Kexecboot is a C program able to scan the partitions on available devices, offering a graphical framebuffer menu and allowing user to select from which one to boot. Specifically, kexecboot creates the command line for kexec.
Typically kexecboot resides together with kexec in a small initramfs, embedded in a custom-tailored kernel compiled with support for initramfs and kexec system call. Both binaries are built static, linked against klibc to optimize size. Kexecboot may be linked against other *libc (glibc, eglibc, uclibc) and may be used as standalone binary as well.
Initially the program has been developed for Sharp Zaurus PDA (armv5te). For the machines of that family there is specific code reading bootparams directly from NAND, circumventing the obsolete bootloader which is incompatible with modern 2.6.x kernels.
Kexecboot is free software. You can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.
Flashed on NAND and launched as first kernel by the original bootloader, this solution gives following advantages:
- multi machine support: we build for many architectures using OpenEmbedded (tested on arm, mipsel and x86/x86_64)
- zImage and uImage (for arm and sh) support
- easy customization: just add machine-specific workarounds (see Zaurus raw read of bootparams from NAND)
- small size: complete linux-kexecboot_2.6.x image (initramfs + kernel) is about 1Mb (less with lzma patches)
- easy boot choice: boot from SD/CF/NAND/… even if bootloader doesn't support it
- multiple fs detection: we support many filesystems e.g. ext2/3/4, jffs2, reiserfs, vfat and more (ubifs is work in progress)
- kernel upgrade: no need to flash the device (kernel is in /boot of removable media)
- rapid testing: different distributions can live in separate partitions on the same device
Thus, kexecboot is an interesting solution for embedded linux distributions, which can just rely on kexecboot whithout having to consider what the real bootloader can and cannot do.