linuxdoc: 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/linuxdoc - from package: linuxdoc-tools

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

On Debian possible default full paths are:

/usr/bin/linuxdoc - from package: linuxdoc-tools

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

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