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Chris Lamb: find(1), trailing slashes and symbolic links to directories

Planet ALUG - Wed, 24/12/2014 - 23:06

Here's a nice little "gotcha" in find(1).

First, let's create a directory and a symlink to that directory. We'll add an empty file just underneath to illustrate what is going on:

$ mkdir a $ ln -s a b $ touch a/file

If we invoke find with a trailing slash, everything works as expected:

$ find a/ a/ a/file $ find b/ b/ b/file

... but if we omit the trailing slash, find does not traverse the symlink:

$ find a a a/file $ find b b

This implies that any normal-looking invokation of find such as:

find /path/to/dir -name 'somefile.ext' ...

... is subtly buggy as it won't accomodate the sysadmin replacing that path with a symlink.

This is, of course, well-covered in the find(1) manpage (spoiler: the safest option is to specify -H, or simply to append the trailing slash), but I would still class this as a "gotcha" because of the subtle difference between the trailing and non-trailing slash variants.

Putting it another way, it's completely reasonable that find doesn't follow symlinks, but when this behaviour based on the presence of the trailing slash—a usually meaningless syntactic distinction—it crosses the rubicon to being counter-intutive.

Categories: LUG Community Blogs

Chris Lamb: 8:20AM. Sunday, 22 December 2013

Planet ALUG - Wed, 24/12/2014 - 20:39

Running east into the sun, he hadn't seen another human for over half an hour. He navigates Westferry Circus and heads south, cutting from the road through to the riverside pathway. He keeps is breathing steady - no reason to hurry.

The wind catches him from Westminster. It smells slightly salty but it's an ersatz attempt, nowhere near bracing enough to be a real sea breeze.

Pressing on, the vacant citadel of Canary Wharf disappears behind him. But as the peninsula curves around, a man appears in the distance. Even half a mile away he looks out of place, or rather—given the hour—time. He's walking purposefully, but it doesn't feel the kind of route someone would be taking to work. He's not wearing quite enough clothes for the weather either, and homeless people are rarely made to feel welcome in the Docklands. His supermarket denim visibly flaps in the breeze. "Relaxed fit", they call it.

When he gets within earshot the man cocks his head, not expecting to hear the regular cadence of approaching footsteps. He turns slightly to reveal he's cradling a large bottle of Coca-Cola, meekly wrapped in the swathing bands of two anonymously blue corner-shop plastic bags.

The runner eyes the Coke greedily but can quickly see that it has already been opened, tainted. Although only a mouthful or so has gone, a brown froth sloshes against the top of the container. Amateur, he thinks. He'll regret that later.

He looks back up to the man, who is now smiling at him. His left hand bccomes visible as he strides: a four-pack of Carling. The man laughs.

"Oh, you and me mate are worlds apart!" the man shouts.

It's immediately friendly. He starts to raise his Carling as but thinks better of it. It's momentarily awkward.

"Worlds apart mate", the man continues. "Have a good one!"

The runner smiles back.

Only in time, the runner thinks. They both can't stop.

Categories: LUG Community Blogs

Mick Morgan: merry christmas 2014

Planet ALUG - Wed, 24/12/2014 - 18:26

As I have noted before, 24 December is trivia’s birthday. Since my first post dates from 24 December 2006, today is trivia’s eighth birthday. It seems like only yesterday.

I haven’t posted much in the last few months. I have a lot of material I need to cover, and a backlog of articles I want (or at least wanted) to write so I will endeavour to get back into a writing routine as soon as I can. Meanwhile, since it is yet again christmas time, and it’s trivia’s birthday, I couldn’t let today pass unblogged.

Let’s hope 2015 brings all that you wish for.

Best Wishes

Mick

Categories: LUG Community Blogs

Steve Kemp: Switched to using attic for backups

Planet HantsLUG - Fri, 19/12/2014 - 00:00

Even though seeing the word attic reminds me too much of leaking roofs and CVS, I've switched to using the attic backup tool.

I want a simple system which will take incremental backups, perform duplication-elimination (to avoid taking too much space), support encryption, and be fast.

