slon_kill: 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_kill - from package: slony1-2-bin

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

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