January 21st, 2008 — Basic stuff
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bash (Bourne Again SHell) comes with pretty much every Unix-like OS these days. If you ever wonder what exact version of bash shell you have on your system, here's how you find out: just use the –version parameter in the command line.
Using /bin/bash to tell its version
On RedHat Linux, this is how it might look:
bash-2.05b$ /bin/bash –version
GNU bash, version 2.05b.0(1)-release (i386-redhat-linux-gnu)
Copyright (C) 2002 Free Software Foundation, Inc.
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January 15th, 2008 — Basic stuff, Unix
I've noticed how many people found other pages of this blog trying to find more information about Unix sockets, and so I thought it's about time we shed some light on this seeming mysterious, but really simple concept.
What is a Unix socket?
A Unix socket (the technically correct name for it is Unix domain socket, UDS) is a way of inter-process communication (IPC) in Unix. Like almost everything in Unix, a socket is a file. It's a special file, to be precise. Unix processes which want to communicate between each other use special set of functions to access the special file of a Unix socket, and easily exchange data in both directions.
In very simple terms, a Unix socket is nothing but a byte steam - a data transfer between processes running locally or on networked Unix systems.
January 11th, 2008 — Basic stuff
sudo allows you to run a Unix command as a different user. Using /etc/sudoers file to confirm what privileges are available to you, this command effectively elevates your access rights, thus allowing you to run commands and access files which would otherwise be not available to you.
How sudo command works
The real and effective user id (uid) and group id (gid) are set to match those of the target user as specified in /etc/sudoers file (the safest way to change this file is to use the visudo command - check out the visudo tutorial). The way you use sudo is simple enough: you run this command and specify a command line you'd like to run with the privileges of a different user. Before the requested command is run, you are asked to confirm your identify by providing your user password.
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January 9th, 2008 — Advanced topics, News, Solaris
This is a very brief introduction into navigating the device paths in Solaris. I'm using a Solaris 10 installed on Sun v490 for all the commands shown below.
Device files in Solaris
Even though all the block and character special device files are traditionally found under /dev directory, if you look closer at your Solaris 10 setup you will notice that they're not the device files themselves, but instead are just symbolic links to device files under /devices directory.
Solaris uses /devices directory for representing all the physical hierarchy of installed devices and buses found on your hardware system.
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January 3rd, 2008 — News
Looking at this website access logs, I see how many people share the same problems and look for the same solutions, but use vastly different search queries to get to my posts.
I've decided to make your life easier, and have just launched a Unix Tutorial Reference page, which is an index of pages based on your searches. Most pages will have a basic introduction to the topic and provide further pointers to the solution posts.
January 2nd, 2008 — Basic stuff, Unix
Finding the compiler version in your Unix system should be the first step before you attempt to compile any package from its source codes. In fact, if you're familiar with the common compilation routine, the configure script which you run to generate the Makefile before compiling anything does exactly that - it finds out which compilers (if any) you have installed on your system, and confirms their versions and capabilities.
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December 21st, 2007 — Basic stuff
Now and then I come across a situation when I need to run a script or a Unix command and would like to not only see the output of it on the screen, but also save this output to some log file. Redirecting the standard output using standard Unix stream redirection isn't always useful because your output will either be shown to you, or sent to the file - but not both at the same time
tee command
That's where the tee command becomes really useful. You pipe your output to this command, and let it take care of the rest.
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December 19th, 2007 — Linux, RedHat
If you're a really curious mind, you won't be satisfied with simply knowing the current release of your RedHat Linux, that's why there's a few more commands you could use to satisfy your interest.
RedHat release
If you simply want to confirm whether you're using a RHEL4, RHEL5 or any of the previous RedHat Linux releases, this is the first place to look:
bash-3.1$ cat /etc/redhat-release
Red Hat Enterprise Linux Client release 5 (Tikanga)
RedHat kernel version and type
Next step is to find out the exact Linux kernel version on your system, and also confirm whether it's 64-bit or not:
bash-3.1$ uname -a
Linux rhserver123 2.6.18-8.el5 #1 SMP Fri Jan 26 14:15:14 EST 2007 x86_64 x86_64 x86_64 GNU/Linux
RedHat kernel build
For the most curious ones, here's the last command. Use it to confirm who and when compiled the RedHat kernel you're using, and what gcc compiler was used in the build process.
bash-3.1$ cat /proc/version
Linux version 2.6.18-8.el5 (brewbuilder@ls20-bc1-14.build.redhat.com) (gcc version 4.1.1 20070105 (Red Hat 4.1.1-52)) #1 SMP Fri Jan 26 14:15:14 EST 2007
See also:
December 14th, 2007 — Unix
Quite often there's a need for you to take a screenshot of your Unix desktop, and as always there's a number of ways to do it. Today I'm going to cover the command line approach to taking screenshots.
Taking a Screenshot with xwd
Most modern Unix desktop systems come with Gnome desktop environment by default, and use Xorg as their default X11 server. This means you are likely to have the xwd tool in your OS, which allows you to take screenshots.
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December 13th, 2007 — Basic stuff, Linux, Ubuntu
visudo is a tool for safely updating the /etc/sudoers file, found in most Linux systems (Ubuntu for example).
Here's what the Ubuntu man page says about it, I think it's a great summary:
visudo edits the sudoers file in a safe fashion, analogous to vipw(8). visudo locks the sudoers file against multiple simultaneous edits, provides basic sanity checks, and checks for parse errors. If the sudoers file is currently being edited you will receive a message to try again later.
Attention: due to the sensitive content of the /etc/sudoers file, you can only run visudo as root.