はてなブックマーク

10 Tips for C and C++ Performance Improvement Code Optimization When you start writing your code in C, C++ or any other programming language, your first objective might be to write a program that works. After you accomplished that, the following are few things you should consider to enhance your program. Security of the program Memory consumption Speed of the program (Performance Improvement) This

How to Speedup Linux Boot Process using Startpar Command Examples In a typical scenario, during the boot process, the run-level system startup scripts are executed one-by-one. A particular run level startup script will not execute until the previous script is executed completely. If a particular service during the startup is hanging for some reason, it might take a while before it times-out and mo

HPACUCLI stands for HP Array Configuration Utility CLI. As the name suggests, this utility is for HP servers. Hpacucli is used to create, delete and repair the logical and physical drives on the smart array controllers in HP servers. To use hpacucli, download and install the latest version of hpacucli rpm from the HP website on your Linux server. 1. Two ways to execute the command When you type th

How to Write Your Own Linux Kernel Module with a Simple Example What are kernel modules? Kernel modules are piece of code, that can be loaded and unloaded from kernel on demand. Kernel modules offers an easy way to extend the functionality of the base kernel without having to rebuild or recompile the kernel again. Most of the drivers are implemented as a Linux kernel modules. When those drivers ar

How to Combine Ping and Traceroute On Linux Using MTR Command Examples MTR stands for My Traceroute. It is a powerful network diagnostic tool which combines the power of both Ping and Traceroute commands. It enables administrator to diagnose and isolate network errors and provide helpful network status reports. In this article, we will explain how to install, use and analyze the report provided by

This tutorial explains various command line options available for the Linux shutdown and reboot commands. Linux shutdown command options Syntax: shutdown [OPTION]… TIME [MESSAGE] From the syntax we see that besides OPTIONS and TIME, there is a MESSAGE that can be produced on the command line through this command. Please note that you need to have root privileges to execute this command. 1. A basic

Interrupts are signal that are sent across IRQ (Interrupt Request Line) by a hardware or software. Interrupts allow devices like keyboard, serial cards and parallel ports to indicate that it needs CPU attention. Once the CPU receives the Interrupt Request, CPU will temporarily stop execution of running program and invoke a special program called Interrupt Handler or ISR (Interrupt Service Routine)

The xargs command is extremely useful when we combine it with other commands. This tutorials explains the usage of xargs command using few simple examples. These example will help you understand the basics of how xargs command works. But, once you understand these concepts, you can come-up with your own clever examples of xargs to solve various command line problems. Syntax of xargs (from the man

Reverse SSH is a technique that can be used to access systems (that are behind a firewall) from the outside world. As you already know SSH is a network protocol that supports cryptographic communication between network nodes. Using this protocol, you can do a secure remote login, secure copy from/to a remote machine etc. You’ll typically do the following to connect to a remote server securely usin

10 Practical Linux Cut Command Examples to Select File Columns Linux command cut is used for text processing. You can use this command to extract portion of text from a file by selecting columns. This tutorial provides few practical examples of cut command that you can use in your day to day command line activities. For most of the example, we’ll be using the following test file. $ cat test.txt ca

Cat command is one of the basic commands that you learned when you started in the Unix / Linux world. You already know that cat displays a file content. What more could this command do? This tutorial gives 10 practical usage examples for cat command. Probably few of these examples could be new to you. Or, it might just be a refresher for you, if you already knew these examples. 1. Display the cont

GCC Compiler is a very powerful and popular C compiler for various Linux distributions. This article explains some of the popular GCC compiler options. An Example C Code The following basic C code (main.c) will used in this article : #include<stdio.h> int main(void) { printf("\n The Geek Stuff\n"); return 0; } GCC Compiler Options 1. Specify the Output Executable Name In its most basic form, gcc c

lsof stands for List Open Files. It is easy to remember lsof command if you think of it as “ls + of”, where ls stands for list, and of stands for open files. It is a command line utility which is used to list the information about the files that are opened by various processes. In unix, everything is a file, ( pipes, sockets, directories, devices, etc.). So by using lsof, you can get the informati

In this article, we will discuss some interesting problems on C language that can help students to brush up their C programming skills and help them prepare their C fundamentals for interviews. 1. gets() function Question: There is a hidden problem with the following code. Can you detect it? #include<stdio.h> int main(void) { char buff[10]; memset(buff,0,sizeof(buff)); gets(buff); printf("\n The b

