一般情况下reboot -nf就够了。如果还不够，就reboot -nff。reboot的文档(man reboot)：
-n, --no-sync
Don't sync hard disks/storage media before halt, power-off, reboot.
-f, --force
Force immediate halt, power-off, or reboot. When specified once, this
results in an immediate but clean shutdown by the system manager. When
specified twice, this results in an immediate shutdown without
contacting the system manager. See the description of --force in
systemctl(1) for more details.如果还不够，就直接向内核发sysrq:
echo 1 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger参考：
https://unix.stackexchange.com/questions/442932/reboot-is-not-working