omping: 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/omping - from package: omping

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

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