dynamodb_dump: 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/dynamodb_dump - from package: python2-boto
/usr/bin/dynamodb_dump - from package: python-boto

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

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