sphinx-build: 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-build - from package: python-sphinx

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