German Larrain on development & sys admin

[glarrain-dev-sys-blog]

How to test SMTP credentials

>>> import smtplib >>> server = smtplib.SMTP(host, port) # e.g. ('smtp.gmail.com', 587) >>> server.starttls() # if TLS is needed (220, 'Ready to start TLS') >>> server.login(username, password) (235, 'Authentication successful.')

If invalid, an exception will be raised

SMTPAuthenticationError: (535, 'Authentication Credentials Invalid')

If the server is idle too much time an exception will be raised

SMTPServerDisconnected: Connection unexpectedly closed

[glarrain-dev-sys-blog]

How to get the bytecode of a Python object

You probably know that Java and Python code isn't compiled to assembly code (by a compiler) as C code is. Instead, it is converted to bytecode. To get the bytecode of a module, class, method, function, or code object (i.e. any bytesource), use the function dis of the built-in module dis (dis is a shorthand for disassemble). (caveat: all the statements above are valid for CPython! I don't really know how these things are in Jython, IronPython or others.)

[glarrain-dev-sys-blog]

The difference of $host and $http_host in Nginx

I just posted the question and answer of this in StackOverflow. It took me a while to find it out so I guess it will useful for someone else.

[glarrain-dev-sys-blog]

Install Python 2.7 on Debian 6.0 "squeeze" amd64

Install the following packages (not all of them are mandatory but certainly are recommended) with apt-get (standard repositories):

libjpeg8-dev zlib1g-dev

libsqlite3-dev

libbz2-dev

libncurses5-dev

libreadline6-dev

Download Python 2.7.3 source code tarball.

Extract, configure, build, install:

tar xf Python-2.7.3.tgz

cd Python-2.7.3

./configure

make

make altinstall

Notice we use make altinstall, not make install. The reason is that we want to install Python 2.7 along with 2.6, not replace it (doing that would break the system, which is very bad, right?).

[glarrain-dev-sys-blog]

Use latest TortoiseHg in Ubuntu 12.04

If PPAs are updated slower than you'd like, you can use the latest version (as of today, 2.6.2) of TortoiseHg (the workbench tool to manage Mercurial repositories) quite easily.

Download latest release source code from the Download / Source page.

Extract the tarball

Install the required package pyqt4-dev-tools

Run tortoisehg-2.6.2/thg

If you like it, you can certainly install it the usual (i.e. Python packages) way.

[glarrain-dev-sys-blog]

Setup Java plugin for Chrome in Ubuntu 12.04 64-bits

Follow these instructions, NOT these. Beware that the path for "libnpjp2.so" is different if you installed the JDK instead of the JRE (included in the JDK). I did that, at this location:

/opt/java-6-oracle/jdk1.6.0_37/

Now run:

$ sudo mkdir /opt/google/chrome/plugins $ cd /opt/google/chrome/plugins $ sudo ln -s /opt/java-6-oracle/jdk1.6.0_37/jre/lib/amd64/libnpjp2.so

Restart the browser and test the plugin here.

[glarrain-dev-sys-blog]

Mixins!

Well, programming in Python suddenly mixins appear (e.g. UserDict.DictMixin) and no one told you about them! That's because this language does not really have the concept of mixins. Well, let's go look it up in Wikipedia. Aha, it has its own article: Mixin. For me, what cleared up the whole thing was this phrase: "A mixin can also be viewed as an interface with implemented methods." In StackOverflow there is a good question about this topic: What is a Mixin, and why are they useful? Well, not everything is pretty with mixins. Some critiques here: Mixins considered harmful/1 and Mixins considered harmful/2

[glarrain-dev-sys-blog]

How to sort a list randomly

Easy wheezy

import random people = ['j', 'r', 's', 'a', 'k'] random.shuffle(people) print(people)

[glarrain-dev-sys-blog]

How to create source distributions for a Python package and upload them to PyPI

To create a source distribution, the following command yields the most basic result. python setup.py sdist which is a gzipped tar in *NIX systems or a zip file in Windows.

To upload the generated distribution to the Python Package Index (PyPI), python setup.py sdist upload is enough.

