Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.unix Subject: Re: /tmp and /usr/tmp Message-ID: <3661@utzoo.UUCP> Date: Mon, 19-Mar-84 19:36:46 EST Article-I.D.: utzoo.3661 Posted: Mon Mar 19 19:36:46 1984 Date-Received: Mon, 19-Mar-84 19:36:46 EST References: <4432@amd70.UUCP>, <3566@utcsrgv.UUCP>, <137@uthub.UUCP> Organization: U of Toronto Zoology Lines: 33 Brian is close. As I understand it, the reason for the /tmp-/usr/tmp split is identical to the reason for the /bin-/usr/bin and /lib-/usr/lib splits, and is a historical accident of hardware configuration at the Research system. At one time (circa the time of the original Unix paper in CACM), the Research machine was a 45 with a fixed-head disk, some RK05s, and an RP03. The root went on the fixed-head disk, since the absence of seek times made it fast. But fixed-head disks (anybody remember them?) were *tiny*. Two megabytes [sic] was a big fixed-head disk. So you had to be fairly careful to avoid overflowing the root file system (which included /tmp -- it wasn't a separate filesystem). /usr, on the other hand, was the main filesystem on the 40-MB RP03. So you had a very sharp split of hardware: things directly under "/", like /tmp, /bin, and /lib, were fast but had to be small; things under /usr could be big but accesses to them were slower. So you put the heavily-used commands in /bin, the heavily-used libraries in /lib, and [flourish of trumpets] the small temporary files in /tmp. All the other slush went under /usr, including a /usr/tmp directory for big temporaries. This is why a few programs like sort(1) put their temporaries in /usr/tmp: they expect them to be big. In practice, fixed-head disks are historical relics now, and much of the justification for the various /x-/usr/x splits has disappeared. There is one reason why you might retain a /tmp-/usr/tmp split, however. If your /tmp filesystem is kept in "RAM disk" or something similar for speed, you might want to keep your editor tempfiles somewhere else if your editor has crash recovery. Crash recovery definitely works better when the files it is looking for are kept in non-volatile memory! -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry