You should conduct security updates frequently. The vast majority of exploits result from known vulnerabilities that have not been patched in time, as this
http://www.cs.umd.edu/~waa/vulnerability.html (presented at the 2001 IEEE Symposium on Security and Privacy) explains. Updates are described under
第 4.2 节 “进行安全更新”.
Debian does have a specific tool to check if a system needs to be updated but many users will just want to manually check if any security updates are available for their system.
如果您如
第 4.2 节 “进行安全更新” 所述, 配置了系统. 那么, 仅需要:
# apt-get update
# apt-get upgrade -s
[ ... review packages to be upgraded ... ]
# apt-get upgrade
# checkrestart
[ ... restart services that need to be restarted ... ]
And restart those services whose libraries have been updated if any. Note: Read
第 4.2 节 “进行安全更新” for more information on library (and kernel) upgrades.
第一行将从您配置的源下载可用软件包列表. -s 将做一个模拟运行, 即并不真的下载, 并安装软件包, 而只是告诉您将会下载/安装哪些. 从输出中, 您可以知道 Debian 对哪些软件包做了修补, 可以做为一个安全更新. 例如:
# apt-get upgrade -s
Reading Package Lists... Done
Building Dependency Tree... Done
2 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Inst cvs (1.11.1p1debian-8.1 Debian-Security:3.0/stable)
Inst libcupsys2 (1.1.14-4.4 Debian-Security:3.0/stable)
Conf cvs (1.11.1p1debian-8.1 Debian-Security:3.0/stable)
Conf libcupsys2 (1.1.14-4.4 Debian-Security:3.0/stable)
Notice that you will need to reboot your system if there has been a kernel upgrade.
10.1.2.2. Checking for updates at the Desktop
Since Debian 4.0 lenny Debian provides and installs in a default installation update-notifier. This is a GNOME application that will startup when you enter your Desktop and can be used to keep track of updates available for your system and install them. It uses update-manager for this.
In a stable system updates are only available when a security patch is available or at point releases. Consequently, if the system is properly configured to receive security updates as described in
第 4.2 节 “进行安全更新” and you have a cron task running to update the package information you will be notified through an icon in the desktop notifcation area.
The notification is not intrusive and users are not forced to install updates. From the notification icon a desktop user (with the administrator's password) can access a simple GUI to show available updates and install them.
This application works by checking the package database and comparing the system with its contents. If the package database is updated periodically through a cron task then the contents of the database will be newer than the packages installed in the system and the application will notify you.
Apt installs such a task (/etc/cron.d/apt) which will run based on Apt's configuration (more specifically APT::Periodic). In the GNOME environment this configuration value can be adjusted by going to System > Admin > Software origins > Updates, or running /usr/bin/software-properties.
If the system is set to download the packages list daily but not download the packages themselves your
/etc/apt/apt.conf.d/10periodic should look like this:
APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Download-Upgradeable-Packages "0";
You can use a different cron task, such as the one installed by
cron-apt (see
第 10.1.2.3 节 “使用 cron-apt 自动完成更新检查”). You can also just manually check for upgrades using this application.
Users of the KDE desktop environment will probably prefer to install adept and adept-notifier instead which offers a similar functionality but is not part of the standard installation.
10.1.2.3. 使用 cron-apt 自动完成更新检查
Another method for automatic security updates is the use of cron-apt. This package provides a tool to update the system at regular intervals (using a cron job), and can also be configured to send mails to the system administrator using the local mail transport agent. It will just update the package list and download new packages by default but it can be configured to automatically install new updates.
Notice that you might want to check the distribution release, as described in
第 7.5.3 节 “Per distribution release check”, if you intend to automatically updated your system (even if only downloading the packages). Otherwise, you cannot be sure that the downloaded packages really come from a trusted source.
10.1.2.4. Automatically checking for security issues with debsecan
The
debsecan program evaluates the security status of by reporting both missing security updates and security vulnerabilities. Unlike
cron-apt, which only provides information related to security updates available, but this tool obtains information from the security vulnerability database maintained by the Debian Security Team which includes also information on vulnerabilities which are not yet fixed through a security update. Consequently, it is more efficient at helping administrators track security vulnerabilities (as described in
第 10.1.1 节 “Tracking security vulnerabilities”).
Upon installing the Debian package debsecan, and if the administrator consents to it, it will generate a cron task that will make it run and send the output to a specific user whenever it finds a vulnerable package. It will also download the information from the Internet. The location of the security database is also part of the questions ask on installation and are later defined /etc/default/debsecan, it can be easily adjusted for systems that do not have Internet access so that they all pull from a local mirror so that there is a single point that access the vulnerability database.
Notice, however, that the Security Team tracks many vulnerabilities including low-risk issues which might not be fixed through a security update and some vulnerabilities initially reported as affecting Debian might, later on, upon investigation, be dismissed. Debsecan will report on all the vulnerabilities, which makes it a quite more verbose than the other tools described above.
