checkndx: 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/checkndx - from package: xbase-utils

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

On Debian possible default full paths are:

/usr/bin/checkndx - from package: libxbase64-bin

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

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