reaver: 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/reaver - from package: reaver

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

On Debian possible default full paths are:

/usr/bin/reaver - from package: reaver

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

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