bash: /sbin/reboot: Input/output error

Reference: http://www.linuxjournal.com/content/rebooting-magic-way

    # reboot
    bash: /sbin/reboot: Input/output error

The "magic SysRq key" provides a way to send commands directly to the kernel through the /proc filesystem. It is enabled via a kernel compile time option, CONFIG_MAGIC_SYSRQ, which seems to be standard on most distributions. First you must activate the magic SysRq option:

    echo 1 > /proc/sys/kernel/sysrq

When you are ready to reboot the machine simply run the following:

    echo b > /proc/sysrq-trigger