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diff --git a/share/doc/smm/04.quotas/quotas.ms b/share/doc/smm/04.quotas/quotas.ms new file mode 100644 index 00000000000..36918302518 --- /dev/null +++ b/share/doc/smm/04.quotas/quotas.ms @@ -0,0 +1,318 @@ +.\" Copyright (c) 1983, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)quotas.ms 8.1 (Berkeley) 6/8/93 +.\" +.EH 'SMM:4-%''Disc Quotas in a \s-2UNIX\s+2 Environment' +.OH 'Disc Quotas in a \s-2UNIX\s+2 Environment''SMM:4-%' +.ND 5th July, 1983 +.TL +Disc Quotas in a \s-2UNIX\s+2\s-3\u*\d\s0 Environment +.FS +* UNIX is a trademark of Bell Laboratories. +.FE +.AU +Robert Elz +.AI +Department of Computer Science +University of Melbourne, +Parkville, +Victoria, +Australia. +.AB +.PP +In most computing environments, disc space is not +infinite. +The disc quota system provides a mechanism +to control usage of disc space, on an +individual basis. +.PP +Quotas may be set for each individual user, on any, or +all filesystems. +.PP +The quota system will warn users when they +exceed their allotted limit, but allow some +extra space for current work. +Repeatedly remaining over quota at logout, +will cause a fatal over quota condition eventually. +.PP +The quota system is an optional part of +\s-2VMUNIX\s0 that may be included when the +system is configured. +.AE +.NH 1 +Users' view of disc quotas +.PP +To most users, disc quotas will either be of no concern, +or a fact of life that cannot be avoided. +The +\fIquota\fP\|(1) +command will provide information on any disc quotas +that may have been imposed upon a user. +.PP +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. +.PP +.I Quota +provides information on the quotas that have +been set by the system administrators, in each +of these areas, and current usage. +.PP +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. +.PP +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 \fBonly\fP way to reset this condition is +to reduce usage below quota, then log in again. +.NH 2 +Surviving when quota limit is reached +.PP +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. +.PP +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. +.PP +There are several possible safe exits for a user +caught in this situation. +He may use the editor \fB!\fP shell escape command to +examine his file space, and remove surplus files. +Alternatively, using \fIcsh\fP, 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. +.NH 1 +Administering the quota system +.PP +To set up and establish the disc quota system, +there are several steps necessary to be performed +by the system administrator. +.PP +First, the system must be configured to include +the disc quota sub-system. +This is done by including the line: +.DS +options QUOTA +.DE +in the system configuration file, then running +\fIconfig\fP\|(8) +followed by a system configuration\s-3\u*\d\s0. +.FS +* See also the document ``Building 4.2BSD UNIX Systems with Config''. +.FE +.PP +Second, a decision as to what filesystems need to have +quotas applied needs to be made. +Usually, only filesystems that house users' home directories, +or other user files, will need to be subjected to +the quota system, though it may also prove useful to +also include \fB/usr\fR. +If possible, \fB/tmp\fP should usually be free of quotas. +.PP +Having decided on which filesystems quotas need to be +set upon, the administrator should then allocate the +available space amongst the competing needs. How this +should be done is (way) beyond the scope of this document. +.PP +Then, the +\fIedquota\fP\|(8) +command can be used to actually set the limits desired upon +each user. Where a number of users are to be given the +same quotas (a common occurrence) the \fB\-p\fP switch +to edquota will allow this to be easily accomplished. +.PP +Once the quotas are set, ready to operate, the system +must be informed to enforce quotas on the desired filesystems. +This is accomplished with the +\fIquotaon\fP\|(8) +command. +.I Quotaon +will either enable quotas for a particular filesystem, or +with the \fB\-a\fP switch, will enable quotas for each +filesystem indicated in \fB/etc/fstab\fP as using quotas. +See +\fIfstab\fP\|(5) +for details. +Most sites using the quota system, will include the +line +.DS C +/etc/quotaon -a +.DE +in \fB/etc/rc.local\fP. +.PP +Should quotas need to be disabled, the +\fIquotaoff\fP(8) +command will do that, however, should the filesystem be +about to be dismounted, the +\fIumount\fP\|(8) +command will disable quotas immediately before the +filesystem is unmounted. +This is actually an effect of the +\fIumount\fP\|(2) +system call, and it guarantees that the quota system +will not be disabled if the umount would fail +because the filesystem is not idle. +.PP +Periodically (certainly after each reboot, and when quotas +are first enabled for a filesystem), the records retained +in the quota file should be checked for consistency with +the actual number of blocks and files allocated to +the user. +The +\fIquotacheck\fP\|(8) +command can be used to accomplish this. +It is not necessary to dismount the filesystem, or disable +the quota system to run this command, though on +active filesystems inaccurate results may occur. +This does no real harm in most cases, another run of +.I quotacheck +when the filesystem is idle will certainly correct any inaccuracy. +.PP +The super-user may use the +\fIquota\fP\|(1) +command to examine the usage and quotas of any user, and +the +\fIrepquota\fP\|(8) +command may be used to check the usages and limits for +all users on a filesystem. +.NH 1 +Some implementation detail. +.PP +Disc quota usage and information is stored in a file on the +filesystem that the quotas are to be applied to. +Conventionally, this file is \fBquotas\fR in the root of +the filesystem. +While this name is not known to the system in any way, +several of the user level utilities "know" it, and +choosing any other name would not be wise. +.PP +The data in the file comprises an array of structures, indexed +by uid, one structure for each user on the system (whether +the user has a quota on this filesystem or not). +If the uid space is sparse, then the file may have holes +in it, which would be lost by copying, so it is best to +avoid this. +.PP +The system is informed of the existence of the quota +file by the +\fIsetquota\fP\|(2) +system call. +It then reads the quota entries for each user currently +active, then for any files open owned by users who +are not currently active. +Each subsequent open of a file on the filesystem, will +be accompanied by a pairing with its quota information. +In most cases this information will be retained in core, +either because the user who owns the file is running some +process, because other files are open owned by the same +user, or because some file (perhaps this one) was recently +accessed. +In memory, the quota information is kept hashed by user-id +and filesystem, and retained in an LRU chain so recently +released data can be easily reclaimed. +Information about those users whose last process has +recently terminated is also retained in this way. +.PP +Each time a block is accessed or released, and each time an inode +is allocated or freed, the quota system gets told +about it, and in the case of allocations, gets the +opportunity to object. +.PP +Measurements have shown +that the quota code uses a very small percentage of the system +cpu time consumed in writing a new block to disc. +.NH 1 +Acknowledgments +.PP +The current disc quota system is loosely based upon a very +early scheme implemented at the University of New South +Wales, and Sydney University in the mid 70's. That system +implemented a single combined limit for both files and blocks +on all filesystems. +.PP +A later system was implemented at the University of Melbourne +by the author, but was not kept highly accurately, eg: +chown's (etc) did not affect quotas, nor did i/o to a file +other than one owned by the instigator. +.PP +The current system has been running (with only minor modifications) +since January 82 at Melbourne. +It is actually just a small part of a much broader resource +control scheme, which is capable of controlling almost +anything that is usually uncontrolled in unix. The rest +of this is, as yet, still in a state where it is far too +subject to change to be considered for distribution. +.PP +For the 4.2BSD release, much work has been done to clean +up and sanely incorporate the quota code by Sam Leffler and +Kirk McKusick at The University of California at Berkeley. |