CODEWITHSUNDEEP
linuxbashunixdd
Abhishek Dave
Abhishek Dave

Reputation: 749

how to use dd to read and seek different block size

I have a situation where i have to read sparse file. This file is having data at specific offset. Now i want to achieve. 1) Read 3 blocks(custom sizes) from the given offset 2) offset need to be seek using 1M

So, i am trying below command but not successful. I am reading more contents for sure.

dd if=a_Sparse_file_ofSIZe_1024M of=/dev/null ibs=1M skip=512 obs=262144 count=3

skip 512M of blocks and read from 512M+1 th offset using block of 256K for 3 counts.

skip always should be in MBs and count blocks are variable. I am sure i am reading more data. Can someone please correct me.

Upvotes: 1

Views: 2172

Answers (2)

Mark Setchell
Mark Setchell

Reputation: 207425

You can always string 2 dds together, the first one to skip and the second one to read your actual data:

dd if=a_Sparse_file_ofSIZe_1024M bs=1M skip=N | dd bs=262144 count=3

Upvotes: 3

Marat Talipov
Marat Talipov

Reputation: 13304

The count parameter seems to be based on ibs, so the obs value does not matter here. As your obs value is four times smaller than ibs, I would suggest to set bs=256K and just multiply skip value by four: skip=2048.

Upvotes: 1

Related Questions