nping: 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/nping - from package: nmap

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

On Debian possible default full paths are:

/usr/bin/nping - from package: nmap

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

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