CODEWITHSUNDEEP
linuxpartitioning
Tango
Tango

Reputation: 669

How can I quickly erase all partition information and data on partitions in LInux?

I'm testing a program to use on Raspberry Pi OS. A good part of what it does is read the partitioning info on the system drive, which is going to be (in this case), /boot and / and no extra partitions, just the two. I'm using a Python script that calls sfdisk. I do what so many examples show: I get the info from the system drive, read it as output, then use it as input to run the command to format the target drive.

I'm using Python and doing this with subprocess.run(). The script I'm writing, when it writes the 2nd partition on the target drive, writes it as a small size, then I use parted to extend the partition to the end of the drive. In between tests, to wipe my data so I can start fresh, I've been using sfdisk to make one partition for the full size of the drive. Also, I'm using USB memory sticks at this point for testing. I'll generally be using that for drives or using SD cards.

The problem I'm finding is that the file structure is persistent on the partitions on the target drive. (All this paragraph is about ONLY the target drive.) If I divide it up into 2 partitions (as I need to use, eventually), I find that /boot, the small 1st partition, still has all the files from previous usage of the partition. If I've tried to wipe the information by making only one big partition on the drive, I still see only, in that one partition, the original files for the /boot partition. If I split it into 2 partitions, the locations are going to be the same as when I normally make a Raspbian image and I find the files in both /boot and the system drive are still there.

So repartitioning, with the partitions in the same location, leaves me with the files still intact from the previous incarnation of a partition in the same sectors.

I'd like to, for testing, just wipe out all the information so I start fresh with each test, but I do not want to just use dd and write gigabytes of 0s or 1s to the full drive to wipe out the data.

What can I do to make sure:

  1. The partition table is wiped out between tests
  2. Any directory structure or file information for the partitions is wiped out so there are no files still surviving on any partitions when I start my testing?

Upvotes: 0

Views: 1136

Answers (1)

sea0003
sea0003

Reputation: 94

A "nice" thing about linux filesystems is that they are separate from partition tables. This has saved me in the past when partition tables have been accidentally deleted or corrupted - recreate the partition table and the filesystem is still there! For your use case, if you want the files to be "gone", you need to destroy the filesystem superblocks. Destroying just the first one is probably sufficient for your use case.

Using dd to overwrite just the first MB of each of your filesystems should get you what you need. So, if you're starting your first partition/FS on block 0, you could do something like

# write 1MB of zeros to wipe out /boot
dd if=/dev/zero of=/dev/path_to_your_device bs=1024 count=1024

That ought to wipe out the /boot file system. From there you'll need to calculate the start of your root volume and you can use skip as per https://superuser.com/questions/380717/how-to-output-file-from-the-specified-offset-but-not-dd-bs-1-skip-n to write a meg of zeros at the start of your root filesystem.

Alternately, if /boot is small, you can just write sizeof(/boot)+1MB (assuming you start /root immediately after /boot) and it'll overwrite the primary superblock from /root too while saving you some calculations.

Note that the alternate superblocks will still exist, so at some point if you (or someone) wanted to get back what was there previously then recovery of alternate superblocks might be possible, except that whatever files were present in that first 1MB of disk would be corrupt due to overwrite.

Upvotes: 1

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