se_synaptic: 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/se_synaptic - from package: policycoreutils

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

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