21 Making Your Inner

System Administrator

Technique Happy (And

Productive)

Save Time By

Using disk quotas to keep resources in check

Using system accounting to monitor user activity

Watching program activity with system accounting

As system administrator, you want to be sure that system resources are available when needed. Doling out resources to users that need them and keeping track of the overall system performance are

important. Fortunately, tools exist that make it really quick and easy.

Imposing disk quotas is a quick and easy way to control precious system resources. Define user quotas to limit the amount of disk space each user can consume so you’re sure that those who need it can get it.

Disk quotas are self-governing. After you’ve set up the quota (and a grace period), Linux ensures that users can’t use up all your disk space. If you need to know whether you’ve budgeted too little space for some users, a quick glance at the disk quota report tells you how well users are staying within their quotas.

The Linux system accounting package is a small collection of tools that give you quick access to information about how your system is being used. You can quickly determine which users are spending the most time logged in and what resources they’re using. You can also spot programs that shouldn’t be used at all.

In this technique, we show you how to control your system usage. You’re not being a control freak — you’re just ensuring that your users have what they need to get their jobs done.

Reining In Resources with Disk Quotas

If you’re the administrator of a multiuser system, you’ve probably encountered disk hogs — users who download every game or graphic they can find, keep a copy of every e-mail they’ve ever received, and keep multiple copies of work in progress. Such users can cause major disk clogs — especially if your resources are limited.

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Use the diskquota tool to stop resource problems before they start. Placing limits on the storage space or the number of files a user can have on a system will make your users more conscientious about not keeping unneeded files around.

Don’t forget the hyphen when you type in the su - command. The hyphen sets up your search path ($PATH) so you can find the superuser’s tools.

If users exceed their allotted disk space, they receive a warning, and Linux starts a graceperiod countdown. At the end of the grace period, these users are not allowed any additional disk space until they clean up their act.

2. Open the /etc/fstab file in your favorite editor

(which in our case is kedit):

# kedit /etc/fstab

kedit opens, as shown in Figure 21-1.

Installing the quota RPM package

Before you can create and allocate disk quotas, you must install the quota RPM package included with most Linux distributions. To install quota on your system, follow these steps:

1. Open a terminal window and give yourself superuser privileges with the su command.

2. Mount your distribution disc in the CD drive.

3. Use the cd command to move to the directory containing the quota RPM package.

4. Install the quota package with the following command:

# rpm -Uhv quota-version.rpm

That’s all there is to it. The quota package is installed and ready to use.

If you don’t have the distribution disc, but need the package, just Google for it. Downloads of the quota RPM package abound on the Web.

Enabling file system quotas

You can create disk quotas for any file system on your computer, but you have to change the mount options first. To enable quotas for a particular file system, follow these steps:

1. Open a terminal window and give yourself

•Figure 21-1: The /etc/fstab file opened with kedit.

3.Find the file system that you want to modify.

4.Add the usrquota and grpquota options to the fourth column.

Finding the correct column in a typical fstab file can be tricky. The first column contains the device name, the second column specifies the mount point, the third column determines the file system type, and the fourth column contains a commaseparated list of options (typically, defaults):

LABEL=/ / ext3 defaults,usrquota,grpquota 1 1

The preceding code shows the changes needed to add quotas for the root file system.

5.Save your changes and close the editor.

superuser privileges with the su - command.

132 Technique 21: Making Your Inner System Administrator Happy (And Productive)

Now, remount the file system that you modified to enable the new options. The easiest way to remount an active file system is to reboot.

What’s the quickest way to reboot fast? Just type reboot at the command line and press Enter.

Getting your files together

Now it’s time to create the quota control files: aquota.user and aquota.group. These files record the quotas that you assign to each user (or group) on that file system as well as the amount of space currently in use. You’ll find the quota control files in the root directory of each quota-enabled file system. When you create the control files, Linux computes the current disk usage to create a starting point for you.

