nightfall: 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 CentOS possible default full paths are:

/usr/bin/nightfall - from package: nightfall

You may install the required package with command yum install {package}

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