aunpack: 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/aunpack - from package: atool

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

On Debian possible default full paths are:

/usr/bin/aunpack - from package: atool

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

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