oggconvert: 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/oggconvert - from package: oggconvert

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

On Debian possible default full paths are:

/usr/bin/oggconvert - from package: oggconvert

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

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