mkuserimg: 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/mkuserimg - from package: android-tools-fsutils

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

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