unmass: 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/unmass - from package: unmass

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

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