hackrf_rffc5071: 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/hackrf_rffc5071 - from package: hackrf

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

Error in other languages:
hackrf_rffc5071: bevel nie gevind nie
hackrf_rffc5071: comandă negăsită
hackrf_rffc5071: comando não encontrado
hackrf_rffc5071: commande introuvable
hackrf_rffc5071: command not found
hackrf_rffc5071: käsku ei ole
hackrf_rffc5071: không tìm thấy lệnh
hackrf_rffc5071: komanda nerasta
hackrf_rffc5071: Kommando nicht gefunden.
hackrf_rffc5071: kommandot finns inte
hackrf_rffc5071: komut yok
hackrf_rffc5071: nie znaleziono polecenia
hackrf_rffc5071: níor aimsíodh an t-ordú
hackrf_rffc5071: no se encontró la orden
hackrf_rffc5071: no s'ha trobat l'ordre
hackrf_rffc5071: opdracht niet gevonden
hackrf_rffc5071: parancs nem található
hackrf_rffc5071: perintah tidak ditemukan
hackrf_rffc5071: príkaz nenájdený
hackrf_rffc5071: příkaz nenalezen
hackrf_rffc5071: команда не найдена
hackrf_rffc5071: командата не е открита
hackrf_rffc5071: 命令找不到
hackrf_rffc5071: コマンドが見つかりません