mandb: 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 Debian possible default full paths are:

/usr/bin/mandb - from package: man-db

You may install the required package with command apt-get install {package}

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