====== Commandline ======

===== purge uninstalled kernels =====

<code bash>
dpkg -l | grep '^rc' | awk '{print $2}' | grep 'linux-image' | xargs sudo dpkg --purge
</code>

===== Disable fsync =====

This trick helps on BTRFS FS
<code bash>
apt-get install eatmydata
eatmydata apt-get update
</code>

Or wrap some commands permanently with eatmydata
<code bash>
ln -s /usr/bin/eatmydata /usr/local/bin/aptitude
ln -s /usr/bin/eatmydata /usr/local/bin/apt-get
ln -s /usr/bin/eatmydata /usr/local/bin/apt-cache
</code>

===== Playing with apt keys =====

<code bash>
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 8B48AD6246925553
</code>

<code bash>
sudo apt-get install debian-archive-keyring
wget http://ftp.pl.debian.org/debian/pool/main/p/pkg-mozilla-archive-keyring/pkg-mozilla-archive-keyring_1.1_all.deb
sudo dpkg -i pkg-mozilla-archive-keyring_1.1_all.deb
sudo apt-get update
</code>

<code bash>
gpg --keyserver pgpkeys.mit.edu --recv-key  8B48AD6246925553      
gpg -a --export 8B48AD6246925553 | sudo apt-key add -
</code>

<code bash>
apt-get update 2> /tmp/keymissing; for key in $(grep "NO_PUBKEY" /tmp/keymissing |sed "s/.*NO_PUBKEY //"); do echo -e "\nProcessing key: $key"; gpg --keyserver keyserver.ubuntu.com --recv $key && sudo gpg --export --armor $key | apt-key add -; done
</code>
===== List all package versions =====

<code bash>apt-cache policy lxc</code>
<code>
lxc:
  Installed: 1:1.0.6-6+deb8u2
  Candidate: 1:1.1.5-1
  Version table:
     1:1.1.5-1 0
        500 http://ftp.pl.debian.org/debian/ stretch/main amd64 Packages
 *** 1:1.0.6-6+deb8u2 0
        100 /var/lib/dpkg/status

</code>

===== Install specified version =====
<code>
apt-get install backupninja=0.9.8.1-1
apt-mark hold backupninja
</code>

===== Install with low prio questions =====
To change dpkg-configure question priorities:
<code bash>DEBIAN_PRIORITY=low apt-get install ...</code>

===== Install from backports =====
List version and priorities:
<code>apt-cache policy pulseaudio</code>
<code>apt-get install -t jessie-backports pulseaudio</code>
<code>aptitude -t jessie-backports</code>

<file | /etc/apt/preferences.d/backports>
Package: *
Pin: release a=jessie-backports
Pin-Priority: 500

Package: *
Pin: release a=stretch-backports
Pin-Priority: 500
</file>

===== Hold package =====
<code bash>echo package_name hold | sudo dpkg --set-selections</code>