ht2html: 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/ht2html - from package: ht2html

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

Error in other languages:
ht2html: bevel nie gevind nie
ht2html: comandă negăsită
ht2html: comando não encontrado
ht2html: commande introuvable
ht2html: command not found
ht2html: käsku ei ole
ht2html: không tìm thấy lệnh
ht2html: komanda nerasta
ht2html: Kommando nicht gefunden.
ht2html: kommandot finns inte
ht2html: komut yok
ht2html: nie znaleziono polecenia
ht2html: níor aimsíodh an t-ordú
ht2html: no se encontró la orden
ht2html: no s'ha trobat l'ordre
ht2html: opdracht niet gevonden
ht2html: parancs nem található
ht2html: perintah tidak ditemukan
ht2html: príkaz nenájdený
ht2html: příkaz nenalezen
ht2html: команда не найдена
ht2html: командата не е открита
ht2html: 命令找不到
ht2html: コマンドが見つかりません