first: 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/first - from package: yagiuda

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

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