nighthttpd: 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/sbin/nighthttpd - from package: nightview-server

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

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