sphinx-quickstart: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/sphinx-quickstart - from package: python-sphinx

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