occ: 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 Debian possible default full paths are:

/usr/sbin/occ - from package: owncloud

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

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