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

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

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