oclock: 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/oclock - from package: xorg-x11-apps

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

On Debian possible default full paths are:

/usr/bin/oclock - from package: x11-apps

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

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