gnac: 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/gnac - from package: gnac

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

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