xymonclient-linux.sh: 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

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/xymonclient-linux.sh - from package: xymon-client

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