prosody-migrator: 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/prosody-migrator - from package: prosody

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

On Debian possible default full paths are:

/usr/bin/prosody-migrator - from package: prosody

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

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