Mounting ULTRIX CDROMs on Linux

John-Paul Stewart jpstewart at
Tue Jul 27 14:02:55 CDT 2021

On 2021-07-26 9:34 a.m., Maciej W. Rozycki via cctalk wrote:
> On Fri, 21 May 2021, Maciej W. Rozycki wrote:
>>  ISTR upstreaming some fixes to Linux UFS support 20+ years ago to address 
>> this very problem (IIRC OSF/1 or Digital Unix CD-ROMs were also UFS, and I 
>> had a need to access them under Linux for some reason) and with them in 
>> place I thought the loop device hack was not needed anymore.
>>  Perhaps my memory tricks me or something has since regressed though, e.g. 
>> due to changes in the block layer, so I'll try to remember to see what's 
>> happened here when I get to my Ultrix CDs when I'm in my remote lab next 
>> time.  It's not a feature that's used on a regular basis after all, so any 
>> regression can be long-lived.
>  I remembered right.  An old Linux 2.4.26 kernel binary mounts a UFS CD 
> here using the old IDE hardware driver just fine with no need for block 
> size translation via the loop device:
> # mount -t ufs -o ro,ufstype=old /dev/hdc /mnt/cdrom
> # mount | grep ufs
> /dev/hdc on /mnt/cdrom type ufs (ro,ufstype=old)
> # uname -a
> Linux (none) 2.4.26 #8 SMP Sat Aug 14 21:00:06 CEST 2004 i586 unknown unknown GNU/Linux
> # 
> Not anymore with Linux 2.6.18 or anything newer:
> # mount -t ufs -o ro,ufstype=old /dev/hdc /mnt/cdrom
> mount: wrong fs type, bad option, bad superblock on /dev/hdc,
>        or too many mounted file systems
> # dmesg | tail -n 1
> UFS: failed to set blocksize
> # mount -t ufs -o loop,ro,ufstype=old /dev/hdc /mnt/cdrom
> # mount | grep ufs
> /dev/hdc on /mnt/cdrom type ufs (ro,loop=/dev/loop0,ufstype=old)
> # uname -a
> Linux (none) 2.6.18 #9 SMP Sun Nov 26 18:31:10 GMT 2017 i586 unknown unknown GNU/Linux
> # 
> So we do have a regression here, sigh.  

Thanks for the analysis.  I would have speculated that the difference
was in the SCSI CD-ROM driver for /dev/sr* devices since those are what
are used in modern Linux distributions.  But your results quite clearly
show that's not the case.  It also shows just how long ago the change
happened.  Very interesting.

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