Use dd to write data starting from a specific location

Question

I want to use dd to write data starting from a specific location (basically skip the first 50000 bytes ) on a disk and start writing after the first 50000 bytes. I tried doing this ``` dd of=/dev/disk1 if=/dev/random seek=50000 ``` I let the above line run for few mins and then when I cancel it out, I get this ``` 0+6 records in 0+0 records out 0 bytes (0 B) copied, 79.2458 s, 0.0 kB/s ``` Looks to me nothing got copied. Am I doing anything wrong ?

Accepted Answer

From dd docs:

```
‘seek=n’

Skip n ‘obs’-byte blocks in the output file before copying. 
if ‘oflag=seek_bytes’ is specified, n is interpreted as a byte 
count rather than a block count. 
```

So it looks like you want this:

```
dd of=/dev/disk1 if=/dev/random obs=50000  seek=1
```

Or this:

```
dd of=/dev/disk1 if=/dev/random oflag=seek_bytes  seek=50000
```

Another thing is that `/dev/random` will block if kernel pool is empty. You can try `/dev/urandom` instead, which will use other methods to generate a number without blocking when the pool is empty:

```
dd of=/dev/disk1 if=/dev/urandom oflag=seek_bytes  seek=50000
```

Use dd to write data starting from a specific location

Solution

Problem