hrepack: 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/hrepack - from package: hdf

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

On Debian possible default full paths are:

/usr/bin/hrepack - from package: hdf4-tools

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

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