Run only a single instance of a cron job and prevent overlap

When dealing with web applications often a cron process must be executed at most once. If a cron job overlaps, database queries can cause performance issues or at worse deadlocks and stale processes.

Here is a script that solves this problem. Explained with detail as there are a lot of things happening in 5 lines of code.

#!/bin/bash

# Installation
# mkdir /var/run/moodle
# chown root.apache /var/run/moodle
# chmod 775 /var/run/moodle
# copy this file and make it executable by the cron user. 

# chmod this file 744

# add it to crontab or crontab -e -u apache 

# Explanation
# 1. set -e tells a bash script to exit whenever a non zero value is i
#  returned (0 means function executed without error)
# 2. flock needs 200 or any int to label the file descriptor
# 3. The ( brackets ) execs each line of commands in order and check to 
#  see if they return 0. 
# 4. 200> tells the fd 200 to create the lock file if it doesn't already 
#  exist 
# 5. -n nonblock, will return 1 if the lock is taken. as cron is being 
#  ran every 5-10 mins we can wait for the next one
# 6. trap, if cntrl-c is called or a command is killed, it will execute 

#  the command and exit. Our case it removes the lock file.

# Note: This works great for cron and flock files. May be an issue with 

#  race conditions if something other than flock eg. echo 'busy' > file.pid.

LOCKFILE=/var/run/moodle/moodlecron.lock
set -e
(
    flock -n 200 
    trap "rm $LOCKFILE" EXIT 
    # Add commands to execute
    /usr/bin/php /var/www/html/moodle/admin/cli/cron.php  
) 200>$LOCKFILE

Get your page to highlight in Moodle's navigation Menu

Moodle 2.3+ is able to automatically determine the menu items to highlight in the navigation menu. While working on one of my current projects, I was unable to make the current page highlight and I went looking for the Moodle method that do this.

I have a custom reports module that is located in report/mycustomreports

To add a custom report specific to a course and under the report menu item you add this bit of code to lib.php file.

// File report/mycustomreport/lib.php

function report_mycustomreports_extend_navigation_course($navigation, $course, $context) {
    global $CFG, $OUTPUT;
    if (has_capability('report/mycustomreports:viewcoursereports', $context)) {
        $url = new moodle_url('/report/mycustomreports/course/index.php', array('id'=>$course->id));
        $navigation->add(get_string('mycustomreports', 'report_mycustomreports'), $url, navigation_node::TYPE_SETTING, null, null, n
ew pix_icon('i/report', ''));
    }
}

Take note of the URL and how it will end up looking:
example.com/report/mycustomreports/course/index.php?id=55

Now to make sure that the link to this report in the courses menu receives a highlight and expands the window, you must add a $PAGE->set_url() in the index.php

// File: report/mycustomreports/course/index.php

$PAGE->set_url('/report/mycustomreports/course/index.php', array('id' => $course->id));

Both URL's now match.

If we click on the [Course Name] -> Reports -> My Custom Reports the page will load AND most importantly the link in the navigation menu will be highlighted.

Passwordless login with multiple id_rsa and ssh identities

Primarily for my benefit as this topic can be found on tons of google searches. I have different user names such as ~bunwich and ~sandwich on a variety of servers. I want to be able to login without a password by entering ssh bunwich@example1.com or ssh sandwich@example2.com

On my computer, I have two different id_rsa, one for each account. (Also the corresponding id_rsa.pub) The goal is to automatically choose the correct id_rsa for each username and login without a password.

1)  ssh allows you to manage multiple identies using a wild cards and filtering by remote hostname and remote username. You can also filter by local hostname and local username.

From the manual
"The file name may use the tilde syntax to refer to a user's home directory or one of the following escape characters: '%d' (local user's home directory), '%u' (local user name), '%l' (local host name), '%h' (remote host name) or '%r' (remote user name)."

2)  Create the following dirs

~/.ssh/ids/bunwich

~/.ssh/ids/sandwich

3) Copy the id_rsa belonging to each user into these dirs

~/.ssh/ids/bunwich/id_rsa

~/.ssh/ids/sandwich/id_rsa

chmod id_rsa to 600 if it isn't already

4)  Add an IdentityFile entry to you  ssh config file

vim ~/.ssh/config

Add the following line:

IdentityFile ~/.ssh/ids/%r/id_rsa
 

An alternative is to also include a host name for each username.

eg.

