hostap_diag: 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/sbin/hostap_diag - from package: hostap-utils

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

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