rainbow-run: 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/sbin/rainbow-run - from package: rainbow

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

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