IdentityFile ~/.ssh/ids/%h/%r/id_rsa 

5) Now make sure that both servers example1 and example2 have a ~/.ssh/authorized_keys and you'll be able to do passwordless logins.

(You create authorized_keys by renaming the id_rsa.pub or appending the id_rsa.pub to the current authorized_keys)



Extra - While you're messing with your config file, why not add an extra visual measure to make sure your host hasn't changed.

VisualHostKey yes to ~/.ssh/config

Solution to Atheros AR9285 Wireless Card - Pinging works, but browsing the web does not.

A few years back I purchased a Compaq CQ62-215DX notebook for $300.00. Based on the AMD V120 CPU, it is all the power you need to watch movies, run microsoft word an surf the web.

Recently I updated some drivers, or I think I did during a routine Windows Update, and afterwards I was unable to surf the web. I was able to ping google.com/yahoo.com, but could not retrieve pages for major web sites. Other laptops worked so I knew it wasn't a router issue.

Doing a search yielded plenty of results with people having the same problem.

System: 

Windows 7 64-bit Home Edition

Netgear WNDR3700 - has b/g/n and supports 2.5 and 5ghz. 150mbps to 300 mbps.

Compaq CQ62-215DX Atheros AR9285 b/g/n

Step 1: Try all the drivers available for this card

There are about 2-3 driver packages on hp.com and the sketchy www.atheros.cz site.

Link to the Atheros 2011 drivers sp52131.exe
Link to atheros.cz drivers

I probably installed these 20 times and still got no connectivity. Not to mention the Auto Update Installation on Windows 7 home would keep trying to install the old drivers without my permission. (gpedit.msc is not available on windows 7 home which lets you stop this from happening).

Step 2: Found a post with a possible solution

After spending a few days researching, I stumbled upon a post on the hp forums where a user who had an ASUS laptop turned off the Wireless Mode from Auto to b/g and then was able to connect.

Problem is when you go to device properties for your wireless network card you may not have a Wireless Mode setting. I reinstalled all the old drivers to see if there was a wireless mode setting in previous versions and nope, HP did not make these settings available.

Step 3: Look at the .inf files

The next step was to determine where in the registry the advanced settings for the atheros wireless card were located. Long story short I was able to track the location of the registry keys used to configure the device, and I found a bunch of registry settings in the .inf files from the atheros.cz drivers. Next would be to add the registry settings to my Windows 7 registry.

Solution

TLDR; Wireless N did not work on the AR9285. Might be hardware, might be drivers. Whatever is I had to turn it off so that I could at least connect to the internet.

I first tried to unpack the driver packages and modify the .inf files so I could get the setup.exe to do this for me. After a few failed attempts I gave up trying to automate key registration, and instead went with hand editing the registry. (yes regedit.exe can blue screen/kill your computer so be careful)

From the .inf file in the atheros.cz we have these settings.

HKR, Ndi\params\NetBand,     ParamDesc, 0,  %WirelessMode%
HKR, Ndi\params\NetBand,     Base, 0,  "10"
HKR, Ndi\params\NetBand,     default, 0, "26636"
HKR, Ndi\params\NetBand,     type, 0,  "enum"
HKR, Ndi\params\NetBand\enum, "26636", 0,  %WirelessModeAuto%
HKR, Ndi\params\NetBand\enum, "12",  0,  %WirelessMode11bgOnly%

[Strings]
WirelessMode                 = "Wireless Mode Selection"
WirelessMode11bgOnly         = "802.11b/g"
WirelessModeAuto             = "Auto"

Step 4: Enter these in the registry in the right place - good luck with that

To find where, I did a search for "Adhoc 11n" in regedit.exe. This is one of the settings you can choose for your drivers and it seemed unique enough. I only found two cases of this in my registry so I decided to add the above keys and values next to the Adhoc 11n. One of these had to be the correct settings for my device. Lucky for me the first one I chose happened to be the right one.

This is how your registry should look. (Yeah you can't see the Adhoc 11n, but it's within the htAdhocEnable)

Create a key called NetBand, and add each value as a string. You can compare the format to the shortPreamble above it which is a setting that was installed by the driver. (If you don't trust me look at the .inf file from atheros.cz)

Next create a sub key within NetBand called enum. This is where you get to choose Auto or Wireless b/g

After doing this, go to your wireless network card, click properties, configure, advanced and you should now be able to choose b/g or auto.