To create the quota control files, follow these steps:

1. Open a terminal window and give yourself superuser privileges with the su - command.

2. Type the following command and press Enter:

# quotacheck -acugm

The flags in this command tell quotacheck to create (c) a new control file for users (u) and groups (g) in all currently mounted file systems (a).

3. Type the following command and press Enter:

# quotacheck -avugm

Running the quotacheck command again without the create (c) flag populates the control files with the current usage information. The current usage reflects the blocks and files allocated to users (u) and groups (g) on all quota-enabled file systems (a) . By default, quotacheck won’t compute disk usage on mounted file systems. (If you’ve enabled quotas for the root file system [/], you can’t unmount that drive.) The -m flag forces quotacheck to inspect file systems that can’t be remounted in read-only mode.

That’s it! The quota files are created, populated, and ready to use.

Remember that systems vary. The preceding steps work great on our system (and should work well on most simple configurations), but if you need more information about command options that might suit your specific hardware configuration, check out the official documentation. Just enter info quotacheck at the command line for fast access to the online documentation.

Setting quotas

At this point, the quota tools have been installed, and the control files are in place (which we explain how to do in preceding sections). Now it’s time to impose quotas. Here, we explain how to set quotas for a user name or group and how to set the grace period for users who have met their quotas and need to clean up their files.

The default editor for quota is vi, a powerful but unfriendly editor. When you first set quotas, we recommend fixing up the quota editor a bit. Our editor of choice is kedit or kate. See the following steps to find out how.

To set quotas for a user, follow these steps:

1. Open a terminal window and give yourself superuser privileges with the su - command.

2. To change the default editor for quota, enter the following command:

# export EDITOR=$(which kedit)

If you prefer another editor, just substitute it for kedit in the preceding command.

3. To edit the control files and define quotas, enter the following command:

# edquota username

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edquota creates a temporary file that contains the current quota settings for username and then opens that file in the editor that you specified, as shown in Figure 21-2.

• Figure 21-2: The disk quota file.

The quota file that you see contains one line for each quota-enabled file system (the file system name is in the first column). edquota lets you control disk usage in 1024-byte blocks. You can also control the total number of files that a given user can create on a file system. (The quota tools all refer to inode quotas — inode is essentially a synonym for file.)

The numbers listed under blocks and inodes show disk space (and file count) currently used by the given user. A Linux quota is defined by three values:

Soft limit: This controls the maximum amount of space that you should use.

Hard limit: This controls the maximum amount of space that you can use.

Grace period: When you exceed the soft limit, Linux warns you and gives you a grace period. During the grace period, you can continue to accumulate more disk space (up to the hard limit). If, at the end of the grace period, you’re still over the soft limit, the soft limit becomes a hard limit.

For example, suppose your soft limit is 2GB, your hard limit is 2.5GB, and the grace period is one week. As soon as your disk usage exceeds 2GB, Linux displays a warning. You can exceed your soft limit for

one week (but you can never go above 2.5GB). After the grace period, you can’t create any new files (or write more data to existing files) until you clean up enough stuff to fall back to the 2GB soft limit. You can exceed the soft limit (for a week), but you can’t exceed the hard limit.

Deciding how many blocks or inodes a user needs is a matter of system resources. If users need access only to e-mail, they obviously need fewer files (and less disk space) than users doing development work. If you have plenty of room, you can allocate larger pieces of the total pie.

You can also assign quotas to a group of users. To assign group quotas, follow these steps:

1. Give yourself superuser privileges with the su - command.

2. To edit the control files and define the group quota, use the following command:

# edquota -g groupname

The -g indicates that the following name is the name of a group.

3. Edit the quotas as desired (following the same basic rules we discuss earlier in this section), and then save the file and close the editor.

Linux is far kinder than many people would be. If you exceed a soft limit, your files are still there (Linux doesn’t delete the extra data). You just don’t get any more space until you trim down a bit.

To set the grace period, enter the following command:

# edquota -t

The editor opens, displaying the current settings for the block and inode grace periods, as shown in Figure 21-3.