Can't change permissions on external

[surlygrl]

Disclaimer: I'm not the most tech savvy person around, but I'm pretty good at following instructions.

I'm really hoping someone can help me with this, as I sense my iMac is about to eat it and the most recent Time Machine backup I have is a few days ago. I'm backing up to an online service as we speak, but it may take a few days to finish and I'm not sure I have that sort of time...

For some reason, I suddenly can't write to my external HD. Time Machine won't acknowledge its existence, despite the fact that I can see it on my desktop. (Clearly there are issues here.) When I go to the "Get Info" screen, it tells me I have read only access. I click the lock, put in my admin password, and still have no option to change the permissions.

Here's me:

[trevor]

Open up your Terminal (it's found in /Applications/Utilities).

Copy the following from this forum, and paste it into Terminal:

ls -alOe /Volumes
diskutil list
id
echo "done"

Then copy/paste everything back here for us to see.

Trevor

[ganbustein]

When you say "Time Machine won't acknowledge its existence", do you mean "Time Machine won't back up to it" or "Time Machine won't back it up".

If you've been backing up to it, and suddenly you can't, it's (probably) not a permissions problem. Time Machine runs as root, and controls permissions on its backup extremely zealously. What may help is to go to TM's preference pane and use "Select Disk" to select the disk again, even if it appears to be already selected.

If you mean Time Machine won't back it up, I submit that that's usually a good thing. You don't want Time Machine backing up any partition that is not always mounted. The reason is, that if it's ever unmounted when Time Machine goes to back it up, TM will simply make note of that in the backup. The next time TM tries to back up and notices that the volume is present, it'll copy every file that's new since last time. Which is to say, every file, since "last time" no files were present. Backing up a volume that's sometimes mounted and sometimes not can chew up a lot of backup disk space very quickly. TM assumes that any external that is not your boot volume can be unmounted at any time, and so automatically excludes such volumes by default.

If, despite that, you do want TM to back up a partition on an external disk, open System Preferences→Time Machine→Options and remove the volume from the exclusions list. After doing that, be very careful that it's always mounted whenever TM is running.

If you're not backing up to it, nor backing it up, and your real issue is just that suddenly you can only read, it's probable that you "enabled ownership" on the volume. By default, ownership is disabled on external volumes that are not your boot volume nor your TM backup volume. The effect is that such an external acts like a very large floppy, suitable for sneaker-netting files between computers. Since ownership of a file is based on numeric userid, and these userids are not coordinated in any way between different computers, ownership doesn't make sense on disks that move between different computers.

To disable ownership on the volume, Get Info on it, and put a checkmark in front of "Ignore ownership on this volume". Do that on every computer (indeed, every boot volume) that will see the volume. (It will already be checked on any computer that has never seen the volume. The setting is saved independently on each boot volume that sees the disk, not on the disk itself, which is why each viewer needs to be told the desired setting.)

If you don't want to disable ownership, proceed as suggested by Trevor.

[surlygrl]

Quote: Originally Posted by ganbustein When you say "Time Machine won't acknowledge its existence", do you mean "Time Machine won't back up to it" or "Time Machine won't back it up".

I mean Time Machine won't back up to it. I had Time Machine set up to routinely back up my iMac to my external. It suddenly stopped. Coincidentally (or likely not), Spotlight started indexing endlessly until I unmounted the external HD and "hid" my user profile from Spotlight.

My machine is doing a variety of other funky things that has me suspecting it needs serious help. I remounted the external HD to see if I could get Time Machine to do a backup before I wipe the machine, and Time Machine isn't showing the external is mounted. I can't select it as a disk to back up to - it doesn't even appear as an option. It does appear on my desktop as being mounted, however, so I went to drag and drop files into it and that's when I discovered the permissions issue.

I'm positive I haven't done anything - manually, anyway - to the permissions as I never touch the thing. It just does its thing with Time Machine. This is the first time I've so much as clicked on its icon in over 6 months.

Quote: To disable ownership on the volume, Get Info on it, and put a checkmark in front of "Ignore ownership on this volume".

Another puzzler - I don't see where that's an option when I Get Info.

[surlygrl]

Quote: Originally Posted by trevor Open up your Terminal (it's found in /Applications/Utilities). Copy the following from this forum, and paste it into Terminal: ls -alOe /Volumes diskutil list id echo "done" Then copy/paste everything back here for us to see. Trevor

Thanks, Trevor. This is what it comes back with:

Last login: Thu May 24 00:17:43 on ttys000
Ambers-iMac:~ Amber$ ls -alOe /Volumes
total 8
drwxrwxrwt@ 4 root admin hidden 136 May 24 00:21 .
0: group:everyone deny add_file,add_subdirectory,directory_inherit,only_inherit
drwxrwxr-x 34 root wheel - 1224 May 23 14:53 ..
drwxrwxr-x 14 Amber staff - 544 Jan 14 14:57 STEFF_BKUP
lrwxr-xr-x 1 root admin - 1 May 23 14:51 c -> /
Ambers-iMac:~ Amber$ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS c 499.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI 209.7 MB disk1s1
2: Apple_HFS STEFF_BKUP 999.8 GB disk1s2
Ambers-iMac:~ Amber$ id
uid=501(Amber) gid=20(staff) groups=20(staff),402(com.apple.sharepoint.group.1),401(com.apple.access_screensharing),12(everyone),33(_appstore),61(loc alaccounts),79(_appserverusr),80(admin),81(_appserveradm),98(_lpadmin),100(_lpoperator),204(_developer)
Ambers-iMac:~ Amber$ echo "done"

[ganbustein]

Thanks for the clarification re: Time Machine.

The "Ignore ownership..." option does not apply to a Time Machine backup volume nor to your current boot volume, and won't even appear in Get Info for those volumes. (It's the bottom line of the Sharing & Permissions subpanel for other volumes.)

The output you show for Trevor's commands looks perfectly normal. There's no indication there why you (or Time Machine) wouldn't be able to write to it.

That suggests two next steps:

a) Have you tried restarting your computer? You don't mention it, and it's amazing how often this simple step can cure the most bizarre symptoms. (It's also amazing how often this simple step is simply overlooked.)

b) Permissions aren't the only thing that can make a disk unwritable. It may have been (or become) mounted read-only. Or a hardware write-protect switch may have become engaged. Show us the output from:

diskutil info /Volumes/STEFF_BKUP

(I'm especially interested in the "Read-Only Media" and "Read-Only Volume" lines, near the bottom of the output. If they both say "No", show us the whole output.)

It might be worth seeing what Time Machine thinks it's doing. Show us the output from:

tmutil machinedirectory

(tmutil is Lion-only. If you're not running Lion, tell us what you are running.)

[surlygrl]

Thanks. Yes, I've turned it off and back on many times over the past few days. After my computer's performance today, I'm 99.9% certain it's the problem - not the external. It's a big mess. I'm going to wipe it this weekend and hope that solves the problem.