ntpdate: 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/ntpdate - from package: ntpdate

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

On Debian possible default full paths are:

/usr/sbin/ntpdate - from package: ntpdate

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

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