combineMUMs: 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/combineMUMs - from package: mummer

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

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