Problem with dd and /dev/sr0

[Rick Stevens]

On 03/14/2016 10:23 AM, jd1008 wrote:
>
> On 03/14/2016 11:17 AM, Rick Stevens wrote:
>> On 03/14/2016 10:11 AM, jd1008 wrote:
>>> Hi all,
>>> time dd if=/dev/sr0 of=Our_Group_Picnic.iso bs=64M skip=5888
>>> conv=noerror,notrunc oflag=append
>>> dd: ‘/dev/sr0’: cannot skip: Invalid argument
>>> 0+0 records in
>>> 0+0 records out
>>> 0 bytes (0 B) copied, 0.000301689 s, 0.0 kB/s
>>>
>>> but
>>>
>>> {3464-jd at localhost}$ time dd if=/dev/sr0 of=Our_Group_Picnic.iso bs=64M
>>> conv=noerror,notrunc
>>>
>>> works just fine.
>>>
>>> So why is it that skip des not work on optical media?
>>
>> Skip works fine, but you must specify the units. "skip=5888" doesn't
>> tell dd how far to skip. E.g. "skip=5888c" would skip 5888 bytes. From
>> the man page:
>>
>>     N and BYTES may be followed by the following multiplicative
>>     suffixes: c=1, w=2, b=512, kB =1000, K=1024, MB=1000*1000,
>>     M=1024*1024, xM=M  GB=1000*1000*1000, G=1024*1024*1024, and
>>     so on for T, P, E, Z, Y.
> I thought that bs=64M  applies to all io for input and output, and skip.
> I did not specify ibs= nor obs=, just bs=

I've rarely used "ibs" and "obs" separately, just "bs". That being said,
I've always used the suffix with "skip".

It may be that "bs" does not set "ibs", so a "skip=5888" wouldn't have
the size. Don't know that for a fact, but it's possible. Stranger things
have been known to happen.
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
- AIM/Skype: therps2        ICQ: 226437340           Yahoo: origrps2 -
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-       A squeegee, by any other name, wouldn't sound as funny.      -
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