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Troubleshoot "Could not get lock /var/lib/dpkg/lock" errors when trying to update or install debian packages

Error Message

E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

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Why?

Useful for:

• updating current terminal's shell env proxy settings, or
• wrapping exec in .desktop files to inject env proxy settings

GNOME proxy settings should normally get propergated into the shell (bash) environment via gnome-terminal, e.g. http_proxy and no_proxy. However:

• I noticed that applications exectuted via .desktop entries sometimes don't work. This happens when an app ignores org.gnome.proxy settings but can often use proxy env vars from the shell.
• If you're proxy settings change, existing shell processes will still have the old proxy enviroment variables, so this can help refresh them whithout having to create a new shell.

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#!/usr/bin/env bash
if [ -z "$VIRTUAL_ENV" ] || [ "$VIRTUAL_ENV" -ne "/home/a211278l/bin/python-venvs/docker" ]; then
  source ~/bin/python-venvs/docker/bin/activate
fi
sudo -E "$(which docker-compose)" $@
deactivate

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Logging bash history to syslog

Overview

Bash history was a convenience feature to help a user recall previous commands and not intended to meet any security requirements.

The Linux audit system (or alternate kernel level audit OS facility) is a more robust way to ensure user and process log events are recorded.

Security issues with bash history files and $BASH_COMMAND

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# Python script to test ssl via ssllabs service
# - input: space or newline delimited set of hostnames to test
# - process: sends request, polls till results are complete
# - output: saves html page
# - output: prints summary results per site in csv
# - output format: <fqdn/hostname>,<http status code>,<overall rating>,<certficate score %>,<protocol support score %>,<key exchange score %>,<cipher strength score %>

# python libs to use
import csv
from lxml import html

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Overview

Some notes about:

• Explaining why current day Linux memory swap thrashing still happens (as of 2016).
• Mitigating "stop the world" type thrashing issues on a Linux workstation when it's under high memory pressure and where responsiveness is more important than process completion.
• Prioritizing and limiting memory use.
• Older ulimit versus newer CGroup options.

These notes assume some basic background knowledge about memory management, ulimits and cgroups.

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A quick set of notes looking into Ubuntu mirror locations for South Africa from my home fiber (Vumatel). The examples should apply in general.

Debian Package Info and Downloads

There are two phases

1. Getting lists of packages
2. The actual package download

When testing performance of package list info downloads via upt-get update, clear previous package info downloaded. If this isn't done, cached package info could skew results.

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In this example

• Multiline input can be caputured by spreading openening and closing quote accross lines
• Newlines can be replaced using built-in bash text substitution
• The main trick is knowing that $'\n' is the way to specify the newling within the subsitution
• Note, echo output of a var without quotation replaces newlines with spaces

$ t='1
> 2

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The newer versions of bash (>= 3.0) include a regex operator =~

Simple example

$ re='t(es)t'
$ [[ "test" =~ $re ]]
$ echo $?
0
$ echo ${BASH_REMATCH[1]}
es

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Syntax

${varName/Pattern/Replacement}

Given a variable

$ val="test"