om: 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/bin/om - from package: omhacks

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

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