gtk-lshw: 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/sbin/gtk-lshw - from package: lshw-gui

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

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