s9advgen: 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/s9advgen - from package: scheme9

You may install the required package with command apt-get install {package}
Error in other languages:
s9advgen: bevel nie gevind nie
s9advgen: comandă negăsită
s9advgen: comando não encontrado
s9advgen: commande introuvable
s9advgen: command not found
s9advgen: käsku ei ole
s9advgen: không tìm thấy lệnh
s9advgen: komanda nerasta
s9advgen: Kommando nicht gefunden.
s9advgen: kommandot finns inte
s9advgen: komut yok
s9advgen: nie znaleziono polecenia
s9advgen: níor aimsíodh an t-ordú
s9advgen: no se encontró la orden
s9advgen: no s'ha trobat l'ordre
s9advgen: opdracht niet gevonden
s9advgen: parancs nem található
s9advgen: perintah tidak ditemukan
s9advgen: príkaz nenájdený
s9advgen: příkaz nenalezen
s9advgen: команда не найдена
s9advgen: командата не е открита
s9advgen: 命令找不到
s9advgen: コマンドが見つかりません