pip: 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/pip - from package: python-pip

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

On Debian possible default full paths are:

/usr/bin/pip - from package: python-pip

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

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