check_db: 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/lib/mailman/bin/check_db - from package: mailman

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

On Debian possible default full paths are:

/usr/lib/mailman/bin/check_db - from package: mailman
/usr/sbin/check_db - from package: mailman

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

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