To most users, disc quotas will either be of no concern, or a fact of life that cannot be avoided. The quota(1) command will provide information on any disc quotas that may have been imposed upon a user.
There are two individual possible quotas that may be imposed, usually if one is, both will be. A limit can be set on the amount of space a user can occupy, and there may be a limit on the number of files (inodes) he can own.
Quota provides information on the quotas that have been set by the system administrators, in each of these areas, and current usage.
There are four numbers for each limit, the current usage, soft limit (quota), hard limit, and number of remaining login warnings. The soft limit is the number of 1K blocks (or files) that the user is expected to remain below. Each time the user's usage goes past this limit, he will be warned. The hard limit cannot be exceeded. If a user's usage reaches this number, further requests for space (or attempts to create a file) will fail with an EDQUOT error, and the first time this occurs, a message will be written to the user's terminal. Only one message will be output, until space occupied is reduced below the limit, and reaches it again, in order to avoid continual noise from those programs that ignore write errors.
Whenever a user logs in with a usage greater than his soft limit, he will be warned, and his login warning count decremented. When he logs in under quota, the counter is reset to its maximum value (which is a system configuration parameter, that is typically 3). If the warning count should ever reach zero (caused by three successive logins over quota), the particular limit that has been exceeded will be treated as if the hard limit has been reached, and no more resources will be allocated to the user. The only way to reset this condition is to reduce usage below quota, then log in again.
In most cases, the only way to recover from over quota conditions, is to abort whatever activity was in progress on the filesystem that has reached its limit, remove sufficient files to bring the limit back below quota, and retry the failed program.
However, if you are in the editor and a write fails because of an over quota situation, that is not a suitable course of action, as it is most likely that initially attempting to write the file will have truncated its previous contents, so should the editor be aborted without correctly writing the file not only will the recent changes be lost, but possibly much, or even all, of the data that previously existed.
There are several possible safe exits for a user caught in this situation. He may use the editor ! shell escape command to examine his file space, and remove surplus files. Alternatively, using csh, he may suspend the editor, remove some files, then resume it. A third possibility, is to write the file to some other filesystem (perhaps to a file on /tmp) where the user's quota has not been exceeded. Then after rectifying the quota situation, the file can be moved back to the filesystem it belongs on.