htdb_stat: 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_stat - from package: htdig

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

On Debian possible default full paths are:

/usr/bin/htdb_stat - from package: htdig

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

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