xfminvert: 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/xfminvert - from package: minc-tools

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

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