[X Newbies] Disk First Aid [was Re: [X Newbies] MacJanitor]

Florin Alexander Neumann alexn at ica.net
Tue Jul 29 07:25:00 PDT 2003

On Monday, Jul 28, 2003, at 14:01 Canada/Eastern, Randy B. Singer wrote:

> Mark Gibson said:
>> The startup disk is repaired automatically, if required, as part of
>> the startup process.
> No it isn't.

True, but not the whole story. Here's how it works in Jaguar. After a 
successful startup, mounted drives are marked "dirty". When a drive is 
legitimately dismounted (e.g., by ejecting it from the desktop or 
during shut-down), it is marked "clean". At startup, disks are checked 
for this parameter; when a "dirty" disk is found, fsck is called up to 
check it and attempt to repair it, if necessary. (Which, basically, is 
an idea you're already familiar with from Windows or Mac OS 8 or 9.) On 
the other hand, as Randy pointed out, a Safe Boot calls fsck to check 
disks regardless of their "dirty" status. Note that the "clean" status 
doesn't mean the disk has no errors -- it just means it was mounted and 
dismounted according to proper procedure.

On Monday, Jul 28, 2003, at 16:24 Canada/Eastern, Peter Sealy wrote:

> in the instructions window of the First Aid tab of Disk Utility app 
> [OS X 10.2.6] it says "The startup disk was verified, and repaired if 
> necessary, at boot time."

It is indeed ambiguous and therefore misleading. "Verified" can mean 
"checked to see if the 'dirty' bit was set" or "called fsck to check 
the disk".

> I do understand that you can not run DFA on the startup disk once the 
> startup process has completed

To summarize point already made, in Jaguar Disk Utility has two 
verify/repair functions on the Disk First Aid tab.

(1) Verify/Repair Disk can be performed on any disk that can be 
dismounted (I'm simplifying a little). The boot disk or a disk with 
open files can't be dismounted, therefore it won't work on them. To 
verify/repair a boot disk the user must either, (a) boot in a different 
mode (i.e., Safe Mode, which will make fsck run automatically, or 
Single-User Mode, where fsck can be run manually), or (b) boot from a 
different copy of the OS X system on another volume (i.e., another 
partition on the same drive, another internal drive, an external drive, 
or the OS X Install CD or DVD).

(2) Verify/Repair Permissions can be performed only on bootable 
volumes, i.e., volumes which have a copy of Mac OS X installed, 
including the current boot volume. There is a caveat here. This 
function shouldn't be run on volumes which contain copies of Mac OS X 
more recent than the one on the current boot volume, because it may 
generate errors. So, if the internal hard disk has Mac OS X v10.2.6, 
and the computer is booted from the Mac OS X v10.2.3 CD-ROM or DVD-ROM, 
running Verify/Repair Permissions is not a good idea; it's better to 
run it when booted from the internal disk.

A final point on terminology. Some people may not be aware that there 
is a distinction between "disk" and "disc". "Disk" refers to magnetic 
media (e.g., hard disks, floppy, Zip disks); "disc" refers to optical 
media (e.g., CD-ROM, CD-RW). Unfortunately, this linguistical subtelty 
is -- like the proper capitalization of titles -- all too often 
ignored, but Apple still uses it.


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