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cpio compress and extract

we often see a file is a *.cpio.gz, normally it is a gzip compressed data.

“gunzip file.cpio.gz” to extract it to a file.cpio, whichi is a ASCII cpio archive.

“cpio -ivmd < file.cpio” can extract it finally.

we can use “find . | cpio -o –format=newc > ../file.cpio” to compress a directory

to file.cpio. this command should be run in the root of the directory.

then we use “gzip -c file.cpio > file.cpio.gz” to get orignal gzip compressed file.

One initrd file system should be cpio.gz type. for example, we can run a qemu

besed on memory initrd file system like:

qemu-system-aarch64 -machine virt -cpu cortex-a57 \-m 300M \-kernel ~/repos/linux/arch/arm64/boot/Image \-initrd ~/rootfs/rootfs.cpio.gz \-append "console=ttyAMA0 root=/dev/ram rdinit=/init" \-nographic \

Note: as we run rootfs in memory, -m parametre above should carefully choose.

too small is a bad idear.

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