ipython: 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/ipython - from package: python-ipython-console

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

On Debian possible default full paths are:

/usr/bin/ipython - from package: ipython

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

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