gqrx: command not found

Have You tried accessing the binary with the full path?

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/gqrx - from package: gqrx-sdr

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