I stopped using backup2l because the .tar.gz files were too annoying, and it was too slow. I started using obnam because I respect Lars and his exceptionally thorough testing-regime, but had to stop using it when things started getting "too slow".

I'll document the usage/installation in the future. For the moment the only annoyance is that it is contained in the Jessie archive, not the Wheezy one. Right now only 2/19 of my hosts are Jessie.

Categories: LUG Community Blogs

Mick Morgan: solidarity with the tor project

Planet ALUG - Sat, 13/12/2014 - 19:16

On Thursday 11 December, Roger Dingledine of the Tor project posted the following email to the “tor-talk” mail list (to which I am subscribed).

I’d like to draw your attention to

https://blog.torproject.org/blog/solidarity-against-online-harassment
https://twitter.com/torproject/status/543154161236586496

One of our colleagues has been the target of a sustained campaign of harassment for the past several months. We have decided to publish this statement to publicly declare our support for her, for every member of our organization, and for every member of our community who experiences this harassment. She is not alone and her experience has catalyzed us to action. This statement is a start.

Roger asked those who deplored on-line harassment (of any person, for any reason) and who supported the Tor project’s action in publicly condemning the harassment of one of the Tor developers to add their name and voice to the blog post.

I am proud to have done so.

Categories: LUG Community Blogs

Joint meeting hosted by Portsmouth, 20 Dec 2014

Surrey LUG - Thu, 11/12/2014 - 23:12
Start: 2014-12-20 13:00 End: 2014-12-20 18:00

The Portsmouth LUG have invited us to join them.

All of you are warmly invited to the Portsmouth LUG Bring a Box meeting, on Saturday, 20th December, from 13:00 to 18:00 at the Broadoaks Social Club.
http://www.broadoaksocialclub.net/where.html

The talk that had to be put off last month will take place this.  Keith Edmunds of Tiger Computing will talk to us about running an entirely Linux Consultancy.

Categories: LUG Community Blogs

Ben Francis: The Times They Are A Changin’ (Open Web Remix)

Planet ALUG - Thu, 11/12/2014 - 11:26

In the run up to the “Mozlandia” work week in Portland, and in reflection of the last three years of the Firefox OS project, for a bit of fun I’ve reworked a Bob Dylan song to celebrate our incredible journey so far.

Here’s a video featuring some of my memories from the last three years, with Siobhan (my fiancée) and me singing the song at you! There are even lyrics so you can sing along

“Keep on rockin’ the free web” — Potch

Categories: LUG Community Blogs

Steve Kemp: An anniversary and a retirement

Planet HantsLUG - Thu, 11/12/2014 - 10:56

On this day last year I we got married.

This morning my wife cooked me breakfast in bed for the second time in her life, the first being this time last year. In thanks I will cook a three course meal this evening.

 

In unrelated news the BlogSpam service will be retiring the XML/RPC API come 1st January 2015.

This means that any/all plugins which have not been updated to use the JSON API will start to fail.

Fingers crossed nobody will hate me too much..

Categories: LUG Community Blogs

Chris Lamb: Starting IPython automatically from zsh

Planet ALUG - Wed, 10/12/2014 - 18:07

Instead of a calculator, I tend to use IPython for those quotidian bits of "mental" arithmetic:

In [1]: 17 * 22.2 Out [1]: 377.4

However, I often forget to actually start IPython, resulting in me running the following in my shell:

$ 17 * 22.2 zsh: command not found: 17

Whilst I could learn do this maths within Zsh itself, I would prefer to dump myself into IPython instead — being able to use "_" and Python modules generally is just too useful.

