man3: 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/man3 - from package: filesystem

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

Error in other languages:
man3: bevel nie gevind nie
man3: comandă negăsită
man3: comando não encontrado
man3: commande introuvable
man3: command not found
man3: käsku ei ole
man3: không tìm thấy lệnh
man3: komanda nerasta
man3: Kommando nicht gefunden.
man3: kommandot finns inte
man3: komut yok
man3: nie znaleziono polecenia
man3: níor aimsíodh an t-ordú
man3: no se encontró la orden
man3: no s'ha trobat l'ordre
man3: opdracht niet gevonden
man3: parancs nem található
man3: perintah tidak ditemukan
man3: príkaz nenájdený
man3: příkaz nenalezen
man3: команда не найдена
man3: командата не е открита
man3: 命令找不到
man3: コマンドが見つかりません