ipdb: 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/ipdb - from package: python-ipdb

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

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