libgnutls-config: 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/libgnutls-config - from package: gnutls-devel

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

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