uhd_rx_nogui: 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/uhd_rx_nogui - from package: gnuradio

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

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