck command to check all file systems for which quota checking is on. Then it turns on quota checking with the quotaon command. The line # chkconfig: – 90 90 defines the names assigned to the startup script (S90quota or K90quota) when it is added to the individual run-level directories. When you run chkconfig --add quota in the next step, those scripts are automatically put in the correct run-level directories.

Turn on the quota startup script

If you created a quota file, as described in the previous step, you need to make it executable and set it to start automatically when you start Fedora. To do those things, type the following as root user:

 # chmod 755 /etc/init.d/quota # chkconfig --add quota 

At this point, links are created so that your quota script starts when Fedora boots.

Creating quota rules

You can use the edquota command to create quota rules for a particular user or group. (Valid users and groups are listed in the /etc/passwd and /etc/group files, respectively). Here is an example of an edquota command to set quotas for a user named jake.

Note 

The edquota command uses the vi text editor to edit your quota files. To use a different editor, change the value of the EDITOR or VISUAL environment variable before running edquota. For example, to use the emacs editor, type the following before running edquota:

 # export EDITOR=emacs  

# edquota -u jake  Disk quotas for user jake (uid 501)    Filesystem            blocks   soft   hard   inodes   soft  hard    /dev/hda2                596      0      0        1      0     0  ~  ~  ~  "/tmp//EdP.aBY1zYC" 3L, 215C  

This example shows that user quotas can be set for the user jake on the /dev/hda2 partition (which is /home in our example). Currently, jake has used 596 blocks (a block equals 1K on this ext3 file system). One file was created by jake (represented by 1 inode). To change the disk usage limits, you can edit the zeros (unlimited use) under the soft and hard heading for blocks and inodes.

Soft limits set limits that you don't want a user or group to exceed. Hard limits set the boundaries that you will not let a user or group exceed. After a set grace period that a soft limit is exceeded (which is seven days, by default), the soft limit becomes a hard limit. (Type edquota -t to check and change the grace periods that you have set.)

Here is an example of how the line in the previous edquota example could be changed:

/dev/hda2        596     512000     716800     1     800   1000 

In this example, the soft limit on the number of blocks that the user jake could consume on the /dev/hda2 device (/home) is 512000 blocks (or 500MB); the hard limit is 716800 blocks (or 700MB). Soft and hard limits on inodes are 800 and 1000, respectively. If either of the soft limits are exceeded by the user jake, he has seven days to get back under the limit, or he will be blocked from using any more disk space or inodes.

Further attempts to write to a partition after the hard limit has been exceeded results in a failure to write to the disk. When this happens, the user who tries to create the file that exceeds his limit will see a message like the following:

ide0(3,2): write failed, user block limit reached.  cp: writing 'abc.doc': Disk quota exceeded 

Instead of assigning quotas to users, you can assign quotas to any group listed in the /etc/group file. Instead of the -u option to edquota, use the -g options followed by a group name.

Updating quota settings

After you have changed quota settings for a user, you should rerun the quotacheck command. You should also run the quotacheck command periodically, to keep the quota records up to date. One way to do that is to run the quotacheck command weekly using a cron entry.

Checking quotas

To report on how much disk space and how many inodes each user on your computer (for which you have set quotas) has consumed, use the repquota command. Here’s an example of the repquota command for reading quota data relating to all partitions that are using quotas:

 # repquota -a *** Report for user quotas on device /dev/hda2  Block grace time: 7days: Inode grace time: 7days                       Block limits                  File limits  User         used    soft     hard  grace     used  soft  hard   grace  root  --  1973984       0       0             2506    0     0  jake  --     1296     700    1700   6days        3    0     0  

In this example, jake has exceeded his soft limit of 700 blocks. He currently has six days left in his grace period to remove enough files so that the soft limit does not become the hard limit.

Using du to check disk use

You can discover the most voracious consumers of disk space using the du command. Invoke du with the -s option and give it a list of directories; it reports the total disk space used by all the files in each directory. Add an -h option to display disk space used in numbers, followed by kilobytes (k), megabytes (M), or gigabytes (G). The -c option adds a total of all requested directories at the end. The following checks disk usage for several home directories:

 # du -hcs /home/tom /home/bill /home/tina /home/sally  

This should result in a list of all of your users’ home directories preceded by the number of kilobytes that each directory structure uses. It looks something like this:

339M    /home/tom  81M     /home/bill  31M     /home/tina  44k     /home/sally  450M    total 

Removing temp files automatically

Some potential disk-consumption problems are set up to take care of themselves. For example, directories for storing temporary files used by applications (such as /tmp and /var/tmp) can consume lots of disk space over time. To deal with the problem, Fedora includes the tmpwatch facility. The tmpwatch command runs from the cron file /etc/cron.daily/tmpwatch to delete unused temporary files. Here's what that file contains:

/usr/sbin/tmpwatch 240 /tmp  /usr/sbin/tmpwatch 720 /var/tmp  for d in /var/{cache/man,catman}/{cat?,X11R6/cat?,local/cat?}; do      if [ -d "$d" ]; then      /usr/sbin/tmpwatch -f 720 $d       fi  done 

Each day, this tmpwatch script runs to delete temporary files that haven't been used for a while. Files from the /tmp and /var/tmp directories are removed after 240 and 720 hours of not being accessed, respectively. Temporary man page files stored in /var/cache subdirectories are also checked and deleted after 720 hours of disuse.