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

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

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