xymoncfg: command not found

Have You tried accessing the binary with the full path?

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/client/bin/xymoncfg - from package: xymon-client
/usr/lib/xymon/server/bin/xymoncfg - from package: xymon

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