Packages

Debian and derivatives

Much of why Debian is a strong Linux distribution comes from the core of Debian namely its package management. Everything in Debian - every application, every component _everything_ is built into a package, and then that package is installed onto your system (either by the Installer, or by you).

There are over 29 thousand software packages available for Debian - everything from the Linux kernel to games.

And Apt is simply awesome! Learn more at https://wiki.debian.org/Apt or https://help.ubuntu.com/14.04/serverguide/package-management.html

Search for a package

Sometimes you're searching for a list of packages available. You can easily take care of that with apt-cache search.

What files did this package install?

The synaptic gui will have a 'properties' tab that lists all the files installed. On the console, you can use dpkg-query --listfiles package_name. I don't use apt-file since dpkg is already installed on a base system.

What package provides file Y?

dpkg-query --search z.so reveals the packages you could install that would possibly install the missing source file your linker is looking for.

You can also use the web interface at http://packages.ubuntu.com/

Remove old kernels

Kernels take up a lot of disk space. And once you've got a new one, the old ones really don't serve a purpose. autoremove is supposed to remove old kernels (keeping the currently running kernel plus the prior one or two for backups).

sudo apt-get autoremove

But sometimes old kernels are left lying around. Maybe a lot of them. I'm not sure why, because normally you would only be left with 2 or 3 kernels if you run autoremove (perhaps this is because you have old virtualboxes?).

The post-install script /etc/kernel/postinst.d/apt-auto-removal is responsible for keeping track of what to preserve. And it writes a manifest to /etc/apt/apt.conf.d/01autoremove-kernels.

# run the post-install script
sudo /etc/kernel/postinst.d/apt-auto-removal
# see what's reserved
cat /etc/apt/apt.conf.d/01autoremove-kernels

Let's use dpkg to see all the kernels that are currently installed. Note: there are other related packages like headers (linux-headers-*), but those are dependencies of the kernel images, and will be removed when we remove the images so we don't need to even look at them.

# the last pipe uses a simple extended grep to take the meta package 'linux-image-generic' out of our list
dpkg -l linux-image* | awk '/^ii/ { print $2 }' | grep -e [0-9]
# more complete perl-compatible regex to highlight the kernel release number
dpkg -l linux-image* | awk '/^ii/ { print $2 }' | grep -P '[0-9]+\.[0-9]+\.[0-9\-]+[0-9]+'

Manually compose an apt-get purge invocation of the kernels you don't want (keep the running kernel and the prior as a fallback).

sudo apt-get -y purge linux-image-3.13.0-44-generic linux-image-3.13.0-46-generic linux-image-3.13.0-48-generic linux-image-3.13.0-55-generic linux-image-3.13.0-71-generic linux-image-3.13.0-74-generic

RedHat and derivatives

There is Yum package manager for RedHat and derivatives.