istanbul: 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/istanbul - from package: istanbul

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

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