Busybox – How to Check Busybox Version

The reason that switch_root is not working on the command line is this code in busybox:

    if (st.st_dev == rootdev || getpid() != 1) {
        // Show usage, it says new root must be a mountpoint
        // and we must be PID 1
        bb_show_usage();
    }

You are not PID 1, so you are falling through into this bb_show_usage. The implication is that the switch_root command in your initramfs init script should run switch_root with exec. i.e.

exec switch_root ...

The other issue with your "not found" errors is likely because the shared libraries needed by the executables are not found, because the initramfs root filesystem does not have them. If you can get switch_root to work with exec, then is likely the "not found" error will go away.

The options that the BusyBox commands have depends a lot on the options that BusyBox is compiled with. BusyBox aims to be highly configurable so that very small cut down versions can be compiled for systems where resources are very limited. Larger, more full featured versions can be built where this isn't an issue.

In your case cpio needs the -p or --pass-through (long form) option enabled. Normally cpio behaves more like an archive utility like tar, however it also has an extra function which allows it to copy files. To enable this in BusyBox, it needs to be built with FEATURE_CPIO_P defined (also LONG_OPTS for long form options to be enabled for any program).

From your last question, I strongly recommend that you use rsync for what you are doing. You are probably better off asking another question detailing exactly what you are doing with rsync and why it doesn't do what you expect. rsync is an extremely versatile tool and can no doubt be configured to do what you want.

That said, you could try the following with cpio, this will create an archive and then extract it again (somewhat less efficient, but still the same result):

find . -mtime -2 | cpio -o | { cd /media/USB_FLASH_2 && cpio -imd; }

Unfortunately the -o option can also be disabled in BusyBox (FEATURE_CPIO_O build option), so this may not work either.

Update

Based on this line of output, you need to add an extra option when creating an archive:

    -o      Create (requires -H newc)

This changes the command to:

find . -mtime -2 | cpio -oH newc | { cd /media/USB_FLASH_2 && cpio -imd; }

This time I have tested with the cpio in the BusyBox for my own system and it works for me, however in some cases the mtimes for directories won't be preserved. rsync should be the best way to do this.