Nowadays most of the Linux flavored desktop like Ubuntu, Mint, Fedora, Suse etc. are coming with very interactive user friendly graphical user interface (GUI). Using Linux GUI is similar to use other graphical user interface OS like Windows XP/7/8, Mac OS, Android or iOS etc.

Although Linux is coming with user friendly GUI but it is also providing a very strong command interface called command line interface (CLI) terminal similar to dos command interface in Windows. Similar to dos, this CLI is also not user friendly. But Linux terminal commands are important to learn as it is the base of this OS and if you learn this you can do almost anything in your system using terminal application (don’t take it so seriously, it will not cook food for you ;-) but definitely it will do).

So here is my first trick.

Use “apropos” to find your command

Any newbie when first open the Linux terminal, they can get confused because they don’t know what to do. But actually they know what to do but don’t know how to do that. So here is my first trick when you open Linux terminal. Don’t think too much, your first command is “apropos”. Using apropos command you can find all the command to do anything. For example, if you want to download a file using command, give command

apropos “download”

It will show you the list of all the commands, with their initial help, to download a file.

Now you try finding your command to download a file which is “wget”. wget command can be used as follows:

wget

But how will you know that “wget” or any other command can be used like this.

So here is my second tip.

Use “man” command for command manual page

It is very important to know about that how can you get the help of any Linux command. You can use any Linux command with care, if you will find its help. So after you know, which command can be used to do your task, check its manual page by “man” command. Linux Manual pages show the syntax and the detail description of the options of the command.

man <command>

Other than manual page of any Linux commands, a simple help is also there. So my third tip is about that.

Use “-h” or “–help” argument for command help

Most of the Linux commands have its help. Other than manual page, this help is also useful to learn the command syntax and options. Sometimes only this help is enough to execute a command but better look for its manual page to get detailed help.

wget -h

or

wget --help

Conclusion

After learning above three tips, you can find any required command and its manual or help. So, start finding and using Linux command line terminal.

Please feel free to contact me if you still need any help in using Linux.

Related Page:

Linux Commands Man Pages

These files play the important role in Linux startup and shutdown process. When a service is started through an init script, a file is touched in the /var/lock/subsys/ directory with the same name as the init script. This lock file helps in various manners like:

• This file represents that the service should be running or subsystem locked.
• It helps to avoid another instance of a service, if it accidentally started again.
• It is mandatory to create, if service need to be stopped in shutdown.

When the service is stopped, this file is removed.

However only lock file is not enough to know that the service is running or not. Status of a running service can be captured by using status function defined in /etc/rc.d/init.d/functions. Following command in an init script show the status of the service (if status case created in init script):

service <servicename> status

It checks both PID and the lock file of the service. If PID is not found but the lock file exists, you will get following message:

 dead but subsys locked

It is not always mandatory to create lock file, the services can be started and stopped without it. But it can create problem during shutdown and RUNLEVEL switch. So follow the recommended steps (recommended by me) to write a good init script (also drafting a tutorial for writing init script):

• In start section of init script touch the lock file after starting the service. You can use touch at the end of start case.

touch /var/lock/subsys/

• Don’t forget to check the lock file before starting the service in start case to avoid the multiple session of same service.

if [ ! -f /var/lock/subsys/ ]; then
     start # start service here
fi

• Don’t forget to remove the lock in stop case, it can also be added at the end of stop case.

rm -f /var/lock/subsys/<servicename>

In case system goes power down, lock files remain exist in the system due to non-execution of stop case. It does not tend it to failure as we added a check of existence of lock file in start case. , But the PID of those services will not found that means service is staled. During startup process, init checks if PID of a service exist or not. It realize a stale lock file, and clean itself up, which allow the init script to start the service successfully.

Requirement

Create a CentOS 6 bootable USB which will support customized installation (by using kickstart configuration file).

Limitations with other software

UNetbootin: Bootable USB of CentOS 6 created by UNetbootin is not even booting the system using USB and not support kickstart configuration file.

liveusb-creator: It support live Linux Fedora OS only like fedora-live and not support kickstart configuration file.

