in.ftpd: 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/sbin/in.ftpd - from package: ftpd-ssl
/usr/sbin/in.ftpd - from package: ftpd

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

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