kexec: 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:

/sbin/kexec - from package: kexec-tools

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

On Debian possible default full paths are:

/sbin/kexec - from package: kexec-tools

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

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