uwsgi_lua51: 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 Debian possible default full paths are:

/usr/bin/uwsgi_lua51 - from package: uwsgi-plugin-lua5.1

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

Error in other languages:
uwsgi_lua51: bevel nie gevind nie
uwsgi_lua51: comandă negăsită
uwsgi_lua51: comando não encontrado
uwsgi_lua51: commande introuvable
uwsgi_lua51: command not found
uwsgi_lua51: käsku ei ole
uwsgi_lua51: không tìm thấy lệnh
uwsgi_lua51: komanda nerasta
uwsgi_lua51: Kommando nicht gefunden.
uwsgi_lua51: kommandot finns inte
uwsgi_lua51: komut yok
uwsgi_lua51: nie znaleziono polecenia
uwsgi_lua51: níor aimsíodh an t-ordú
uwsgi_lua51: no se encontró la orden
uwsgi_lua51: no s'ha trobat l'ordre
uwsgi_lua51: opdracht niet gevonden
uwsgi_lua51: parancs nem található
uwsgi_lua51: perintah tidak ditemukan
uwsgi_lua51: príkaz nenájdený
uwsgi_lua51: příkaz nenalezen
uwsgi_lua51: команда не найдена
uwsgi_lua51: командата не е открита
uwsgi_lua51: 命令找不到
uwsgi_lua51: コマンドが見つかりません