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I have an ISO file and I mount it under /mnt/isofile. Then I copied this file to another folder. But the contents are read-only and belonged to root. I tried to use chmod and chown. But it prompts with the message:

it is read only file system.

What is going on here?

NOTE: There is a tar file in the .iso, I want to compress it, but failed with the same "read only file system" message.

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up vote 12 down vote accepted

ISO 9660 is by design a read-only file system. This means that all the data has to be written in one go to the medium. Once written, there is no provision for altering the stored content. Therefore ISO 9660 is not suitable to be used on random-writable media, such as hard disks.

You need to copy whole directory tree to another directory, make your changes and then burn a new image.

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What makes the format so difficult to modify? – Ciro Santilli 巴拿馬文件 六四事件 法轮功 May 22 '15 at 9:12

If you happen to run an OS supporting it (Linux & BSDs), you might use Unionfs to somewhat mount an ISO in read-write mode. All writes will be actually be done on a read-write file system but depending on your needs, that might fit them.

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