hackrf_info: 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_info - from package: hackrf

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

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