viewvc.wsgi: 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/wsgi/viewvc.wsgi - from package: viewvc

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

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