pxe-kexec: 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/sbin/pxe-kexec - from package: pxe-kexec

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