viewvc.cgi: 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/cgi/viewvc.cgi - from package: viewvc

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

On Debian possible default full paths are:

/usr/share/gforge/www/scm/viewvc/bin/cgi/viewvc.cgi - from package: gforge-web-apache2

You may install the required package with command apt-get install {package}

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