pip2.6: 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/pip2.6 - from package: python-pip

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

Error in other languages:
pip2.6: bevel nie gevind nie
pip2.6: comandă negăsită
pip2.6: comando não encontrado
pip2.6: commande introuvable
pip2.6: command not found
pip2.6: käsku ei ole
pip2.6: không tìm thấy lệnh
pip2.6: komanda nerasta
pip2.6: Kommando nicht gefunden.
pip2.6: kommandot finns inte
pip2.6: komut yok
pip2.6: nie znaleziono polecenia
pip2.6: níor aimsíodh an t-ordú
pip2.6: no se encontró la orden
pip2.6: no s'ha trobat l'ordre
pip2.6: opdracht niet gevonden
pip2.6: parancs nem található
pip2.6: perintah tidak ditemukan
pip2.6: príkaz nenájdený
pip2.6: příkaz nenalezen
pip2.6: команда не найдена
pip2.6: командата не е открита
pip2.6: 命令找不到
pip2.6: コマンドが見つかりません