rootstrap: 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/rootstrap - from package: rootstrap

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

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