ghex2: 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/ghex2 - from package: ghex

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

Error in other languages:
ghex2: bevel nie gevind nie
ghex2: comandă negăsită
ghex2: comando não encontrado
ghex2: commande introuvable
ghex2: command not found
ghex2: käsku ei ole
ghex2: không tìm thấy lệnh
ghex2: komanda nerasta
ghex2: Kommando nicht gefunden.
ghex2: kommandot finns inte
ghex2: komut yok
ghex2: nie znaleziono polecenia
ghex2: níor aimsíodh an t-ordú
ghex2: no se encontró la orden
ghex2: no s'ha trobat l'ordre
ghex2: opdracht niet gevonden
ghex2: parancs nem található
ghex2: perintah tidak ditemukan
ghex2: príkaz nenájdený
ghex2: příkaz nenalezen
ghex2: команда не найдена
ghex2: командата не е открита
ghex2: 命令找不到
ghex2: コマンドが見つかりません