man5: 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/man5 - from package: filesystem

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

Error in other languages:
man5: bevel nie gevind nie
man5: comandă negăsită
man5: comando não encontrado
man5: commande introuvable
man5: command not found
man5: käsku ei ole
man5: không tìm thấy lệnh
man5: komanda nerasta
man5: Kommando nicht gefunden.
man5: kommandot finns inte
man5: komut yok
man5: nie znaleziono polecenia
man5: níor aimsíodh an t-ordú
man5: no se encontró la orden
man5: no s'ha trobat l'ordre
man5: opdracht niet gevonden
man5: parancs nem található
man5: perintah tidak ditemukan
man5: príkaz nenájdený
man5: příkaz nenalezen
man5: команда не найдена
man5: командата не е открита
man5: 命令找不到
man5: コマンドが見つかりません