isag: 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/isag - from package: isag

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

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