ubiupdatevol should take the '-t' option without an additional argument like the help message states correctly. But when using it in that matter busybox gives an error message. root@OpenWrt:/# ubiupdatevol /dev/ubi1_0 -t ubiupdatevol: option requires an argument -- 't' BusyBox v1.22.1 (2015-05-27 14:11:07 CEST) multi-call binary. Usage: ubiupdatevol UBI_DEVICE [-t | [-s SIZE] IMG_FILE] Update UBI volume -t Truncate to zero size -s SIZE Size in bytes to resize to root@OpenWrt:/# ubiupdatevol -t /dev/ubi1_0 BusyBox v1.22.1 (2015-05-27 14:11:07 CEST) multi-call binary. Usage: ubiupdatevol UBI_DEVICE [-t | [-s SIZE] IMG_FILE] Update UBI volume -t Truncate to zero size -s SIZE Size in bytes to resize to