dd command

[danielemazza]

Hi
Could someone explain better the option seek and bs in this command?
dd if=test_file.bin of=/dev/sdb1 bs=1024 seek=8
Why "test_file.bin" has been correctly copied on /dev/sdb1(/dev/sdb1/ is extern sd device ex3 normaly mounted with the "mount command") but with "ls" command i am not able to see that file on the device?

Thanks in advance
Best

 

[captain-sensible]

bs is the chunks( in bytes) it writes at a time and if you also put in (seek at 8) then it means it will leave this space 1024x8 (for your settings) on the destination (of=) before it starts writing to that the destination. in other words, there will be a gap on the destination of 1042x 8 bytes before data is written i've used dd before say for doing a fedora iso to a stick using bs=8M setting that would be 819200 bytes but using 4M is not uncommon .if you don't use the bs option i think the default is 512 bytes at a time . I have no idea how long that would take if your doing a dd of say 3.5 gig to a stick , although i'm sure someone will tell you. Also there is no output from dd command until finished so you might be sitting there wondering is it working. i've read you can do this

dd if=/dev/sdaxx  |pv| of=/dev/sdbxx

but i myself have not tried that

 

[Vrai]

Good question! It inspired me to look up information and learn something today

From the dd manpage:

seek=N skip N obs-sized blocks at start of output

From the www3.nd.edu site: https://www3.nd.edu/~pbui/teaching/cse.20189.sp16/homework07.html

seek: This specifies how many blocks (if any) we should skip in the output file.

From a stackexchange question: https://unix.stackexchange.com/questions/108858/seek-argument-in-command-dd

obs=expr
Specify the output block size, in bytes, by expr (default is 512).

obs = output block size

 

[captain-sensible]

Good question! It inspired me to look up information and learn something today

From the dd manpage:


From the www3.nd.edu site: https://www3.nd.edu/~pbui/teaching/cse.20189.sp16/homework07.html


From a stackexchange question: https://unix.stackexchange.com/questions/108858/seek-argument-in-command-dd


obs = output block size

dd= "disk destroyer" if you get it wrong , its been a while but destination should be unmounted or is my memory going ?

 

[Vrai]

dd= "disk destroyer"

Hahaha!! Good one
I understand that perfectly. I get very nervous whenever I use the "dd" command and check my typing numerous times! And then check again!

 

[danielemazza]

Maybe i do not explain in right way...Any kind of copy of that file with the dd command i am not able to see it in the destination folder(sd usb or whatever).
What i am wronging?