webhttrack: 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/webhttrack - from package: httrack

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

On Debian possible default full paths are:

/usr/bin/webhttrack - from package: webhttrack

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

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