ping_pong: 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/ping_pong - from package: ctdb

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

On Debian possible default full paths are:

/usr/bin/ping_pong - from package: ctdb

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

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