Friedrich Ewald My Personal Website

Posts

  • Improving security for SSH

    Feb 12, 2016 · 1 min read

    There are two things to increase the security for ssh logins.

    Change SSH Port

    To change the SSH port, simply edit the sshd_config file with the commmand sudo nano /etc/ssh/sshd_config and change the line Port 22 to something higher. Make sure to stay below 65,000 and don’t use any port which is already used by another service like 80 (web). After changing and saving the file, simply restart the ssh daemon and reload the configuration with sudo /etc/init.d/ssh reload. Done.

    Disable password based login for SSH

    To disable the password based login for all the users, you can do the following: 
    # Open the sshd config file
sudo nano /etc/ssh/sshd_config
    Disable password authentication with the following settings: 
    ChallengeResponseAuthentication no
    Allow private public key authentication with the following: 
    RSAAuthentication yes
PubkeyAuthentication yes
    Once this is done, restart the SSH daemon to apply the settings. 
    /etc/init.d/sshd restart
    Additional information can be found here.

  • Building a sitemap.xml with jekyll

    Feb 9, 2016 · 6 min read

    While transforming this page to Jekyll I needed a sitemap.xml for the Google Webmaster Tools. A quick search showed up this result. Works perfectly. 

    ---
layout: null
---
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd" xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  
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    <url>
      <loc>https://fewald.net/ruby/rails/2023/08/13/ruby-testing-server-part-two.html</loc>
      
        <lastmod>2023-08-13T17:44:00+00:00</lastmod>
      
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    <url>
      <loc>https://fewald.net/misc/2023/05/21/bread-recipe.html</loc>
      
        <lastmod>2023-05-21T01:30:00+00:00</lastmod>
      
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    </url>
  
    <url>
      <loc>https://fewald.net/development/python/2023/04/18/memory-profiling-memray.html</loc>
      
        <lastmod>2023-04-18T17:00:00+00:00</lastmod>
      
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    </url>
  
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    <url>
      <loc>https://fewald.net/home-improvement/2022/12/18/electric-closet.html</loc>
      
        <lastmod>2022-12-18T01:50:00+00:00</lastmod>
      
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    <url>
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        <lastmod>2022-12-11T16:25:00+00:00</lastmod>
      
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        <lastmod>2022-11-28T16:14:00+00:00</lastmod>
      
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    <url>
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      <loc>https://fewald.net/leetcode/2022/11/09/leetcode-house-robber-ii.html</loc>
      
        <lastmod>2022-11-09T20:00:00+00:00</lastmod>
      
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      <loc>https://fewald.net/leetcode/2022/11/06/leetcode-intersection-of-two-arrays-ii.html</loc>
      
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      <loc>https://fewald.net/leetcode/2022/10/27/leetcode-binary-tree-zigzag-level-order-traversal.html</loc>
      
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      <loc>https://fewald.net/ruby/rails/2022/09/15/how-to-add-devise-to-rails.html</loc>
      
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       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page15/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page16/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page17/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page18/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page19/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page20/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page21/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page22/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page23/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page24/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page25/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page26/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page27/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
    
      <url>
        <loc>https://fewald.net/page28/</loc>
        <lastmod></lastmod>
        <changefreq>weekly</changefreq>
        <priority></priority>
       </url>
    
  
</urlset>

  • Serialization and Deserialization with C# & JSON

    Feb 8, 2016 · 1 min read

    For serialization and deserialization in the .NET framework, I use the Newtonsoft JSON Serializer. This library works really fast and is very flexible. Lately I had a problem that I wanted to serialize a List<ObjA> with ObjB and ObjC. ObjB and ObjC are children of ObjA. In the code it looks as the following: 

    public class ObjA
{}

public class ObjB : ObjA
{}

public class ObjC : ObjA
{}

public class Program
{
	public void main()
	{
		List<ObjA> objectList = new List<ObjA>();

		string serializedObjects = JsonConvert.SerializeObject(objectList);

		List<ObjA> objectListNew = JsonConvert.DeserializeObject<List<ObjA>>(serializedObjects);
	}
}
    If I now serialized this with the method SerializeObject() and later deserialized it with the method DeserializeObject<>(), all the objects were of the type ObjA instead of type ObjB or ObjC. After a short research, I found the solution: 
    public class Program
{
	public void main()
	{
		List<ObjA> objectList = new List<ObjA>();

		string serializedObjects = JsonConvert.SerializeObject(objectList, Formatting.Indented, new JsonSerializerSettings()
            {
                ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
                TypeNameHandling = TypeNameHandling.All
            });

		List<ObjA> objectListNew = JsonConvert.DeserializeObject<List<ObjA>>(serializedObjects, new JsonSerializerSettings() {TypeNameHandling = TypeNameHandling.Auto});
	}
}
    This preserves the types of the objects during serialization.