Q: How do I encrypt my bash shell script on Linux environment? The shell script contains password, and I don’t want others who have execute access to view the shell script and get the password. Is there a way to encrypt my shell script? A: First, as a best practice you should not be encrypting your shell script. You should really document your shell script properly so that anybody who views it und

Netcat or nc is a networking utility for debugging and investigating the network. This utility can be used for creating TCP/UDP connections and investigating them. The biggest use of this utility is in the scripts where we need to deal with TCP/UDP sockets. In this article we will learn about the netcat command by some practical examples. 1. Netcat in a Server-Client Architecture The netcat utilit

2 Types of Linux File Locking (Advisory, Mandatory Lock Examples) File locking is a mechanism which allows only one process to access a file at any specific time. By using file locking mechanism, many processes can read/write a single file in a safer way. In this article we’ll explore the different types of Linux file locking and understand their differences using an example program. We will take

HowTo: The Ultimate Logrotate Command Tutorial with 10 Examples Managing log files effectively is an essential task for Linux sysadmin. In this article, let us discuss how to perform following log file operations using UNIX logrotate utility. Rotate the log file when file size reaches a specific size Continue to write the log information to the newly created file after rotating the old log file Co

How To Backup and Restore PostgreSQL Database Using pg_dump and psql This is a guest post written by SathiyaMoorthy pg_dump is an effective tool to backup postgres database. It creates a *.sql file with CREATE TABLE, ALTER TABLE, and COPY SQL statements of source database. To restore these dumps psql command is enough. Using pg_dump, you can backup a local database and restore it on a remote datab

The nm commands provides information on the symbols being used in an object file or executable file. The default information that the ‘nm’ command provides is : Virtual address of the symbol A character which depicts the symbol type. If the character is in lower case then the symbol is local but if the character is in upper case then the symbol is external Name of the symbol The characters that id

Dig stands for domain information groper. Using dig command you can query DNS name servers for your DNS lookup related tasks. This article explains 10 examples on how to use dig command. 1. Simple dig Command Usage (Understand dig Output) When you pass a domain name to the dig command, by default it displays the A record (the ip-address of the site that is queried) as shown below. In this example,

Using Emacs Macro feature you can record and play a sequence of actions inside the editor. This article explains how to perform record and play inside Emacs editor with an example. If you are a Vim editor fan, refer to our How to record and play inside Vim editor article. High Level Steps to Record and Play inside Emacs Start recording a macro by pressing ctrl+x ( Perform any actions inside the Em

Several countries provides a unique identification number (for example, social security number in the USA) to the people who live in that country. This makes it easier to identify an individual uniquely. This makes it easier to handle all the paper work necessary for an individual by various government agencies and financial institutions. Similar to the social security number, there is a concept o

Question: How do I view, modify and recreate the new initrd.img on Ubuntu, Debian, CentOS, Fedora, Red-Hat, Arch Linux, or SUSE distributions? 1. How To View Content Of initrd.img file? initrd.img is in gzip format.  So move initrd.img to initrd.gz as shown below. # cp /tftpboot/el5/initrd.img . # ls cdrom initrd.img # mv initrd.img initrd.gz Unzip the initrd.gz file as shown below. # gunzip initr

Even a Linux Geek Can’t fix the Page Not Found Issue.. Don’t worry, I promise that our Linux blog is so addictive that you might end-up eating Linux for your breakfast, Lunch and Dinner. You can do one of the following to get started. If you are visiting us for the 1st time, check-out our best of the blog page for our most popular articles on Linux and open source related technologies. Go to our h

I’ve compiled 25 performance monitoring and debugging tools that will be helpful when you are working on Linux environment. This list is not comprehensive or authoritative by any means. However this list has enough tools for you to play around and pick the one that is suitable your specific debugging and monitoring scenario. 1. SAR Using sar utility you can do two things: 1) Monitor system real ti

Linux Directory Structure (File System Structure) Explained with Examples Have you wondered why certain programs are located under /bin, or /sbin, or /usr/bin, or /usr/sbin? For example, less command is located under /usr/bin directory. Why not /bin, or /sbin, or /usr/sbin? What is the different between all these directories? In this article, let us review the Linux filesystem structures and under