gnatstub: command not found

Have You tried accessing the binary with the full path?

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/gnatstub - from package: asis-programs

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