update-xscreensaver-hacks: 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/update-xscreensaver-hacks - from package: xscreensaver-base

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

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