nixCraft » UNIX

Shell Script Wrapper Examples: Enhance the Ping and Host Commands

nixCraft — Tue, 19 Jun 2012 13:20:08 +0000

Shell script wrappers can make the *nix command more transparent to the user. The most common shell scripts are simple wrappers around third party or system binaries. A wrapper is nothing but a shell script that includes a system command or utility. Linux and Unix like operating system can run both 32bit and 64bit specific versions of applications. You can write a wrapper script that can select and execute correct version on a 32bit or 64bit hardware platform. In cluster environment and High-Performance computing environment you may find 100s of wrapper scripts written in Perl, Shell, and Python to get cluster usage, setting up shared storage, submitting and managing jobs, backups, troubleshooting, invokes commands with specified arguments, sending stdout to stdout and stderr to stderr and much more. In this post, I will explains how to create a shell wrapper to enhance the basic troubleshooting tool such as ping and host.

30 Handy Bash Shell Aliases For Linux / Unix / Mac OS X

nixCraft — Mon, 11 Jun 2012 05:58:51 +0000

An alias is nothing but shortcut to commands. The alias command allows user to launch any command or group of commands (including options and filenames) by entering a single word. Use alias command to display list of all defined aliases. You can add user defined aliases to ~/.bashrc file. You can cut down typing time with these aliases, work smartly, and increase productivity at the command prompt.

20 Examples: Make Sure Unix / Linux Configuration Files Are Free From Syntax Errors

nixCraft — Thu, 05 Apr 2012 20:00:45 +0000

In Linux and UNIX in general, services are configured using various text files,in the /etc/ directory trees. A typical server system could have dozens of configuration files. It is important that you check the validity of the configuration file. In some cases it is possible to to check the sanity of the special data (such as keys) or directories (such as /var/lib/cache/). Text files are easier to manage remotely. You can use ssh and a text editor. If there is an error in configuration, server may not start. This may result into a disaster. In this article I will explains howto find out a syntax error for popular servers and test configuration file for syntax errors.

30 Best Sources For Linux / *BSD / Unix Documentation On the Web

nixCraft — Wed, 21 Dec 2011 20:11:40 +0000

Man pages are written by sys-admin and developers for IT techs, and are intended more as a reference than as a how to. Man pages are very useful for people who are already familiar with Linux, Unix, and BSD operating systems. Use man pages when you just need to know the syntax for particular commands or configuration file, but they are not helpful for new Linux users. Man pages are not good for learning something new for the first time. Here are thirty best documentation sites on the web for learning Linux and Unix like operating systems.

Quick Tip: Find Hidden Processes and Ports [ Linux / Unix / Windows ]

nixCraft — Thu, 24 Nov 2011 10:49:51 +0000

Unhide is a little handy forensic tool to find hidden processes and TCP/UDP ports by rootkits / LKMs or by another hidden technique. This tools works under both Linux / Unix, and MS-Windows operating systems. From the man page:

It detects hidden processes using three techniques:
The proc technique consists of comparing /proc with the output of /bin/ps.
The sys technique consists of comparing information gathered from /bin/ps with information gathered from system calls.
The brute technique consists of bruteforcing the all process IDs. This technique is only available on Linux 2.6 kernels.

HowTo: Use Bash Parameter Substitution Like A Pro

nixCraft — Wed, 13 Oct 2010 22:32:02 +0000

The $ character is used for parameter expansion, and command substitution. You can use it for manipulating and/or expanding variables on demands without using external commands such as sed or awk.

10 Tools To Add Some Spice To Your UNIX Shell Scripts

nixCraft — Mon, 19 Apr 2010 20:47:43 +0000

There are some misconceptions that shell scripts are only for a CLI environment. You can easily use various tools to write GUI and/or network (socket) scripts under KDE or Gnome desktops. Shell scripts can make use of some of the GUI widget (menus, warning boxs, progress bars etc). You can always control the final output, cursor position on screen, various output effects, and so on. With the following tools you can build powerful, interactive, user friendly UNIX / Linux bash shell scripts.

Linux / Windows Application For Prevention Of RSI (Repetitive Strain Injury)

nixCraft — Wed, 04 Nov 2009 05:21:00 +0000

Repetitive strain injury (RSI) is occupational overuse syndrome, non-specific arm pain or work related upper limb disorder. RSI caused from overusing the hands to perform a repetitive task, such as typing, writing, or clicking a mouse. Unfortunately, most people do not understand what RSI is or how serious it can be. You can easily prevent RSI using open source software called Workrave.

Use a Linux LiveCD to Avoid Windows Malware For Netbanking

nixCraft — Thu, 15 Oct 2009 12:53:55 +0000

Internet has revolutionized the way online users can shop and avail banking services like internet Banking from anywhere, anytime without visiting bank. But, how safe is your money with online net-banking which allows to carry out money transfer? Companies and in some case individuals lost anywhere from $10,000 to $500,000 dollars because of a single malware infection. The cyber crooks are targeting innocent MS-Windows user. If you are concerned about how best to protect yourself from this type of fraud, use Linux LiveCD for online banking and avoid Microsoft Windows at all cost.

BIND 9 Dynamic Update DoS Security Update

nixCraft — Wed, 29 Jul 2009 15:47:12 +0000

BIND 9 is an implementation of the Domain Name System (DNS) protocols. named daemon is an Internet Domain Name Server for UNIX like operating systems. Dynamic update messages may be used to update records in a master zone on a nameserver. When named receives a specially crafted dynamic update message an internal assertion check is triggered which causes named to exit. An attacker which can send DNS requests to a nameserver can cause it to exit, thus creating a Denial of Service situation. configuring named to ignore dynamic updates is NOT sufficient to protect it from this vulnerability. This exploit is public. Please upgrade immediately.

