slon: command not found

Have You tried accessing the binary with the full path?

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 - from package: slony1-2-bin

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