rainbow-xify: 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 Debian possible default full paths are:

/usr/bin/rainbow-xify - from package: rainbow

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

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