vmcore-dmesg: 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/vmcore-dmesg - from package: kexec-tools

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

On Debian possible default full paths are:

/sbin/vmcore-dmesg - from package: kexec-tools

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

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