gnutls-serv: 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 CentOS possible default full paths are:

/usr/bin/gnutls-serv - from package: gnutls-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/gnutls-serv - from package: gnutls-bin

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

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