Download and use only OpenWrt firmware images ending in “-sysupgrade.bin” for command line upgrades.
For x86 systems there is no “sysupgrade” image, just be sure the new firmware image has the same family of filesystem as your old one. trap the cat
Note: upgrade files must be placed in /tmp, as the sysupgrade procedure unmounts flash storage during the upgrade process. If the upgrade file is not in /tmp, sysupgrade will NOT perform any upgrade and only reboot the system.