prosody: 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
/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/prosody - from package: prosody

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

On Debian possible default full paths are:

/usr/bin/prosody - from package: prosody

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