Notes on Debian package (dpkg) regarding system cleanups

When working with Debian1 or Ubuntu2 systems, you will get in contact with Debians package manager apt (Advances packaging tool)3. But apt itself is only a frontend of dpkg making available higher-level functions such as autoremove or update. While being the tool of choice for installing packages, apt tends to be rather restrictive if you want to cleanup your system, e.g., after you’ve tested a package temporarily. So here are some things you can do in that case with dpkg and dpkg-query.

List, remove and purge installed packages

Using dpkg-query it is very easy to list all packages currently (semi-) installed on your system. Using --showformat we’re able to control the information displayed effectively removing table headers and descriptions used by dpkg-query by default.

basti@home:~$ dpkg-query --show --showformat='${db:Status-Abbrev} ${binary:Package} ${Version}\n'
ii  a11y-profile-manager-indicator 0.1.10-0ubuntu3
ii  account-plugin-facebook 0.12+16.04.20160126-0ubuntu1
ii  account-plugin-flickr 0.12+16.04.20160126-0ubuntu1
ii  account-plugin-google 0.12+16.04.20160126-0ubuntu1
ii  accountsservice 0.6.40-2ubuntu11.3
rc  accountwizard 4:15.12.3-0ubuntu1
ii  acl 2.2.52-3
ii  acpi-support 0.142
ii  acpid 1:2.0.26-1ubuntu2
ii  activity-log-manager 0.9.7-0ubuntu23

Notice the first entry on each line. While many combinations are possible4, generally you will come across ii for installed packages, rc for packages that have been removed, but some (configuration) files remained and un for fully uninstalled packages. Even if you only use apt, consider the --purge option for apt autoclean and apt remove because most of the time you want to remove the package binaries and all configuration files when deleting it. Default is to remove the package binaries only. That’s nice if you reinstall the package later, but maybe not what you want.

Building up on that, numerous cleanups are possible. So let’s create an alias and have a look.

basti@home:~$ alias dql="dpkg-query --show --showformat='\${db:Status-Abbrev} \${binary:Package} \${Version}\n'"

Count installed packages

basti@home:~$ dql | grep -e "^ii" | wc -l

List all packages matching a pattern

basti@home:~$ dql *xfce4*
un  xfce4
un  xfce4-power-manager

Purge all semi-installed packages

To remove all packages, that had been removed but not purged yet, combine the upper command with some basic linux pipes:

basti@home:~$ dql | grep -e "^rc" | awk '{print $2}' | sudo xargs dpkg -P

Remove everything matching a pattern

Be careful. This is highly automated. Make sure you set the right pattern.

basti@home:~$ dql *php*mysql* | grep -v -e "^un" | awk '{print $2}' | xargs sudo dpkg -P

Show all files related to a packages

Often you want to know, where a package was installed and what files are package-relevant. That’s a dpkg-query no-brainer.

basti@home:~$ dpkg-query -L account-plugin-facebook

Working with the log

As most linux tools, dpkg writes a log to /var/log/dpkg.log that can be utilized to gather some valuable information for system cleaup. For example you could list the timestamps and names of all package installations.

basti@home:~$ awk '$3~/^install$/ {print $1" "$2" "$4;}' /var/log/dpkg.log
2017-02-27 18:09:36 libevent-core-2.0-5:amd64
2017-02-27 18:09:36 mysql-server-5.7:amd64
2017-02-27 18:09:37 libhtml-template-perl:all
2017-02-27 18:09:37 mysql-server:all
2017-02-27 19:24:43 nano:amd64

This output can be piped through date parsing to find out, e.g., what packages had been installed within the last hour.

basti@home:~$ look_back_minutes=60; oldest=$( echo "$( date +%s ) - 60 * $look_back_minutes" | bc ); awk '$3~/^install$/ {print $1" "$2" "$4;}' /var/log/dpkg.log | tac | while read line; do ts=$( date --date="$( awk '{ print $1" "$2 }' <<< $line )" +%s); [ $ts -ge $oldest ] && echo $line || break; done

2017-02-27 19:24:43 nano:amd64

The code reads the log file reversed (tac) and breaks when the first entry was found, that does not suite the timing condition anymore. Disclaimer: The code above is pretty slow, so I’d be happily accept advice on optimization.

References and further reading