night_dark: 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/night_dark - from package: nightview-cli

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

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