docbook2tex: 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/docbook2tex - from package: docbook-utils

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

On Debian possible default full paths are:

/usr/bin/docbook2tex - from package: docbook-utils

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

Error in other languages:
docbook2tex: bevel nie gevind nie
docbook2tex: comandă negăsită
docbook2tex: comando não encontrado
docbook2tex: commande introuvable
docbook2tex: command not found
docbook2tex: käsku ei ole
docbook2tex: không tìm thấy lệnh
docbook2tex: komanda nerasta
docbook2tex: Kommando nicht gefunden.
docbook2tex: kommandot finns inte
docbook2tex: komut yok
docbook2tex: nie znaleziono polecenia
docbook2tex: níor aimsíodh an t-ordú
docbook2tex: no se encontró la orden
docbook2tex: no s'ha trobat l'ordre
docbook2tex: opdracht niet gevonden
docbook2tex: parancs nem található
docbook2tex: perintah tidak ditemukan
docbook2tex: príkaz nenájdený
docbook2tex: příkaz nenalezen
docbook2tex: команда не найдена
docbook2tex: командата не е открита
docbook2tex: 命令找不到
docbook2tex: コマンドが見つかりません