mixmaster-filter: 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/mixmaster-filter - from package: mixmaster

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

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