authconfig-gtk: 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/authconfig-gtk - from package: authconfig-gtk
/usr/sbin/authconfig-gtk - from package: authconfig-gtk

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

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