mksunxiboot: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/mksunxiboot - from package: u-boot-tools

You may install the required package with command apt-get install {package}

Error in other languages:
mksunxiboot: bevel nie gevind nie
mksunxiboot: comandă negăsită
mksunxiboot: comando não encontrado
mksunxiboot: commande introuvable
mksunxiboot: command not found
mksunxiboot: käsku ei ole
mksunxiboot: không tìm thấy lệnh
mksunxiboot: komanda nerasta
mksunxiboot: Kommando nicht gefunden.
mksunxiboot: kommandot finns inte
mksunxiboot: komut yok
mksunxiboot: nie znaleziono polecenia
mksunxiboot: níor aimsíodh an t-ordú
mksunxiboot: no se encontró la orden
mksunxiboot: no s'ha trobat l'ordre
mksunxiboot: opdracht niet gevonden
mksunxiboot: parancs nem található
mksunxiboot: perintah tidak ditemukan
mksunxiboot: príkaz nenájdený
mksunxiboot: příkaz nenalezen
mksunxiboot: команда не найдена
mksunxiboot: командата не е открита
mksunxiboot: 命令找不到
mksunxiboot: コマンドが見つかりません