mmls: 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/mmls - from package: sleuthkit

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

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