dmidecode: 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:

/usr/sbin/dmidecode - from package: dmidecode

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

On Debian possible default full paths are:

/usr/sbin/dmidecode - from package: dmidecode

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

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