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:

/bin/dmesg - from package: util-linux-ng

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

On Debian possible default full paths are:

/bin/dmesg - from package: util-linux
/usr/lib/klibc/bin/dmesg - from package: klibc-utils

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

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