muffin-theme-viewer: 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/muffin-theme-viewer - from package: muffin

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

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