htdb_dump: 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/htdb_dump - from package: htdig

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

On Debian possible default full paths are:

/usr/bin/htdb_dump - from package: htdig

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

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