turnserver: 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

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/turnserver - from package: coturn
/usr/bin/turnserver - from package: rfc5766-turn-server
/usr/sbin/turnserver - from package: turnserver

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