rman: 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/rman - from package: rman

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

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