Mounting ULTRIX CDROMs on Linux

John-Paul Stewart jpstewart at
Thu May 20 15:11:18 CDT 2021

On 2021-05-20 4:01 p.m., Warner Losh via cctalk wrote:
> On Thu, May 20, 2021 at 1:56 PM Antonio Carlini via cctalk <
> cctalk at> wrote:
>> I'm running Linux Mint (an ubuntu derivative) and I want to mount ULTRIX
>> CDROM discs to see what I can see.
>> (I'm eventually going to image these, but I presume that will "just
>> work" with dd or ddrescue).
>> They are supposed to be UFS format (according to the net) and that
>> usually means you have to tell mount exactly which option to use (as not
>> all UFS implementations are compatible).
>> I've tried (all the options I can find) and failed:
>> $ sudo mount -t ufs  -o ufstype=44bsd /dev/sr1 /tmp/mount
> 44bsd is likely too new. ufstype=old or =sunos or =sun might work.

Setting ufstype=sun will indeed work for loopback mounting Ultrix CD images.

With physical CDs, the Linux CD-ROM driver expects the filesystem to use
2048 byte blocks but the UFS CDs have 512 byte blocks.  So you'll also
have to add "loop" to the options:

sudo mount -t ufs -o ro,ufstype=sun,loop /dev/sr1 /tmp/mount

That will mount the physical CD using a loopback device so you can
access the 512 byte per block filesystem.  (FWIW, I learned that trick
with IRIX EFS CDs, which have the same problem.)

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