unrar-free: 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/unrar-free - from package: unrar-free

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

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