ophelp: 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/ophelp - from package: oprofile

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

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