After following this pattern too many times, I put together the following snippet that will detect whether I have prematurely attempted a calculation inside zsh and pretend that I ran it in IPython all along:

zmodload zsh/pcre math_regex='^[\d\-][\d\.\s\+\*\/\-]*$' function math_precmd() { if [ "${?}" = 0 ] then return fi if [ -z "${math_command}" ] then return fi if whence -- "$math_command" 2>&1 >/dev/null then return fi if [ "${math_command}" -pcre-match "${math_regex}" ] then echo ipython -i -c "_=${math_command}; print _" fi } function math_preexec() { typeset -g math_command="${1}" } typeset -ga precmd_functions typeset -ga preexec_functions precmd_functions+=math_precmd preexec_functions+=math_preexec

For example:

lamby@seriouscat:~% 17 * 22.2 zsh: command not found: 17 377.4 In [1]: _ + 1 Out [1]: 378.4

(Canonical version from my zshrc.d)

Categories: LUG Community Blogs

Steve Engledow (stilvoid): Testing a Django app with Docker

Planet ALUG - Tue, 09/12/2014 - 01:00

I've been playing around with Docker a fair bit and recently hit upon a configuration that works nicely for me when testing code at work.

The basic premise is that I run a docker container that pretty well emulates the exact environment that the code will run in down to the OS so I don't need to care that I'm not running the same distribution as the servers we deploy to and that I can test my code at any time without having to rebuild the docker image.

Here's an annotated Dockerfile with the project-specific details removed.

# We start with ubuntu 14.04 FROM ubuntu:14.04 MAINTAINER Steve Engledow <steve@offend.me.uk> USER root # Install OS packages # This list of packages is what gets installed by default # on Amazon's Ubuntu 14.04 AMI plus python-virtualenv RUN apt-get update \ && apt-get -y install software-properties-common git \ ssh python-dev python-virtualenv libmysqlclient-dev \ libqrencode-dev swig libssl-dev curl screen # Configure custom apt repositories # and install project-specific packages COPY apt-key.list apt-repo.list apt.list /tmp/ # Not as nice as this could be as docker defaults to sh rather than bash RUN while read key; do curl --silent "$key" | apt-key add -; done < /tmp/apt-key.list RUN while read repo; do add-apt-repository -y "$repo"; done < /tmp/apt-repo.list RUN apt-get -qq update RUN while read package; do apt-get -qq -y install "$package"; done < /tmp/apt.list # Now we create a normal user and switch to it RUN useradd -s /bin/bash -m ubuntu \ && chown -R ubuntu:ubuntu /home/ubuntu \ && passwd -d ubuntu USER ubuntu WORKDIR /home/ubuntu ENV HOME /home/ubuntu # Set up a virtualenv andinstall python packages # from the requirements file COPY requirements.txt /tmp/ RUN mkdir .myenv \ && virtualenv -p /usr/bin/python2.7 ~/.myenv \ && . ~/.myenv/bin/activate \ && pip install -r /tmp/requirements.txt \ # Set PYTHONPATH and activate the virtualenv in .bashrc RUN echo "export PYTHONPATH=~/myapp/src" > .bashrc \ && echo ". ~/.myenv/bin/activate" >> .bashrc # Copy the entrypoint script COPY entrypoint.sh /home/ubuntu/ EXPOSE 8000 ENTRYPOINT ["/bin/bash", "entrypoint.sh"]

And here's the entrypoint script that nicely wraps up running the django application:

#!/bin/bash . ./.bashrc cd myapp/src ./manage.py $*

You generate the base docker image from these files with docker build -t myapp ./.

Then, when you're ready to run a test suite, you need the following invocation:

docker run -ti --rm -P -v ~/code/myapp:/home/ubuntu/myapp myapp test

This mounts ~/code/myapp and /home/ubuntu/myapp within the Docker container meaning that you're running the exact code that you're working on from inside the container :)

I have an alias that expands that for me so I only need to type docked myapp test.

Obviously, you can substitute test for runserver, syncdb or whatever :)

This is all a bit rough and ready but it's working very well for me now and is repeatable enough that I can use more-or-less the same script for a number of different django projects.

Categories: LUG Community Blogs

Christmas Meal

Wolverhampton LUG News - Mon, 08/12/2014 - 09:25
Event-Date: Wednesday, 10 December, 2014 - 19:30 to 21:30Body: It's that time of year again, so on Wednesday, 10th December 2014 at 7:30 pm we will be meeting at the Wolverhampton Cosmo Restaurant, Unit B8, Bentley Bridge Retail Park, Wednesfield Rd, Wolverhampton WV11 1BP The booking is for 7:30 - 9:30 pm so please be prompt.
Categories: LUG Community Blogs
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