Linux Developer Notes - Tips, Tricks, Hacks and How-To's

About this site...

btilma — Wed, 24 Dec 2008 21:33:24 -0600

This site is under active development, and articles are added all the time, so feel free to leave feedback and stop back or subscribe to new content. It started as a private collection of hacks and howto's. In the course of my work, I've been called upon to venture into many areas of linux development and administration, and been faced with a veritable cornucopia of challenges. Sometimes, I have been known to *forget* how I did something, and find myself compelled to re-discover it, either for myself or someone else. In an effort to categorise these little bits of occasionally hard-won knowledge, both for myself and so that I can simply point others to it when they wish to know something I've already figured out, I put this site together. Since then, I've been privileged to acquire titbits from others as well, and have added them to the collection.

Grabbing a Remote User's Display with x11vnc

btilma — Wed, 07 Jan 2009 02:19:19 -0600

Let's consider a scenario. You've got a user of your software who's struggling with how to do something. You know if you were there, you could show them very quickly, but trying to explain via telephone or email is proving really difficult. Or perhaps you need to interact with a remote display for some other reason, such as running graphical software on the remote machine with the option to detach from the session with the software still running, and be able to pick it up again when you're in front of the machine. You also might have left some software or website open on your screen and decide you need to close it. All of these scenarios could be challenging to you, linux being a multi-user operating system and all. It's designed to allow multiple users access to the machine without running into each other, but what if you want to run into each other?

Connecting To a PPTP Server From the Command Line

btilma — Mon, 05 Jan 2009 02:24:00 -0600

There are many different flavors of pptp clients, most of them graphical. Although if you're unfortunate enough to be on a MS (Windows) system, you're stuck with theirs and all of its limitations, those of us who are fortunate enough to be working on linux can do much better. This article will focus on setting up PPTP (Point-To-Point Tunnelling Protocol) clients from the command line. The huge advantage that we gain by switching to the CLI (Command Line Interface), is that we're no longer limited in the number of open connections we can have. It's also a very great deal faster to use the command line, both for setup and connection, and it's really quite simple.

Using SSHFS

btilma — Wed, 31 Dec 2008 01:30:21 -0600

Although it's relatively simple, I thought I'd write a brief article on the use of sshfs, because it's such a helpful tool. First, you'll need to have sshfs and fuse installed. You can get them here(sshfs) and here(fuse). The server (remote) side doesn't need anything but sshd (ssh server) installed. The beauty of the whole arrangement is that sshfs is really just a kind of wrapper around ssh/sftp, so the server doesn't even need to know about any permissions other than the standard ssh login. You can mount any path from the server that you have access to via ssh. Using sshfs from the command line is really easy. To mount a filesystem, you'll want to do so as your standard user (not root). Simply do:

sshfs user@host: <mountpoint>

and to unmount:

fusermount -u <mountpoint>

Creating a Self-installing Executable Shell Script

btilma — Mon, 29 Dec 2008 18:10:35 -0600

This How To will cover creating a shell script that contains your installable product inside of it and can be used to install your product on a target machine. This is essentially one file that contains both the files to install and the install logic within it. You'll need a few tools to start off with, namely

uuencode

and

uudecode

These are historical unix tools. From the wikipedia page, at http://en.wikipedia.org/wiki/Uuencode

Passwordless SSH logins

btilma — Fri, 26 Dec 2008 22:26:35 -0600

To enable login to a remote machine by ssh without having to enter the password is a useful thing, and one I get asked about with some regularity. I'll describe two methods I use, one that uses ssh public keys with no passphrases, and the other using ssh-agent to store the passphrases of your keys.

To use ssh keys, you'll first need to have one. You can create this with the ssh-keygen utility like so:

ssh-keygen -t <algorithm> -b <bit size>

for example:

ssh-keygen -t rsa -b 4096

Grepping with Vim

btilma — Wed, 07 May 2008 22:48:20 -0500

Of the many productivity-enhancing features that Vim has, one the the best for making similar changes to many files is grep, or vimgrep. This handy little tool will, from within vim, tell you how many files match your pattern, and then proceed to take you to each match, regardless of which file it occurs in. Sure, for straight /pattern/replacement/ text, there's nothing like sed -i, but if you've got to make changes which are similar or to similar areas but not the same, then vimgrep is your friend. To invoke this, you have two basic options. From the command line:

Enabling Unrecognized Serial Ports

btilma — Mon, 21 Apr 2008 22:53:14 -0500

Sometimes, you've got a serial card that isn't included in the kernel's list of known devices for some reason. It could be that it is just a very small manufacturer, or perhaps the card you've got is newer than the kernel you've got. In either case, as long as the card you have is a 16550 UART, you should be fine. This little gem will get your card recognized and working smoothly. First, you've got to see if your card is even seen by the kernel. You can do this with

lspci

If the kernel lists it as an 'Unknown' device, then it won't show up in

Shell Commands with Sed

btilma — Mon, 21 Apr 2008 22:15:29 -0500

Sed, that most useful of pattern replacement tools, can be used for much more than simple string replacements in text files. This article will examine the uses of Sed for creating commands and feeding them to the shell. This can be extremely useful, especially when working on file manipulations for large batches of files at a time. Let's say for example that you've got a directory full of files, and you'd like to move them into subdirectories according to the first three characters of the filenames. This is a one-liner with sed.

Java and Compositing Window Managers

btilma — Tue, 08 Apr 2008 22:25:42 -0500

Java applications with graphical user interfaces still don't play well with compositing window managers such as Compiz or Compiz-Fusion. Frequently the java application window will open, but remain blank. Fortunately, the fix for this is relatively simple. Exporting the variable "AWT_TOOLKIT=MToolkit" before running the jvm will fix this problem. If your java application has a menu entry or a desktop icon, you can make the necessary changes to the properties of the .desktop file by specifying the command as