viewvc-mp.pyo: 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/lib/python2.6/site-packages/viewvc/bin/mod_python/viewvc-mp.pyo - from package: viewvc

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

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