Set it to 802.11 b/g and hit OK. Your wireless connection will restart and hopefully you will now be able to connect. It did for me. Woot!

NOTE: For those who have a little more time and effort, or maybe someone at HP can figure this out - change the .inf file and add above registry fields so we can configure the Wireless Mode. This would save a lot of people time and effort.

Install 389 in Fedora 16 Starting and Stopping LDAP

Refer to this page for some info about starting and stop the 389 server.
http://directory.fedoraproject.org/wiki/Howto:systemd

1) To setup the system for testing add an entry into your /etc/hosts such as

127.0.0.1 example.com 

2) To install 389 add the packages to fedora 16.

3) Run the command sudo setup-ds-admin.pl There is a setup-ds.pl but that I believe sets up separate ldap servers and not config the entire system including the admin.

4) When it asks for a host, it will give something like example.com.locahost Enter example.com

5) Enter the domain.

On mine it asks for dc=com. I entered instead dc=example,dc=com

6) Answer the remaining questions and complete the installation
(If you make a mistake run sudo remove-ds-admin.pl)

7) To connect to 389 as an admin

run 389-console 

Enter User ID: dc=Directory Manager 

Passsword: [whatever u entered during the setup process] Administration 

URL: http://localhost/9830 

If you have problems use the java from sun instead of openjdk.
(google java sun alternatives linux)

---

Starting and Stop the service.


1) Start the 389 admin service

service dirsrv-admin start

This however starts up the admin portion of 389 and not the ldap server that stores data.

2) Start your 389 ldap service

I usually use service to start and stop my services

sudo service dirsrv@example start

With fedora 16, I'm finding that I'm using systemctl more often

This will also start and stop the dirsrv service

sudo systemctl start dirsrv@example

To start and stop all your ldap services

sudo systemctl start dirsrv.target

3) The ldap server does not start on boot.

Current unsure why service dirsrv start does not work.

 -

rails spork autotest failures repeating endlessly

Rails 3.1
Spork 0.9 rc9
ZenTest (installs autotest binary)
Fedora Linux

After launching spork, and then autotest, any failed tests will continuously get retested by autotest. This is because autotest is looking for changes in file dates and will rerun all tests if it finds a change.

Solution:

.autotest setup can be found in
http://ruby.railstutorial.org/chapters/static-pages
and
http://automate-everything.com/2009/08/gnome-and-autospec-notifications/

Edit ~/.autotest

  Autotest.add_hook :initialize do |autotest|
    autotest.add_exception %r{^\.git}  # ignore Version Control System
    autotest.add_exception %r{^./tmp}  # ignore temp files
    autotest.add_exception %r{^./log}  # ignore log

    # from rails tutorial 201109
    autotest.add_mapping(/^spec\/requests\/.*_spec\.rb$/) do
      autotest.files_matching(/^spec\/requests\/.*_spec\.rb$/)
    end 
  end


I had to add the log exception to stop the failure cycle.

rails, devise and how to edit user account profile without providing a password

There are several options on the wiki to update an account information without providing a password

https://github.com/plataformatec/devise/wiki/How-To%3a-Allow-users-to-edit-their-account-without-providing-a-password

This is due to the fact that devise is asking for the current password for all profile changes. The wiki makes changes to remove password fields or the current password from the form.

The workflow I was looking for was to allow the user to change details such as first and last name without a password. Only when the current password is change is a password required.

Solution:
rails 3.1
devise 1.4.4
From the Gem

/gems/devise-1.4.4/lib/devise/models/database_authenticatable.rb

copy the method update_with_password and add it to your user.rb model (or whatever model you're using to store account information)

      def update_with_password(params={})
        current_password = params.delete(:current_password)

        if params[:password].blank?
          params.delete(:password)
          params.delete(:password_confirmation) if params[:password_confirmation].blank?
        end

        result = if valid_password?(current_password)
          update_attributes(params)
        else
          self.attributes = params
          self.valid?
          self.errors.add(:current_password, current_password.blank? ? :blank : :invalid)
          false
        end

        clean_up_passwords
        result
      end

Next change the line

result = if valid_password?(current_password)

to

result = if params[:password].blank? && if params[:password].blank? || valid_password?(current_password) 

Don't check for current password if password is blank, go ahead and update