oping: 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/oping - from package: liboping

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

On Debian possible default full paths are:

/usr/bin/oping - from package: oping

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

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