r2: 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/r2 - from package: radare2

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

Error in other languages:
r2: bevel nie gevind nie
r2: comandă negăsită
r2: comando não encontrado
r2: commande introuvable
r2: command not found
r2: käsku ei ole
r2: không tìm thấy lệnh
r2: komanda nerasta
r2: Kommando nicht gefunden.
r2: kommandot finns inte
r2: komut yok
r2: nie znaleziono polecenia
r2: níor aimsíodh an t-ordú
r2: no se encontró la orden
r2: no s'ha trobat l'ordre
r2: opdracht niet gevonden
r2: parancs nem található
r2: perintah tidak ditemukan
r2: príkaz nenájdený
r2: příkaz nenalezen
r2: команда не найдена
r2: командата не е открита
r2: 命令找不到
r2: コマンドが見つかりません