xymonnet: 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/lib/xymon/server/bin/xymonnet - from package: xymon

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

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