gnome-about: 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/gnome-about - from package: gnome-desktop

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

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