man3x: 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/man3x - from package: filesystem

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

Error in other languages:
man3x: bevel nie gevind nie
man3x: comandă negăsită
man3x: comando não encontrado
man3x: commande introuvable
man3x: command not found
man3x: käsku ei ole
man3x: không tìm thấy lệnh
man3x: komanda nerasta
man3x: Kommando nicht gefunden.
man3x: kommandot finns inte
man3x: komut yok
man3x: nie znaleziono polecenia
man3x: níor aimsíodh an t-ordú
man3x: no se encontró la orden
man3x: no s'ha trobat l'ordre
man3x: opdracht niet gevonden
man3x: parancs nem található
man3x: perintah tidak ditemukan
man3x: príkaz nenájdený
man3x: příkaz nenalezen
man3x: команда не найдена
man3x: командата не е открита
man3x: 命令找不到
man3x: コマンドが見つかりません