An ISO image or .iso file contains the disk image of an ISO 9660 file system, which is used for storing data on CD-ROMs and DVD-ROMs. It is possible to take an ISO image and record it onto a CD or DVD using various applications for doing so, and it is also possible to mount the ISO image using Linux, so that you can access the files without having to actually burn it to disk first.
ISO images downloaded from the Internet typically contain operating system installation software, such as installing Linux (eg Fedora, Ubuntu, openSUSE, Mandriva, CentOS etc) or BSD (eg FreeBSD, OpenBSD and NetBSD). Sometimes you might need to access files on these ISO images but don’t want to actually waste a disk just to access them.
Mounting an ISO image on Linux is as simple as this, running the command from a terminal either as root or using sudo:
mount -t iso9660 -o loop /path/to/filename /mnt/loop0
The /path/to/filename in the above example would be the path to and filename of the ISO image, eg /home/chris/temp/CentOS-5.1-i386-bin-1of6.iso, and /mnt/loop0 at the end of the command is a place to mount the file to and must be a directory that actually exists. If it does not exist, then you’ll get an error message like this:
mount: mount point /mnt/loop0 does not exist
I’m just using /mnt/loop0 as an example, but you could make it any directory that you would like to mount it to, as long as it exists.
After the ISO image has been successfully mounted, it’s just like accessing any directory on your regular filesystem, only it is read only and none of the files can be modified. For example, doing this:
ls -l /mnt/loop0
will display the directory listing of the ISO image mounted at /mnt/loop0 that we have mounted in the earlier example above. In the example of the CentOS 5.1 CD, the listing would look like this:
drwxr-xr-x 2 root root 86016 2007-11-25 08:36 CentOS -rw-r--r-- 7 root root 212 2007-03-30 13:50 EULA -rw-r--r-- 7 root root 18009 2007-03-10 18:01 GPL drwxr-xr-x 4 root root 2048 2007-11-25 08:31 images drwxr-xr-x 2 root root 2048 2007-11-25 08:31 isolinux drwxr-xr-x 2 root root 8192 2007-11-25 08:31 NOTES -rw-r--r-- 2 root root 655 2007-11-24 12:46 RELEASE-NOTES-cs -rw-r--r-- 2 root root 1401 2007-11-24 12:46 RELEASE-NOTES-cs.html -rw-r--r-- 2 root root 839 2007-11-24 12:46 RELEASE-NOTES-de -rw-r--r-- 2 root root 1571 2007-11-24 12:46 RELEASE-NOTES-de.html -rw-r--r-- 2 root root 694 2007-11-24 12:46 RELEASE-NOTES-en -rw-r--r-- 2 root root 1367 2007-11-24 12:46 RELEASE-NOTES-en.html -rw-r--r-- 2 root root 788 2007-11-24 12:46 RELEASE-NOTES-es -rw-r--r-- 2 root root 1619 2007-11-24 12:46 RELEASE-NOTES-es.html -rw-r--r-- 2 root root 852 2007-11-24 12:46 RELEASE-NOTES-fr -rw-r--r-- 2 root root 1641 2007-11-24 12:46 RELEASE-NOTES-fr.html -rw-r--r-- 2 root root 766 2007-11-24 12:46 RELEASE-NOTES-ja -rw-r--r-- 2 root root 1565 2007-11-24 12:46 RELEASE-NOTES-ja.html -rw-r--r-- 2 root root 706 2007-11-24 12:46 RELEASE-NOTES-nl -rw-r--r-- 2 root root 1433 2007-11-24 12:46 RELEASE-NOTES-nl.html -rw-r--r-- 2 root root 752 2007-11-24 12:46 RELEASE-NOTES-pt_BR -rw-r--r-- 2 root root 1480 2007-11-24 12:46 RELEASE-NOTES-pt_BR.html -rw-r--r-- 2 root root 801 2007-11-24 12:46 RELEASE-NOTES-ro -rw-r--r-- 2 root root 1473 2007-11-24 12:46 RELEASE-NOTES-ro.html drwxr-xr-x 2 root root 2048 2007-11-25 09:07 repodata -rw-r--r-- 7 root root 1512 2007-03-10 18:01 RPM-GPG-KEY-beta -rw-r--r-- 2 root root 1504 2007-02-20 06:57 RPM-GPG-KEY-CentOS-5 -r--r--r-- 1 root root 6360 2007-11-25 09:07 TRANS.TBL
To unmount the ISO image when you are done, simply do this, running the command from a terminal either as root or using sudo:
umount /mnt/loop0
If you didn’t run it as root or using sudo, then you’ll see an error similar to this:
umount: /mnt/loop0 is not in the fstab (and you are not root)
Just run it again using sudo or as the root user and it should work fine.
Mounting more than one ISO image at the same time
If you need to have more than one ISO image mounted at the same time so you can reference files on several ISO images at once, then just mount each one using a different /dev/loopX and different mount location. For example, to mount all 6 of the CentOS CD images used in the above example, you would do the following.
First of all make sure the directories we are going to mount them to have been created (we’ll mount CD 1 at /mnt/loop1, CD 2 at /mnt/loop2 and so on, so as not to cause confusion):
mkdir /mnt/loop1 mkdir /mnt/loop2 mkdir /mnt/loop3 mkdir /mnt/loop4 mkdir /mnt/loop5 mkdir /mnt/loop6
Using a little bit of BASH magic we can simplify the above to this:
for i in 1 2 3 4 5 6; do mkdir /mnt/loop$i; done
And then mount each one. The following assumes we are in the same directory location as the ISO image files.
mount -t iso9660 -o loop CentOS-5.1-i386-bin-1of6.iso /mnt/loop1 mount -t iso9660 -o loop CentOS-5.1-i386-bin-2of6.iso /mnt/loop2 mount -t iso9660 -o loop CentOS-5.1-i386-bin-3of6.iso /mnt/loop3 mount -t iso9660 -o loop CentOS-5.1-i386-bin-4of6.iso /mnt/loop4 mount -t iso9660 -o loop CentOS-5.1-i386-bin-5of6.iso /mnt/loop5 mount -t iso9660 -o loop CentOS-5.1-i386-bin-6of6.iso /mnt/loop6
And using a little BASH magic again, we can simplify this as follows:
for i in 1 2 3 4 5 6; do mount -t iso9660 -o loop CentOS-5.1-i386-bin-$iof6.iso /mnt/loop$i; done
That will mount all 6 CD images to /mnt/loop0 through /mnt/loop6 . Note that the after $i is required, otherwise the for loop will think the variable name is $iof6. Escaping the o like $io fixes this.
Updated February 19th 2008
Thanks to Isaac Emesowum for letting me know that you don’t need to specify the "ro" option or the actual loop device because the system will assign it automatically, and will notify you if it runs out of loop devices. I have updated the above mount command examples accordingly.
Another update on February 19th…
I was just mounting an ISO image to checksum the contents just now, and decided to try not specifying the "-t iso9660" and that worked, so it looks like the mount command is smart enough to work out that it’s a CD image. This simplifies the mount command to this:
mount -o loop filename.iso /mnt/location