Securing Your Web Server - Keeping Up to Date
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Now that the server is locked down with a minimal set of accounts and services, it is important to patch everything to make sure that everything is up-to-date. There are several update managers for Linux; the Advanced Packaging Tool (APT) comes with Ubuntu.
Keeping up-to-date is critical to the security of a web server. It used to be that there was a lag of months (30–120 days) between when vulnerability was discovered and seeing it successfully exploited on a system. Today, that time has been reduced to hours instead of days.
APT
The sources for APT reside in its configuration file /etc/apt/sources.list. You can edit this file to include other repositories on the Internet.
To update the system, basically, it’s as simple as:
apt-get update
Ign cdrom://Ubuntu-Server 6.10 _Edgy Eft_ - Release i386 (20061025.1) edgy/main
Translation-en_US
Ign cdrom://Ubuntu-Server 6.10 _Edgy Eft_ -Release i386 (20061025.1) edgy/restricted
Translation-en_US
Get:1 http://us.archive.ubuntu.com edgy Release.gpg [191B]
Ign http://us.archive.ubuntu.com edgy/main Translation-en_US
Get:2 http://security.ubuntu.com edgy-security Release.gpg [191B]
Ign http://security.ubuntu.com edgy-security/main Translation-en_US
Ign http://us.archive.ubuntu.com edgy/restricted Translation-en_US
Ign http://security.ubuntu.com edgy-security/restricted Translation-en_US
Hit http://security.ubuntu.com edgy-security Release
Get:3 http://us.archive.ubuntu.com edgy-updates Release.gpg [191B ]
Ign http://us.archive.ubuntu.com edgy-updates/main Translation-en_US
Ign http://us.archive.ubuntu.com edgy-updates/restricted Translation-en_US
Get:4 http://us.archive.ubuntu.com edgy-backports Release.gpg [191B]
Ign http://us.archive.ubuntu.com edgy-backports/main Translation-en_US
Ign http://us.archive.ubuntu.com edgy-backports/restricted Translation-en_US
Hit http://us.archive.ubuntu.com edgy Release
Hit http://security.ubuntu.com edgy-security/main Packages
Get:5 http://us.archive.ubuntu.com edgy-updates Release [23.3kB]
Hit http://security.ubuntu.com edgy-security/restricted Packages
Hit http://security.ubuntu.com edgy-security/main Sources
Hit http://security.ubuntu.com edgy-security/restricted Sources
Hit http://us.archive.ubuntu.com edgy-backports Release
Hit http://us.archive.ubuntu.com edgy/main Packages
Hit http://us.archive.ubuntu.com edgy/restricted Packages
Hit http://us.archive.ubuntu.com edgy/main Sources
Hit http://us.archive.ubuntu.com edgy/restricted Sources
Get:6 http://us.archive.ubuntu.com edgy-updates/main Packages [53.8kB]
Get:7 http://us.archive.ubuntu.com edgy-updates/restricted Packages [14B]
Get:8 http://us.archive.ubuntu.com edgy-updates/main Sources [16.3kB]
Get:9 http://us.archive.ubuntu.com edgy-updates/restricted Sources [14B]
Hit http://us.archive.ubuntu.com edgy-backports/main Packages
Hit http://us.archive.ubuntu.com edgy-backports/restricted Packages
Hit http://us.archive.ubuntu.com edgy-backports/main Sources
Hit http://us.archive.ubuntu.com edgy-backports/restricted Sources
Fetched 93.6kB in 9s (9939B/s)
Reading package lists... Done
APT keeps an inventory of what you have installed and cross-checks it against a cen tral repository on the Internet. If there is an update for a package, AP automatically goes out to the Internet and downloads it. Then you can control when the updates get applied using the Upgrade option.
After APT has retrieved any updates for your installed packages, you can apply the updates with:
apt-get upgrade
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter four of Securing Ajax Applications: Ensuring the Safety of the Dynamic Web, written by Christopher Wells (O'Reilly, 2007; ISBN: 0596529317). Check it out today at your favorite bookstore. Buy this book now.
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