obrigado renato, as configuraçoes do source estao padrao, eu so adicionei um endereço invalido mas ja retirei usando o comando postado, apos retirar o synaptic voltou a funcionar normalmente.
sudo gedit /etc/apt/sources.list
# deb cdrom:[Ubuntu 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted
# See
http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
## Major bug fix updates produced after the final release of the
## distribution.
deb
http://br.archive.ubuntu.com/ubuntu/ gutsy-updates main restricted universe multiverse
deb-src
http://br.archive.ubuntu.com/ubuntu/ gutsy-updates main restricted universe multiverse #Added by software-properties
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb
http://br.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse
deb-src
http://br.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse #Added by software-properties
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
deb
http://archive.canonical.com/ubuntu gutsy partner
deb-src
http://archive.canonical.com/ubuntu gutsy partner
deb
http://security.ubuntu.com/ubuntu gutsy-security main restricted universe multiverse
deb-src
http://security.ubuntu.com/ubuntu gutsy-security main restricted universe multiverse #Added by software-properties
deb
http://br.archive.ubuntu.com/ubuntu/ gutsy-proposed restricted main universe multiverse
deb-src
http://br.archive.ubuntu.com/ubuntu/ gutsy-proposed restricted main universe multiverse #Added by software-properties
deb
http://archive.ubuntu.com/ubuntu/ gutsy main universe restricted multiverse
deb-src
http://archive.ubuntu.com/ubuntu/ gutsy universe main multiverse restricted #Added by software-properties
# deb cdrom:[APTonCD for ubuntu gutsy - i386 (2009-03-12 17:18) CD1]/ /
grato