db2x_manxml: 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/db2x_manxml - from package: docbook2X

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

On Debian possible default full paths are:

/usr/bin/db2x_manxml - from package: docbook2X

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

Error in other languages:
db2x_manxml: bevel nie gevind nie
db2x_manxml: comandă negăsită
db2x_manxml: comando não encontrado
db2x_manxml: commande introuvable
db2x_manxml: command not found
db2x_manxml: käsku ei ole
db2x_manxml: không tìm thấy lệnh
db2x_manxml: komanda nerasta
db2x_manxml: Kommando nicht gefunden.
db2x_manxml: kommandot finns inte
db2x_manxml: komut yok
db2x_manxml: nie znaleziono polecenia
db2x_manxml: níor aimsíodh an t-ordú
db2x_manxml: no se encontró la orden
db2x_manxml: no s'ha trobat l'ordre
db2x_manxml: opdracht niet gevonden
db2x_manxml: parancs nem található
db2x_manxml: perintah tidak ditemukan
db2x_manxml: príkaz nenájdený
db2x_manxml: příkaz nenalezen
db2x_manxml: команда не найдена
db2x_manxml: командата не е открита
db2x_manxml: 命令找不到
db2x_manxml: コマンドが見つかりません