Managing Quotas (Tasks)
This chapter describes how to set up and administer quotas for disk space and inodes. This is a list of the step-by-step instructions in this chapter.
What Are Quotas?
Quotas enable system administrators to control the size of UFS file systems by limiting the amount of disk space and the number of inodes (which roughly corresponds to the number of files) that individual users can acquire. For this reason, quotas are especially useful on the file systems where user home directories reside. As a rule, public and /tmp file systems usually do not benefit as much from the establishment of quotas.
Setting up quotas involves these general steps:
Enable file system quotas by issuing a series of commands, ensuring that quotas are enforced each time the system is rebooted and the file system is mounted. Entries must be added to the /etc/vfstab file, and a quotas file must be created in the root of the file system.
After a quota is created for one user, the quota can be copied as a prototype to set up other user quotas.
Before quotas are turned on, another command checks for consistency by comparing the proposed quotas to the current disk usage to make sure there are no conflicts.
Finally, a command turns on the quotas for one or more file systems.
These steps ensure that quotas are automatically activated on a file system each time it is mounted. For step-by-step instructions, see Chapter 17, Managing Quotas (Tasks).
Once quotas are in place, they can be changed to adjust the amount of disk space or number of inodes that users can consume. Additionally, quotas can be added or removed as system needs change. For instructions on how to change quotas, disable individual quotas, or remove quotas from file systems, see "Changing and Removing Quotas".
Using Quotas
Using quotas enable system administrators to control the size of UFS file systems by limiting the amount of disk space and the number of inodes (which roughly corresponds to the number of files) that individual users can acquire. For this reason, quotas are especially useful on the file systems where user home directories reside.
Once they are in place, quotas can be changed to adjust the amount of disk space or number of inodes that users can consume. Additionally, quotas can be added or removed as system needs change. See "Changing and Removing Quotas" for instructions on changing quotas or the amount of time that quotas can be exceeded, disabling individual quotas, or removing quotas from file systems.
In addition, quota status can be monitored. Quota commands enable administrators to display information about quotas on a file system, or search for users who have exceeded their quotas. For procedures that describe how to use these commands, see "Checking Quotas".
Setting Soft Limits and Hard Limits for Quotas
You can set both soft and hard limits. The system will not allow a user to exceed his or her hard limit. However, a system administrator may set a soft limit (sometimes referred to as a quota), which the user can temporarily exceed. The soft limit must be less than the hard limit.
Once the user exceeds the soft limit, a timer begins. While the timer is ticking, the user is allowed to operate above the soft limit but cannot exceed the hard limit. Once the user goes below the soft limit, the timer is reset. However, if the user's usage remains above the soft limit when the timer expires, the soft limit is enforced as a hard limit. By default, the soft limit timer is set to seven days.
The timeleft field in the repquota and quota commands shows the value of the timer.
For example, let's say a user has a soft limit of 10,000 blocks and a hard limit of 12,000 blocks. If the user's block usage exceeds 10,000 blocks and the timer is also exceeded (more than seven days), the user will not be able to allocate more disk blocks on that file system until his or her usage drops below the soft limit.
The Difference Between Disk Block and File Limits
A file system provides two resources to the user: blocks (for data) and inodes (for files). Each file consumes one inode. File data is stored in data blocks (usually made up of 1 Kbyte blocks).
Assuming there are no directories, a user can exceed his or her inode quota by creating all empty files (without using any blocks). A user can also use one inode yet exceed his or her block quota by simply creating one file large enough to consume all the data blocks in the user's quota.
Setting Up Quotas
You can set up quotas to limit the amount of disk space and number of inodes (roughly equivalent to the number of files) available to users. These quotas are activated automatically each time a file system is mounted. This section describes how to configure file systems for quotas, and how to set up and activate quotas.
Setting up quotas involves these general steps:
A series of commands prepares a file system to accept quotas, ensuring that quotas will be enforced each time the system is rebooted and the file system is mounted. Entries must be added to the /etc/vfstab file, and a quotas file must be created in the top-level directory of the file system.
After a quota is created for one user, it can be copied as a prototype to set up other user quotas.
Before quotas are actually turned on, another command checks for consistency by comparing the proposed quotas with the current disk usage to make sure that there are no conflicts.
Finally, a command turns the quotas on for one or more entire file systems.
These steps ensure that quotas are automatically activated on a file system each time it is mounted. For specific information about these procedures, see "Setting Up Quotas (Task Map)".
The following table describes the commands you use to set up disk quotas.
Table 17-1 Commands for Setting Up Quotas
Command | Task | Man Page |
|---|---|---|
edquota | Sets the hard limits and soft limits on the number of inodes and the amount of disk space for each user | edquota(1M) |
quotacheck | Examines each mounted UFS file system, comparing the file system's current disk usage against information stored in the file system's disk quota file, and resolves inconsistencies | quotacheck(1M) |
Activates the quotas for the specified file systems | quotaon(1M) | |
quota | Displays users' disk quotas on mounted file systems to verify that the quotas have been correctly set up | quota(1M) |