  • Implementing events in List

    Feb 4, 2016 · 1 min read

    If you want to subscribe for changes to a List<T> in C# it is very easy. All you need to do, is subclass List<T> and implement your own event handler. This could be done as following: 

    using System;
using System.Collections.Generic;

namespace FEwald
{
    public class MyList<T> : List<T>
    {
        /// <summary>
        /// EventHandler which is called when items are added.
        /// </summary>
        public event EventHandler ItemAdded;

        /// <summary>
        /// EventHandler which is called when items are deleted.
        /// </summary>
        public event EventHandler ItemRemoved;

        /// <summary>
        /// Adds an item to the list.
        /// </summary>
        /// <param name="item"></param>
        public new void Add(T item)
        {
            if (ItemAdded != null)
            {
                ItemAdded(item, EventArgs.Empty);
            }
            base.Add(item);
            
        }

        /// <summary>
        /// Adds a range of items to the list.
        /// </summary>
        /// <param name="collection"></param>
        public new void AddRange(IEnumerable<T> collection)
        {
            foreach (var item in collection)
            {
                Add(item);
            }
        }
        
        /// <summary>
        /// Removes an item from the list.
        /// </summary>
        /// <param name="item"></param>
        public new void Remove(T item)
        {
            if (ItemRemoved != null)
            {
                ItemRemoved(item, EventArgs.Empty);
            }
            base.Remove(item);
        }
    }
}

  • Updating Odoo 8 to Odoo 9

    Jan 7, 2016 · 3 min read

    Currently I’m updating an odoo installation from version 8 to version 9 for a customer. In this post I will give a short introduction, on how to update the installation and most common issues I observed during the update. This post ist not complete since every odoo installation is different. First of all, there is no updater or tutorial offered by the odoo company for the community edition. The company only provides support and updates for the paid enterprise licenses. Since the database structure in odoo changed in so many fields, it is almost impossible, to update the odoo database “by hand” to version 9. The other solution, OpenUpgrade is not yet ready for the current version of the ERP system and therefore also not a possible solution. Instead, I decided to upgrade the custom developed module in a fresh odoo 9 installation. As soon as it works, I install odoo 9 with a fresh database on the server and transfer (export, then import) all the data from 8 to 9. Below is a list with possible problems and the solutions I found for them.

    Custom module isn’t shown in the list of apps

    In odoo 8, the user has to be a technical user to be able to change the technical settings. This type of user no longer exists in odoo 9. Instead, one has to activate the developer mode of odoo. This is done by clicking on the currently logged in user name in the upper right corner, then about and then “activate developer mode”. After this step, root / administrator users can update the list of apps. In my case I was able to search for my module using the search box in the upper right corner. Updating the list of apps is still necessary but it is more hidden than in the previous version.

    Using the old API

    The old API is simply no longer supported in odoo 9. My module was using it in some method signatures which I had to update to the new api style, including the method decorator @api.one and @api.multi. All the variables, like cr, context, etc. still exist but have slightly different names now.

    Using variable names in email templates

    Somehow the use of variable names as it was before is no longer possible. I will update this part as soon as I have a solution for this.

    Problems with lessc

    If lessc cannot be found it is most likely not installed on the server or, in my case, the symlink to nodejs was wrong. This is easy to fix with 
    sudo ln -s /usr/local/bin/nodejs /usr/bin/node

    Transfer old data to new database

    The data which is needed in the new database has to be transformed to match the new database structure. I my case this was done by copying the old database to a temporary database, then editing the tables exporting them, and importing them afterwards into the new database. It is important to import the data in the right order to not violate foreign key constraints. This list will be updated if new difficulties occur.

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