xscreensaver: 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/xscreensaver - from package: xscreensaver-base

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

On Debian possible default full paths are:

/usr/bin/xscreensaver - from package: xscreensaver

You may install the required package with command apt-get install {package}

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