efivar: command not found

Have You tried accessing the binary with the full path?

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/efivar - from package: efivar

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