man7: 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/man7 - from package: filesystem

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

Error in other languages:
man7: bevel nie gevind nie
man7: comandă negăsită
man7: comando não encontrado
man7: commande introuvable
man7: command not found
man7: käsku ei ole
man7: không tìm thấy lệnh
man7: komanda nerasta
man7: Kommando nicht gefunden.
man7: kommandot finns inte
man7: komut yok
man7: nie znaleziono polecenia
man7: níor aimsíodh an t-ordú
man7: no se encontró la orden
man7: no s'ha trobat l'ordre
man7: opdracht niet gevonden
man7: parancs nem található
man7: perintah tidak ditemukan
man7: príkaz nenájdený
man7: příkaz nenalezen
man7: команда не найдена
man7: командата не е открита
man7: 命令找不到
man7: コマンドが見つかりません