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

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

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