viewumount: 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/viewumount - from package: umview

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

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