osmocom_fft: 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/osmocom_fft - from package: gr-osmosdr

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

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