Top 20 OpenSSH Server Best Security Practices

nixCraft — Fri, 24 Jul 2009 21:49:43 +0000

OpenSSH is the implementation of the SSH protocol. OpenSSH is recommended for remote login, making backups, remote file transfer via scp or sftp, and much more. SSH is perfect to keep confidentiality and integrity for data exchanged between two networks and systems. However, the main advantage is server authentication, through the use of public key cryptography. From time to time there are rumors about OpenSSH zero day exploit. Here are a few things you need to tweak in order to improve OpenSSH server security.

Top 10 Open Source Web-Based Project Management Software

nixCraft — Sun, 19 Jul 2009 19:18:10 +0000

Project management software is not just for managing software based project. It can be used for variety of other tasks too. The web-based software must provide tools for planning, organizing and managing resources to achieve project goals and objectives. A web-based project management software can be accessed through an intranet or WAN / LAN using a web browser. You don't have to install any other software on the system. The software can be easy of use with access control features (multi-user). I use project management software for all of our projects (for e.g. building a new cluster farm) for issue / bug-tracking, calender, gantt charts, email notification and much more.

Obviously I'm not the only user, the following open source software is used by some of the biggest research organizations and companies world wild. For e.g. NASA's Jet Propulsion Laboratory uses track software or open source project such as lighttpd / phpbb use redmine software to keep track of their projects.

6 Tools To Find Out Website Load Speed

nixCraft — Wed, 15 Jul 2009 17:42:34 +0000

Research shows that if your web pages take longer than 5 seconds to load, you lose 50% of your viewers and sales. As a UNIX admin often end users and web developers complain about website loading speed and timings. Usually, there is nothing wrong with my servers or server farm. Fancy java script and images / flash makes site pretty slow. These tools are useful to debug performance problems for sys admins, developers and end users. Here are six tools that can analyzes web pages and tells you why they are slow. Use the following tools to:

Make your site faster.
Debug site problem, especially client side and server side stuff.
Better user experience.
Improve the web.

Software Vs Hardware RAID

nixCraft — Tue, 07 Jul 2009 16:01:56 +0000

A redundant array of inexpensive disks (RAID) allows high levels of storage reliability. RAID is not a backup solution. It is used to improve disk I/O (performance) and reliability of your server or workstation. A RAID can be deployed using both software and hardware. But the real question is whether you should use a hardware RAID solution or a software RAID solution.

Download Of the Day: Firefox 3.5 For Windows, Linux, Mac OS X

nixCraft — Wed, 01 Jul 2009 05:25:00 +0000

Firefox version 3.5 has been released and available for download. Firefox 3.5 is the fastest web browser. It is twice as fast as Firefox 3. As a result javascript and multimedia enabled web apps loads faster. Firefox is the first browser to support open video and audio formats, allowing practically limitless new ways for sites to display rich content. This is based upon the open formats (HTML 5) which allow displaying media without a plug-in and/or proprietary software.

20 Linux System Monitoring Tools Every SysAdmin Should Know

nixCraft — Sat, 27 Jun 2009 02:26:39 +0000

Need to monitor Linux server performance? Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:

Finding out bottlenecks.
Disk (storage) bottlenecks.
CPU and memory bottlenecks.
Network bottlenecks.

My 10 UNIX Command Line Mistakes

nixCraft — Sun, 21 Jun 2009 02:26:29 +0000

Anyone who has never made a mistake has never tried anything new. -- Albert Einstein.

Here are a few mistakes that I made while working at UNIX prompt. Some mistakes caused me a good amount of downtime. Most of these mistakes are from my early days as a UNIX admin.

Lighttpd Traffic Shaping: Throttle Connections Per Single IP (Rate Limit)

nixCraft — Sun, 21 Jun 2009 00:02:13 +0000

If you do not control or throttle end users, your server may run out of resources. Spammers, abuser and badly written bots can eat up all your bandwidth. A webserver must keep an eye on connections and limit connections per second. This is serving 101. The default is no limit. Lighttpd can limit the throughput for each single connection (per IP) or for all connections. You also need to a use firewall to limit connections per second. In this article I will cover firewall and lighttpd web server settings to throttle end users. The firewall settings can be applied to other web servers such as Apache / Nginx and IIS server behind PF / netfilter based firewall.

Slowloris DoS Tool: It Can Bring Down Apache 1.x/2.x

nixCraft — Fri, 19 Jun 2009 14:50:39 +0000

Apache Security Update - a flaw In Apache can be used to carry out DoS. Slowloris is a new Apache DoS tool which can use slow Internet links to bring down Apache servers, rather than flooding networks. Most D/DoS tool requires faster net connections but this tool works with minimal bandwidth. This tool can lead to a DoS attack on Apache 1.x, 2.x, dhttpd, GoAhead WebServer, and Squid, while MS IIS6.0, IIS7.0, and lighttpd are confirmed not vulnerable to this attack.

Happy 40th Birthday UNIX!

nixCraft — Sun, 07 Jun 2009 18:10:03 +0000

UNIX turns 40 - in 1969 group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna developed UNIX. Today Unix offered in many flavors and developed over time by AT&T as well as various commercial vendors (such as IBM, HP, Sun, Apple etc) and non-profit organizations. CW article concluded that after four decades, the future of the operating system is clouded, but its legacy will endure in form of Linux and Microsoft NT operating system.