New answers tagged compression
Many of the compressors take an an environment variable to accept options that cannot be passed on the command line. In your case GZIP_OPT=-9 sort --compress-program=/bin/gzip The same is true for xz with XZ_OPT and bzip2 with BZIP2
If you have e2fsprogs 1.42.9, then you can use e2image to create the partition image without the free space in the first place, so you can skip the zeroing step.
You can use sfill. It's a better solution for thin volumes.
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