db2html: 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/db2html - from package: docbook-utils

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

On Debian possible default full paths are:

/usr/bin/db2html - from package: docbook-utils

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

Error in other languages:
db2html: bevel nie gevind nie
db2html: comandă negăsită
db2html: comando não encontrado
db2html: commande introuvable
db2html: command not found
db2html: käsku ei ole
db2html: không tìm thấy lệnh
db2html: komanda nerasta
db2html: Kommando nicht gefunden.
db2html: kommandot finns inte
db2html: komut yok
db2html: nie znaleziono polecenia
db2html: níor aimsíodh an t-ordú
db2html: no se encontró la orden
db2html: no s'ha trobat l'ordre
db2html: opdracht niet gevonden
db2html: parancs nem található
db2html: perintah tidak ditemukan
db2html: príkaz nenájdený
db2html: příkaz nenalezen
db2html: команда не найдена
db2html: командата не е открита
db2html: 命令找不到
db2html: コマンドが見つかりません