mod_python: 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 - from package: viewvc

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

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