half_mt: 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/bin/half_mt - from package: LibRaw-samples

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

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