discard: 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/discard - 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/discard - from package: mailman

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

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