repo_manager: 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/repo_manager - from package: repo_manager

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

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