http://www.dmp.com.tw/tech/os-xlinux/xlinux-manual-5.7.htm#_Toc259779171
Всего-то надо
# mount -o remount,rw / (mount root file system readable/writable)
# (use FTP to upload files...)
# sync (flush file system buffers)
# mount -o remount,ro / (mount root file system read only)
Или вот еще, там дальше интересней:
http://www.dmp.com.tw/tech/os-xlinux/xlinux-manual-5.7.htm#_Toc259779177
8.8. Modify RAM Disk Image
1. Decompress ramdisk.gz on your desktop Linux (assume /tmp).
2. # losetup /dev/loop0 /tmp/ramdisk
3. # mount /dev/loop0 /mnt
4. Do you job on /mnt.
5. # sync
6. # umount /mnt
7. # losetup -d /dev/loop0
8. # gzip -v9 /tmp/ramdisk
9. You get a new ramdisk.gz with your changes.
!! Конечно все это делать ОЧЕНЬ опасно.
И вот еще
http://www.dmp.com.tw/tech/os-xlinux/xlinux-manual-5.7.htm#_Toc259779168
/etc/init.d/rcS It will be run first and you can add your initial programs into it. We add statement assign our IP in this file.