mcfirst: 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/mcfirst - from package: ssmping

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

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