snapshot.cgi: 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/snapshot.cgi - from package: xymon

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

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