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Old 01-05-2006, 08:25 PM   #1
sarah_b
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Very Strange CD-RW Permission Behavior !


I have some CD-RW's with partimage images on them that I used for restoring a partition and it was successful. But I had some unrelated issues, so I reformatted the partition. But when I used the same CD-RW's the second time, the permission changed from read & execute to read only, which I thought was no big deal, I'll just change it back to read and execute. As owner, when I tried to put the check mark on execute, it told me that the permission could not be changed, it is a read only disk.

How can this be ? I had ownership and it was read & execute the day before, how could it have got changed to just read ? And seeing I have ownership, why could I not change it back to read & execute ?

Is it because I used CD-RW's ? I am wondering if anyone else has run onto this scenario and has an answer for me why this happened.

sarah
 
Old 01-05-2006, 09:31 PM   #2
Lenard
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You were mistaken, once the CD-RW media is written and at least the session is closed the file permissions are read only. Nothing strange and nothing got changed magically overnight. Check your /etc/fstab file for the drive entry, it should show the device as read only access (this is the normal setting).

http://www.tldp.org/HOWTO/CD-Writing-HOWTO.html ;see
4.9 How do I read/mount CD-ROMs with the CD-writer?
 
Old 01-05-2006, 09:45 PM   #3
sarah_b
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Quote:
Originally Posted by Lenard
You were mistaken, once the CD-RW media is written and at least the session is closed the file permissions are read only. Nothing strange and nothing got changed magically overnight.
Hi Lenard

In my case using the CD-RW for the image, when I got done with the burning, I checked the permission and read & execute were both checked. "I seen it with my own eyes"

I was just experimenting, I took an image I just created and copied it to my desktop, what happened was it changed owner from root to my_user_name. But it also removed the execute check mark and it will not let me (the owner) put it back.

Evidently the disk did not get closed, that may be the problem. I'm sure you know more about this than I do. But the one thing I do know (for me anyway), I was not able to restore the image with read only. When I have read and execute, then it will.

hmmmmm, what do you think ???
 
Old 01-05-2006, 10:00 PM   #4
sarah_b
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I used gnomebaker, I just checked it and I do not see a close disk option, so I just assumed it was closing it.

I also checked K3b, and that has an option to close the session, so from now on I will use it for images and see what happens.
 
Old 01-05-2006, 11:14 PM   #5
obnascar
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Quote:
Originally Posted by sarah_b
I checked the permission and read & execute were both checked.
I believe lenard was onto something when he said the disk needs to be closed.

But I do not believe one can restore an image to a partitions with read only rights. So I also tried one with read only and partimage give me errors: "the disk does not have permission"

Interesting, because I use CD-RW's all the time and do not have problems, but saying that, I do not remember of ever using the same CD-RW's twice though because mostly, I seldom ever have to use them for restoring a partition. But guess what ? I just did this week infact. I looked at them before I replied and they all have read & execute rights. I used K3b to close the session.
 
Old 01-06-2006, 07:53 AM   #6
Lenard
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Lets, try this again......

Once the data is written to the CD-R or CD-RW it cannot not be changed, this includes the permissions on the filesystem or for the individual files. It does not matter if the session is closed or not, it does not matter if the disc was finalized or not. It can be replaced, one needs to add a new session (multi-session) to replace the data (update the TOC for the changes*) or needs to blank the media (RW media only) and write the data fresh. Both write once (-R/+R media) and RW media support multi-session(s) as long as the media has space available for the new session(s) and the media is not finalized.

What was percieved by sarah_b more then likely was the un-sync'd information in the mountpoint. Once the media is unmounted or ejected the information is sync'd and updated, why the permissions seemed to change. This is why you saw read/write permissions after you 'burned' the media and changed the next time you mounted the media.

Yes, you need to have read/write permissions in order to copy/replace the data on the partition(s) from the CD media, but you do not need read/write permissions to read the data from the CD media, you only need read permissions.

Both gnomebaker and k3b are just GUI frontends to the CDR-Tools (cdrecord, cdrdao and others).

http://cdrecord.berlios.de/old/private/cdrecord.html
http://www.tldp.org/HOWTO/CD-Writing-HOWTO.html


* the old data is still in the earlier session unchanged, the TOC (Table of Contents) is updated to reflect the changes with the new session(s).
 
Old 01-06-2006, 10:56 AM   #7
sarah_b
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Lenard

Thanks for you latest reply and explanations.

What do you think then about partimage not letting me restore from the CD-RW images the second time ? What may I doing wrong or what could be causing this ? The path did not change and the file_name did not change. I still have the CD-RW disk, I haven't erased them yet.

Last edited by sarah_b; 01-06-2006 at 11:03 AM.
 
Old 01-06-2006, 01:16 PM   #8
Lenard
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Sorry no, I don't use partimage....just rsync my stuff to a NAS.
 
Old 01-06-2006, 03:33 PM   #9
sarah_b
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Quote:
Originally Posted by Lenard
Sorry no, I don't use partimage....just rsync my stuff to a NAS.
Thats ok, I'm going to be doing some playing around with it and see what I come up with....

I learned a lot from your post, thanks.....

sarah
 
  


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