This can be either a single cpio archive with a .cpio suffix or a space-separated list of directories and files for building the initramfs image. A cpio archive should contain a filesystem archive to be used as an initramfs image. Directories should contain a filesystem layout to be included in the initramfs image. Files should contain entries according to the format described by the "usr/gen_init_cpio" program in the kernel tree. When multiple directories and files are specified then the initramfs image will be the aggregate of all of them. See <file:Documentation/early-userspace/README> for more details. If you are not sure, leave it blank.
This setting is only meaningful if the INITRAMFS_SOURCE is contains a directory. Setting this user ID (UID) to something other than "0" will cause all files owned by that UID to be owned by user root in the initial ramdisk image. If you are not sure, leave it set to "0".
This setting is only meaningful if the INITRAMFS_SOURCE is contains a directory. Setting this group ID (GID) to something other than "0" will cause all files owned by that GID to be owned by group root in the initial ramdisk image. If you are not sure, leave it set to "0".
Support loading of a gzip encoded initial ramdisk or cpio buffer. If unsure, say Y.
Support loading of a bzip2 encoded initial ramdisk or cpio buffer If unsure, say N.
Support loading of a LZMA encoded initial ramdisk or cpio buffer If unsure, say N.
Support loading of a XZ encoded initial ramdisk or cpio buffer. If unsure, say N.
Support loading of a LZO encoded initial ramdisk or cpio buffer If unsure, say N.
This option decides by which algorithm the builtin initramfs will be compressed. Several compression algorithms are available, which differ in efficiency, compression and decompression speed. Compression speed is only relevant when building a kernel. Decompression speed is relevant at each boot. If you have any problems with bzip2 or LZMA compressed initramfs, mail me (Alain Knaff) <alain@knaff.lu>. High compression options are mostly useful for users who are low on RAM, since it reduces the memory consumption during boot. If in doubt, select 'gzip'
Do not compress the built-in initramfs at all. This may sound wasteful in space, but, you should be aware that the built-in initramfs will be compressed at a later stage anyways along with the rest of the kernel, on those architectures that support this. However, not compressing the initramfs may lead to slightly higher memory consumption during a short time at boot, while both the cpio image and the unpacked filesystem image will be present in memory simultaneously
The old and tried gzip compression. It provides a good balance between compression ratio and decompression speed.
Its compression ratio and speed is intermediate. Decompression speed is slowest among the four. The initramfs size is about 10% smaller with bzip2, in comparison to gzip. Bzip2 uses a large amount of memory. For modern kernels you will need at least 8MB RAM or more for booting.
The most recent compression algorithm. Its ratio is best, decompression speed is between the other three. Compression is slowest. The initramfs size is about 33% smaller with LZMA in comparison to gzip.
XZ uses the LZMA2 algorithm. The initramfs size is about 30% smaller with XZ in comparison to gzip. Decompression speed is better than that of bzip2 but worse than gzip and LZO. Compression is slow.
Its compression ratio is the poorest among the four. The kernel size is about 10% bigger than gzip; however its speed (both compression and decompression) is the fastest.