How can I shorten the Linux boot time?

You can ..

• decrease the "press key to stop" timeout of your bootloader
• compile the kernel for your target architecture
• configure the kernel with minimal components (leave out all unneeded hardware drivers or filesystems and so on)
• enable the XIP (execute in place) option (if possible)
• disable kernel module support (each filesystem access needs a bit time)
• keep the initial ram disk (initrd) size as minimal as possible (this saves time during decompressing the initrd)
• configure the busybox with minimal components (enable tools that are really needed)
• avoid compiling static applications (using libraries increases the application start up performance)
• remove all unneeded daemons or applications from your boot script
• avoid using a full blown shell (e.g. bash) (use a minimal shell like "ash")