turnutils_stunclient: 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/turnutils_stunclient - from package: coturn
/usr/bin/turnutils_stunclient - from package: rfc5766-turn-server

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

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