happy: 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/happy - from package: happy

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

On Debian possible default full paths are:

/usr/bin/happy - from package: happy

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

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