UFS: The Root of All Evil 267 That may be good by Unix standards, but it’s not great. Modern file systems use journaling, roll-back, and other sorts of file opera- tions invented for large-scale databases to ensure that the information stored on the computer’s hard disk is consistent at all times—just in case the power should fail at an inopportune moment. IBM built this technology into its Journaling File System (first present in AIX V 3 on the RS/6000 workstation). Journaling is in USL’s new Veritas file system. Will journal- ing become prevalent in the Unix world at large? Probably not. After all, it’s nonstandard. Automatic File Corruption Sometimes fsck can’t quite put your file system back together. The follow- ing is typical:

268 The File System Date: Wed, 29 May 91 00:42:20 EDT From: curt@ai.mit.edu (Curtis Fennell)3 Subject: Mixed up mail To: all-ai@ai.mit.edu Life4 had, what appears to be, hardware problems that caused a number of users’ mailboxes to be misassigned. At first it seemed that the owner- ship of a subset of the mailboxes had been changed, but it later became clear that, for the most part, the ownership was correct but the name of the file was wrong. For example, the following problem occurred: -rw------- 1 bmh user 9873 May 28 18:03 kchang but the contents of the file ‘named’ kchang was really that of the user bmh. Unfortunately, the problem was not entirely consistent and there were some files that did not appear to be associated with the owner or the filename. I have straightened this out as best I could and reassigned ownerships. (A number of people have complained about the fact that they could not seem to read their mailboxes. This should be fixed). Note that I associated ownerships by using the file owner- ships and grep'ing for the “TO:” header line for confirmation I did not grovel through the contents of private mailboxes. Please take a moment to attempt to check your mailbox. I was unable to assign a file named ‘sam.’ It ought to have belonged to sae but I think I have correctly associated the real mailbox with that user. I left the file in /com/mail/strange-sam. The user receives mail sent to bizzi, motor-control, cbip-meet, whitaker-users, etc. Soon after starting to work on this problem, Life crashed and the par- tition containing /com/mail failed the file-system check. Several mailboxes were deleted while attempting to reboot. Jonathan has a list of the deleted files. Please talk to him if you lost data. Please feel free to talk to me if you wish clarification on this prob- lem. Below I include a list of the 60 users whose mailboxes are most likely to be at risk. 3Forwarded to UNIX-HATERS by Gail Zacharias 4“Life” is the host name of the NFS and mail server at the MIT AI Laboratory.