If you are downloading a package from untrusted or questionable sources, be paranoid. On popular forums like ubuntuforums.org, if a user makes his first post containing only of a short text like "install this, works for me!", followed by a link, be careful with that link and/ or instructions.
Don't use binary packages if possible, especially from untrusted sources. Get the source (for official Ubuntu packages, this can be done with
apt-get source package-name) and have a look at it.
If the package in question is small, it may be worth analysing it. I prefer to use the terminal for that because I then have fast access to other powerful command-line tools like
dpkg and lots others. Make use of tab-completion (i.e. hitting Tab to complete commands and filenames), it really saves time!
To download a .deb file, you can use the browser, but copying the link and then use
wget is faster since you can already experiment with it.
$ mkdir /tmp/foo && cd /tmp/foo
$ wget http://nl.archive.ubuntu.com/ubuntu/pool/main/n/nvidia-common/nvidia-common_0.2.35_amd64.deb
Next, it's time to check the file itself.
lesspipe) can provide a quick overview of the file contents. Arrow keys, page up/down, home/end can be useful for navigating, Q quits the program.
$ less nvidia-common_0.2.35_amd64.deb
new debian package, version 2.0.
size 10802 bytes: control archive= 1877 bytes.
197 bytes, 11 lines * config #!/bin/sh
703 bytes, 16 lines control
741 bytes, 10 lines md5sums
163 bytes, 9 lines * postinst #!/bin/sh
206 bytes, 8 lines * postrm #!/bin/sh
827 bytes, 38 lines * preinst #!/bin/sh
263 bytes, 14 lines * prerm #!/bin/sh
365 bytes, 12 lines templates
Maintainer: Ubuntu Developers <email@example.com>
Pre-Depends: dpkg (>= 22.214.171.124)
Depends: python2.7 | python2.6, python (>= 2.7.1-0ubuntu2), python (<< 2.8), debconf (>= 0.5.00) | debconf-2.0, pciutils, python-apt
Conflicts: nvidia-180-modaliases, nvidia-185-modaliases, nvidia-current-modaliases
Replaces: nvidia-180-modaliases, nvidia-185-modaliases, nvidia-current-modaliases
Description: Find obsolete NVIDIA drivers
This package will find obsolete NVIDIA drivers in use,
detect the hardware and recommend the most appropriate
Python-Version: 2.6, 2.7
drwxr-xr-x root/root 0 2011-09-07 11:06 ./
drwxr-xr-x root/root 0 2011-09-07 11:06 ./usr/
drwxr-xr-x root/root 0 2011-09-07 11:06 ./usr/share/
drwxr-xr-x root/root 0 2011-09-07 11:06 ./usr/share/doc/
drwxr-xr-x root/root 0 2011-09-07 11:06 ./usr/share/doc/nvidia-common/
-rw-r--r-- root/root 1174 2011-09-07 11:07 ./usr/share/doc/nvidia-common/changelog.gz
-rw-r--r-- root/root 466 2011-06-24 14:45 ./usr/share/doc/nvidia-common/copyright
After this, you get an overview of the package dependencies and what kind of files it possibly contains. Time to extract the files and analyse the contents using
dpkg-deb. The first command extracts the file tree in a newly created directory
fs, the second one extracts it to
DEBIAN because no other target is specified:
$ dpkg-deb -x nvidia-common_0.2.35_amd64.deb fs
$ dpkg-deb -e nvidia-common_0.2.35_amd64.deb
less again to analyze the contents of the maintainer scripts (i.e. the files that will be used/ run during installation (and removal).
postinst are scripts run before/after removal/installation which are the most important files to analyse. Use
:p to switch between the files. By pressing
=, you get the current file name and line number as well as the number of files that are in the list.
$ less DEBIAN/*
If the package scripts look sane, it's time to analyse the installed contents (use tab-completion). For shell scripts and interpreted scripts (like Python), analysis is easier (assuming that you're known with the language).
$ less fs/usr/bin/nvidia-detector # fs<TAB><TAB>/usr/ <TAB><TAB>bin ...
$ less fs/usr/lib/nvidia/pre-install
$ ls -la fs/usr/lib # quickly check the directory contents, my memory is weak
drwxr-xr-x 5 peter peter 100 2011-09-07 11:06 .
drwxr-xr-x 5 peter peter 100 2011-09-07 11:06 ..
drwxr-xr-x 2 peter peter 60 2011-09-07 11:06 nvidia
drwxr-xr-x 3 peter peter 60 2011-09-07 11:06 python2.6
drwxr-xr-x 3 peter peter 60 2011-09-07 11:06 python2.7
$ # I conclude: python2.6 is not a symlink to python2.7
$ less fs/usr/lib/python2.7/dist-packages/NvidiaDetector/*
press 'v' to open an editor (e.g. nano, vim) to get syntax highlighting if preferable
Pay special attention to configuration files, especially if they are using directories like
/etc/init (for startup scripts) or
/etc/modprobe.d (options for loading kernel modules).
ldd can give an idea what a program could be used for. The below program looks like a graphical program that uses OpenGL.
$ ldd /usr/bin/glxgears
linux-vdso.so.1 => (0x00007fff7d3ff000)
libGL.so.1 => /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1 (0x00007fa2ead11000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fa2eaa8d000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007fa2ea754000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fa2ea3b5000)
After you are sure that the package looks valid, you can go on install it in VirtualBox booting off a Live CD and use
strace -f -o logfile.txt programname for further analysis.