ratpoison: 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/ratpoison - from package: ratpoison

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

On Debian possible default full paths are:

/usr/bin/ratpoison - from package: ratpoison

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

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