Blogs

Here you can find a list of all my blogs published here.

  • Enable Wake on LAN on Windows 10
    To be able to wake up your computer via wake-up-on-lan (WOL), you need to enable this feature in the BIOS and in the Windows 10 LAN adaptor settings. Configuration: BIOS Configuration depends on the BIOS of your computer. In my case, wake up on LAN is in the power on section and disabled by default. To use this feature, just enable it. Do not forget to save the change. Configuration: Windows 10 After activating WOL in the BIOS, you need to configure Windows 10 to allow the device to wake Windows. My test computer is a Lenovo Q180 running Windows 10 German. More information on how to activate WOL for this device can be found here. Go to Network and…
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  • Block access from country by IP in Apache
    In this blog I will show how you can block access to your Apache hosted internet services, forbidding access to a whole country. The access is blocked based on the IP address of a client. In case of a VPN where the user connects to a VPN server in another country, the user will still be able to access the site. The internet is a great to ensure freedom of speech. Anyone can raise his/her voice; use the information to be informed on what is happening in the world, let others know about something, share knowledge. You can do so by using a social site or by hosting your own site. The ease of access to information; be able to…
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  • Convert SVG to PDF
    Some time ago I registered for a virtual training. The training material was made available in a web app. No PDF or a downloadable version of the material. Not a big issue, as long as I had internet access and only wanted to read the material. Problems started when I tried to access the material without a stable Internet connection. Depending where I am online is not an option. Plus point for having training material in PDF format. I can print PDF, making it easier to learn: offline, annotate pages, mark words, easier to read for the eyes. While a cloud solution is good for the vendor, it’s not always a very good option for the consumer. Taking a closer…
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  • Install SAP Web Dispatcher on Docker using SWMP
    SAP Web Dispatcher is an important component in a SAP landscape. While have been treated as optional for many years and found mainly in SAP Portal scenarios, with the increase adoption of Fiori, having a reverse proxy in the landscape is becoming pre-requisite. While it’s possible to choose from a wide range of alternatives of servers for a reverse proxy, SAP`s Web Dispatcher is normally always the best fit in a SAP landscape. A question that sometimes arises is how to install Web Dispatcher. First you settle on what version of Web Dispatcher (WD) to install. SAP Note 908097 states that you should go for the latest version. “Version 7.49 is the recommended SAP Web Dispatcher version for all backend…
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  • Parallel download of files using curl
    In a previous blog, I showed how to download files using wget. The interesting part of this blog was to pass the authentication cookies to the server as well as using the file name given by the Content-Disposition directive when saving the file. The example of the previous blog was to download a single file. What if you want to download several files from a server? Maybe hundreds or even thousands of files? wget is not able to read the location from a file and download these in parallel, neither is curl capable of doing so. You can start the download as a sequence, letting wget/curl download the files one by one, as shown in my other blog. Just use…
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  • Download files with leading zero in name using wget
    In my previous blog I showed how wget can be used to download a file from a server using HTTP headers for authentication and how to use Content-Disposition directive send by the server to determine the correct file name. With the information of the blog it`s possible to download a single file from a server. But what if you must download several files? Maybe hundreds or thousands of files? Files whose file name is created using a mask, adding leading zeros? Add leading zeros What you need is a list of files to download. I`ll follow my example from the previous post and my files follow a specific patter: number. All files are numbered from 1 to n. To make…
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  • SAPInst error java.net.InetAddress.getHostAddress
    SAPinst is used to install SAP software. You can run the installation with its graphical user interface (GUI) directly on the target host, or use a remote installation. Remote installation is normally used when the target host offers no GUI and all work is done via remote logon, like SSH. In such a setup, on the target host sapinst is started in server mode, and on the admin laptop, sapinst is started in with a GUI. The admin then connects to the target and executes the installation of SAP software remotely. Error: java.net.InetAddress.getHostAddress The setup to reproduce the error is to have sapinst running on a target host and listening on the default port 21212 and connecting to this instance…
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  • Custom 503 error page for Apache
    A 5xx error code is returned by a web server when something went wrong: The server was not able to process the request. For a reverse proxy, a common 5xx error message is 503, meaning that the backend server is not reachable. In the technical architecture of my blog site, the Wordpress site with my blogs is hosted on a Raspberry Pi in my living room, while external access is through a reverse proxy hosted on Amazon EC2. If now the reverse proxy on EC2 cannot reach my Raspberry Pi, a 503 error message is given. The root cause can be that the Raspberry Pi is turned off, there is no Internet connection available for some reason (power outage, provider problem),…
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  • Download files with wget
    A tool for download web resources is wget. It comes with a feature to mirror web sites, but you can also use it to download specific files, like PDFs. This is very easy and straightforward to do: wget <url> Example: wget http://localhost/doc.pdf This will instruct wget to download the file doc.pdf from localhost and save it as doc.pdf. It is not as easy when the weber service is requesting authentication or the URL of the PDF file ends in the same file name Authentication The documentation of wget states that you can provide the username and password for BASIC authentication. What about a web site that asks for SAML 2.0? You can pass HTTP headers to wget via parameter --header.…
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  • A start job is running for dev-disk-by
    Recently I restarted one of my Linux servers and the computer did not start up as expected. No external accessible service was running, like apache or SSH. This made the computer inaccessible from remote and left me in the dark. After a while, the server responded to ping, but nothing more. After I connected the server to a display and keyboard, I could see the error message: “a start job is running for dev-disk-by […]”. After that, Linux gave me only the option to log on in rescue mode or to restart the system. A restart didn`t help. I checked the internet and found out that the message can be caused by a fstab entry. Looking at the content of…
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