slrn: 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/slrn - from package: slrn

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

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