Category: Linux

Solution for Executing Native Process from Java that Requires sudo

Posted on by rchapin

If you are building a Java program that requires the ability to execute native commands on the machine which require sudo it requires some additional considerations other than just writing the Java code.

The problem is that sudo, by default, requires a tty for executing sudo such that a password can entered.  Even if you configure sudoers to grant NOPASSWD access to a specific command you will still get the following error

sudo: sorry, you must have a tty to
→ Continue reading “Solution for Executing Native Process from Java that Requires sudo”

Blacklisting Kernel Modules

Posted on by rchapin

Following is a walkthrough on how to blacklist a kernel module.  The specific example is blacklisting the nouveau driver so that I can install the OEM Nvidia driver.

1. First, blacklist the nouveau driver: Add a line to the textfile /etc/modprobe.d/nouveau-blacklist.conf that contains they keyword ‘blacklist’ and the name of the driver

blacklist nouveau

2. Rebuild the initramfs image file.  First, backup existing initramfs

mv initramfs-3.10.0-327.18.2.el7.x86_64.img initramfs-3.10.0-327.18.2.el7.x86_64.img_2016-06-09.bak

Build new initramfs

dracut -v /boot/initramfs-$(uname -r).img $(uname -r)

3. Reboot the system → Continue reading “Blacklisting Kernel Modules”

Using netcat to Mock a RESTful Webservice that Returns JSON

Posted on by rchapin

Let’s say that you are working on a part of a project that needs to consume some JSON data from a forthcoming HTTP service.  That sub-system is being developed by one of your colleagues and is not yet ready for you to stand-up to develop against.

You can use netcat to mock the webservice and return some static JSON data for which you can develop and test against with a simple one-liner.

First, put together your JSON in a file, → Continue reading “Using netcat to Mock a RESTful Webservice that Returns JSON”

How to Use Credentials That Contain Special Characters with curl

Posted on by rchapin

In order to execute curl commands to endpoints with passwords that contain special characters, the cleanest way that I have found to do so is to Base64 encode the authentication string for curl and then pass an Authorization request header along with the request.

In this example the credentials are uid ‘rchapin’ and passwd ‘abc123!@#’.  Normally we would pass this to curl as follows:

$ curl -u rchapin:abc123!@# -X GET https://some-endpoint:443

However, this will not work and the password will → Continue reading “How to Use Credentials That Contain Special Characters with curl”

How to Configure a Linux Client for Active Directory Authentication

Posted on by rchapin

I am currently working on setting up multiple environments for a new project (DEV, QA, and PROD) and will be integrating all of the servers to an Active Directory Domain Controller for user management.

Following are notes from when I configured a Fedora Core 18 laptop to integrate with an AD server.  It is likely things have changed some from then and I will update this as required for a current version of RHEL7/CentOS 7.

Install the following packages

yum
→ Continue reading “How to Configure a Linux Client for Active Directory Authentication”

[SOLVED] Delete key not working with x2go server running XFCE

Posted on by rchapin

I am working with a development environment whereby I VPN into an environment with an Ubuntu VirtualBox guest and then initiate an x2go client session to a developement workstation server that lives in the development environment.

I had everythining working exactly as I wanted except that the Delete key did not work in the x2go session.

Previously the xev output when pressing the delete key was:

FocusOut event, serial 36, synthetic NO, window 0x2e00001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event,
→ Continue reading “[SOLVED] Delete key not working with x2go server running XFCE”

Looping Through a List of Files with Spaces in the File Name with Bash

Posted on by rchapin

If you have a list of files that you want to operate on in a loop in bash and some of them have spaces in the file name the default IFS (Internal Field Separator) will match with the space and tokenize the file.

The simple approach is to temporarily set the IFS as follows.  This can be done in a shell script, but the following example is directly on the command line for ‘one-liner’ usage.

OIFS="$IFS"

IFS=$'\n' 

for i in
→ Continue reading “Looping Through a List of Files with Spaces in the File Name with Bash”

How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files

Posted on by rchapin

The easiest way that I have seen so far for doing so is to use tail and simply read everything except the first three bytes (start reading at the 4th byte), as follows:

tail --bytes=+4 text_file.txt text_file-wo-bom.txt
→ Continue reading “How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files”

Perl One-Liner for Replacing Multiple Lines of a Text file With Multiple Lines of Text

Posted on by rchapin

When executing ‘search-and-replace’ commands on ASCII under Linux, Unix (or *nix) operating systems, sed works or most cases and makes for reasonably straightforward reading of the script.

If  you want to replace multiple lines of text with multiple lines of text, following is a perl one-liner that does the trick and is much easier to wrangle than trying to do it in sed.

perl -i -pe "BEGIN{undef $/;} s:${EXISTING_LINES}:${REPLACEMENT_TEXT}:smg" file.txt
→ Continue reading “Perl One-Liner for Replacing Multiple Lines of a Text file With Multiple Lines of Text”

Adding the Contents of a Source File to the Beginning of a Target File

Posted on by rchapin

Following is *nix a command that you can use to add the contents of a source text file to the start of another text file (the source file).

echo -e '0r <source_file_name\nw' | ed -s <target_file_name
→ Continue reading “Adding the Contents of a Source File to the Beginning of a Target File”
© 2005 Ryan Chapin