我在几台面向互联网的服务器上运行 ubuntu。
我最近发现我使用的官方 ubuntu 镜像严重过时；当我更改源并更新 apt 时，我惊讶地发现大约有 5 GB 的软件包已经过时并需要更新。这些软件包包括apt，linux-base以及我认为对我的系统安全至关重要的其他软件包。这让我很困惑，因为我以为安全更新是直接从 中获取的security.ubuntu.com。
因此，我想问以下问题：
Ubuntu 是否以某种方式依赖主镜像的“新鲜度”来确保其安全性？或者换句话说：过时的非镜像是否会以
security某种方式妨碍或破坏 Ubuntu 自我更新的能力？该
*-security存储库是否包含发行版生命周期内由规范发布的所有安全更新？
编辑2019-10-29：根据要求，以下是来自其中一台服务器的 sources.list。请注意，这是 ubuntu 附带的库存文件。唯一的变化是用 替换了过时镜像的 URL archive.ubuntu.com。我还擅自将问题的范围分成一组简单的是非问题，以限制问题的范围。
#
# deb cdrom:[Ubuntu-Server 18.04.2 LTS _Bionic Beaver_ - Release amd64 (20190210)]/ bionic main restricted
#deb cdrom:[Ubuntu-Server 18.04.2 LTS _Bionic Beaver_ - Release amd64 (20190210)]/ bionic main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu/ bionic main restricted
# deb-src http://archive.ubuntu.com/ubuntu/ bionic main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
# deb-src http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu/ bionic universe
# deb-src http://archive.ubuntu.com/ubuntu/ bionic universe
deb http://archive.ubuntu.com/ubuntu/ bionic-updates universe
# deb-src http://archive.ubuntu.com/ubuntu/ bionic-updates universe
## 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.
deb http://archive.ubuntu.com/ubuntu/ bionic multiverse
# deb-src http://archive.ubuntu.com/ubuntu/ bionic multiverse
deb http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse
# deb-src http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse
## 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://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
## 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 bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner
deb http://security.ubuntu.com/ubuntu bionic-security main restricted
# deb-src http://security.ubuntu.com/ubuntu bionic-security main restricted
deb http://security.ubuntu.com/ubuntu bionic-security universe
# deb-src http://security.ubuntu.com/ubuntu bionic-security universe
deb http://security.ubuntu.com/ubuntu bionic-security multiverse
# deb-src http://security.ubuntu.com/ubuntu bionic-security multiverse