sitesummary-update-nagios: 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/sbin/sitesummary-update-nagios - from package: sitesummary

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

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