Blogs

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

  • 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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  • OpenSSL CA to sign CSR with SHA256 – Sign CSR issued with SHA-256
    The overall process is: Create CA Private CA key Create private key Check private key Public CA certificate Create public certificate Check public certificate Sign CSR SHA-1 Create CSR using SHA-1 Check CSR Sign CSR enforcing SHA-256 Check signed certificate SHA-256 Create CSR using SHA-256 Check CSR Sign CSR Check signed certificate Sign CSR request – SHA-256 When a CSR is created a signature algorithm can be specified. Currently, this should be SHA-256. Installing a TLS certificate that is using SHA-256 ensures that browsers like Chrome, Firefox, etc won`t show a security warning to the user. Signing the CSR using the CA is straight forward. Create CSR using SHA-256 openssl req -out sha256.csr -new -newkey rsa:2048 -nodes -keyout sha256.key –sha256…
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  • OpenSSL CA to sign CSR with SHA256 – Sign CSR issued with SHA-1
    The overall process is: Create CA Private CA key Create private key Check private key Public CA certificate Create public certificate Check public certificate Sign CSR SHA-1 Create CSR using SHA-1 Check CSR Sign CSR enforcing SHA-256 Check signed certificate SHA-256 Create CSR using SHA-256 Check CSR Sign CSR Check signed certificate Sign CSR request – SHA-1 When a CSR is created, a signature algorithm is used. Normally, this is SHA-1. Installing a TLS certificate that is using SHA-1 will give some problems, as SHA-1 is not considered secure enough by Google, Mozilla, and other vendors. Therefore, the final certificate needs to be signed using SHA-256. In case the CSR is only available with SHA-1, the CA can be used…
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  • OpenSSL CA to sign CSR with SHA256 – Create CA
    The overall process is: Create CA Private CA key Create private key Check private key Public CA certificate Create public certificate Check public certificate Sign CSR SHA-1 Create CSR using SHA-1 Check CSR Sign CSR enforcing SHA-256 Check signed certificate SHA-256 Create CSR using SHA-256 Check CSR Sign CSR Check signed certificate Create a CA To have a private CA with openssl, at least two steps are need: you need to create a private key and a public certificate. The public certificate will be used to sign CSRs. Private CA key Create private key openssl genrsa -aes256 -out ca.key.pem 4096 The command will generate a private key using random data and ask you to provide a pass phrase. While possible…
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