htlatex: 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/htlatex - from package: tetex-tex4ht

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

On Debian possible default full paths are:

/usr/bin/htlatex - from package: tex4ht

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

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