Create a big file

[mister_v]

Hi,

I want to create a big file 20G,
I tired it with fallocate, but it didn't work:

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fallocate -l 20G /path/file
fallocate failed: Operation not supported

Does any one know how to do it?
I want to create a file container to use with dm-crypt.

[Chris]

If sparse files are ok for you,
Like in your case: you want to create an image in order to populate it with a file system.

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dd if=/dev/zero of=/path/file bs=1G seek=20 count=0

If you check it with ls, you'll see its real size is 0 Bytes

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ls -lsh

You can now create th crypto container for dm-crypt

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cryptsetup -y luksFormat /path/file

Open it:

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cryptsetup luksOpen /path/file volume1

and create the flie-system

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mkfs.ext4 -j /dev/mapper/volume1

after that you can mount it and use it

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mount /dev/mapper/volume1 /mnt/crypto