mirrorprobe: 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/mirrorprobe - from package: mirrorbrain-tools

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

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