However, how can we generate both gzip and zip archives and upload them no matter the OS we are using? python setup.py sdist --formats=gztar,zip python setup.py sdist --formats=gztar,zip upload

[glarrain-dev-sys-blog]

Ubuntu to Lubuntu, Gnome-keyring and Chromium

I switched from Ubuntu to Lubuntu, mostly because I was disappointed with the DE (Desktop Environment). I surf the web all day, with dozens of tabs at the same time. Firefox used to be my choice but got so slow (and Chromium so fast) that I abandoned it.

Many websites require passwords, and most of them are not really as important as a bank account so I save them in gnome-keyring through Chromium (BTW, if you do that in Firefox and have not set a master password, then all you passwords are stored in plain text to be seen by anyone. You might now believe it but it is true), which helps a lot.

Sadly, after I switched to Lubuntu, Chromium wouldn't access the stored keyring or list any of my passwords (which could very well be over a hundred).

Inspired by this thread, I started the browser with the option set to use the gnome-keyring.

$ chromium-browser --password-store=gnome

... (some debugging info)

[5236:5250:2716672659:ERROR:native_backend_gnome_x.cc(664)] Keyring find failed:

All right, then I had to go to seahorse (Chromium was closed. Make sure it is not running in the background; it shouldn't appear in the system tray) Two keyrings were listed: "default" and "login". Unlock "login", delete it. Change password of "default" to your login password. Notice that all your saved passwords are there (under the "default" icon)! Lock it and close seahorse.

Start Chromium in the same way as before, and the "keyring find failed" error shouldn't appear. You will be prompted for the keyring password when it starts or if you go to a login page of a website matching a password stored in the keyring.

That's it.

[glarrain-dev-sys-blog]

Migrating a Linux server

Articles from Rackspace's Knowledge Base.

Migrating a Linux Server From the Command Line

Stage 1 Stage 2 Stage 3 Tips For Speeding Up Rsync

My procedure

A: source PC, B: target PC. Tested for ubuntu server 10.04 amd64

Check OS system version and other useful info A$ uname -a

Install the same system (clean, obviously) in B.

Log as root in B

Update repositories. B$ apt-get update

Update packages B$ apt-get upgrade

B$ reboot

Log as root in B

(again) Update repositories. B$ apt-get update

(again) Update packages B$ apt-get upgrade

Save in a text file a list of installed packages in A A$ dpkg --get-selections > installed_packages.txt

Copy installed_packages.txt from A to B. If both are remote, use FTP over SSH to both PCs or use rcp.

Load installed_packages.txt into package manager B$ dpkg --set-selections < /root/installed_packages_2012.07.23.txt

Install them B$ apt-get dselect-upgrade

B$ reboot

Create (in A) a file with all the directories and file to be excluded from replication. Some HAVE to be excluded (such as /boot, /proc and /dev) while others should be excluded. Me? This is my basic list:

/boot /proc /sys /tmp /dev /var/lock /etc/fstab /etc/mdadm.conf /etc/mtab /etc/resolv.conf /etc/conf.d/net /etc/network/interfaces /etc/networks /etc/sysconfig/network /etc/sysconfig/network-scripts /etc/sysconfig/hwconf /etc/sysconfig/ip6tables-config /etc/sysconfig/kernel /etc/hostname /etc/HOSTNAME /etc/hosts /etc/modprobe* /etc/modules /etc/udev /net /lib/modules /etc/rc.conf /lost+found /mnt /media /var/cache/apt/archives

Fill the file with your choices A$ nano exclude_from_rsync.txt 

Run rsync in test mode ("dry run"). IPB: IP address of B A$ rsync -e 'ssh -p 22' --dry-run -azPx --exclude-from="exclude_from_rsync.txt" / root@IPB:/

See what will be transferred. If you notice something you would rather skip, add another entry to exclude_from_rsync.txt

Run the same command without  --dry-run

That's it! You can run it again and again and only the changed files will be transmitted (rsync is quite smart).

If you were logged in in B, reboot, and try to login. You will notice the password is now the same as the one in computer A.

Congrats

[glarrain-dev-sys-blog]

How to ping a specific port

You can't. Or you can, but it is not "pinging" really. For that, you will need the nmap program (apt-get install nmap on Ubuntu).

Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing.

Use cases:

"Ping" a port nmap -p 80 example.com

Scan ports nmap example.com

Sources: http://serverfault.com/questions/309357/ping-a-specific-port nmap man page