man8x: 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/share/man/bin/man8x - from package: filesystem

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

Error in other languages:
man8x: bevel nie gevind nie
man8x: comandă negăsită
man8x: comando não encontrado
man8x: commande introuvable
man8x: command not found
man8x: käsku ei ole
man8x: không tìm thấy lệnh
man8x: komanda nerasta
man8x: Kommando nicht gefunden.
man8x: kommandot finns inte
man8x: komut yok
man8x: nie znaleziono polecenia
man8x: níor aimsíodh an t-ordú
man8x: no se encontró la orden
man8x: no s'ha trobat l'ordre
man8x: opdracht niet gevonden
man8x: parancs nem található
man8x: perintah tidak ditemukan
man8x: príkaz nenájdený
man8x: příkaz nenalezen
man8x: команда не найдена
man8x: командата не е открита
man8x: 命令找不到
man8x: コマンドが見つかりません