xautolock: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

/usr/bin/xautolock - from package: xautolock

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