indexmaker: 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/indexmaker - from package: mrtg

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

On Debian possible default full paths are:

/usr/bin/indexmaker - from package: mrtg

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

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