slon_watchdog: 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/bin/slon_watchdog - from package: slony1-2-bin

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

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