yubikey-personalization-gui: 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/yubikey-personalization-gui - from package: yubikey-personalization-gui

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

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