gak: 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/sbin/gak - from package: gui-apt-key

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

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