Universal-USB-Installer: It successfully boot the CentOS 6 from USB but failed to install by kickstart configuration file.

Prerequisites of ISO2USB software

This is the minimum requirement for all ISO to USB software. It need followings:

• ISO file or CD/DVD of CentOS 6 (Custom Installation disk of CentOS 6).
• A USB drive to boot the system.

Prepare CentOS 6 bootable from ISO file or CD/DVD

After downloading ISO2USB software for Windows, follow the steps given below:

• Plug the USB drive to Windows XP/Vista/7 machine.
• Execute the ISO2USB software.

ISO2USB Software

• Browse CentOS 6 ISO (with custom installation) file by using the highlighted browse button.

Browse Custom CentOS-6 ISO file

• Click on OK button but before clicking on OK button; just make sure that correct USB drive should be selected.

Select USB drive

• Click Exit button, when finished.

Exit ISO2USB

• Safely remove USB drive from Windows XP/Vista/7 system.

USB drive is now ready to install CentOS 6 (with custom configuration file) on your system.

You can use different methods to get this like using udevinfo command, from sysfs, from /var/log/messages.

Using udevinfo:

for DEV in /dev/sd*; do
udevinfo -q env -n $DEV 2>/dev/null | grep "ID_BUS=usb";
done

Using sysfs:

Change this according to your need.

find /sys/bus/usb/drivers/usb-storage/[1-9]-[0-1]:1.0/|grep -wo sd[a-z]|head -1

Using /var/log/messages:

Grep the usb device in /var/log/messages file, when usb device is connected.

I hope USB device can be detected easily now.

Windows uses FAT and NTFS as file systems, while Linux uses a variety of file systems.

Unlike Windows, Linux is bootable from a network drive.

In contrast to Windows, everything is either a file or a process in Linux. Please see one of my earlier post What “Everything Is a File” Means on Linux.

Linux has two kinds of major partitions called data partitions and swap partitions. Because of the existence of swap partitions, you never run out of memory in Linux (like in windows).

In terms of recovery tools, only a limited number of tools can be used on Windows, while there is a large number of UNIX based recovery tools available for Linux file systems.

From the author Nigel McFarlane:

Both Windows and Linux organize disk-based files into a hierarchy of directories. Such directories are usually called “folders” when viewed in a GUI. One whole hierarchy is called a “file system” on both platforms. The architecture of Windows and Linux file systems is similar in some points, but diverges greatly when tools are considered. Here’s a quick comparison.

On hardware derived from Intel or IBM PCs, both Windows and Linux use the Master Block Record/ Master Boot Record (MBR). That is the bit of disk used to boot the operating system and to state whether the disk is partitioned or not. On both Windows and Linux, it is common to have at most one file system per partition. That is about the end of the similarity.

Each Windows file system gets a drive letter, like “C:”. On Linux, each file system gets a device, like /dev/hda1 (“hard disk A part 1″), which is represented as a file. Such a file is a device file (since a disk is a device), hence the “dev” part of the path name. Also, the device file is not an ordinary text file, it is a “special file.” Since disks are block devices (unlike a serial mouse), such a file is fully described as a “block special device file.” The numbered part of the path can be a little weird to get right; it’s best to be guided by documentation there or extract the right name from a report.

On Windows, file systems can be FAT16, FAT32 or NTFS, to name a few. Recall FAT16 is the ancient standard responsible for Windows file names with the “8.3” file name length restriction. On Linux, filesystems can be “minix,” “ext,” or “ext2,” to name a few. Also, “minix” is an example of the ancient standard responsible for UNIX file names once being limited to 14 characters. Linux also has “msdos” and “vfat” file systems for compatibility with Windows and DOS, plus more.

Windows uses FORMAT.EXE to format a disk. Linux uses “mkfs” (“make file system”) in various specialist forms.

Each Windows file system has a File Allocation Table (FAT, VFAT, or similar) that states which disk blocks hold the topmost directory. On Linux, the equivalent on most filesystems is the superblock. A Linux file system has multiple copies of the superblock physically saved on the disk. This provides redundancy in case of a partial disk corruption. The superblock is just about always in memory on Linux; that is not the case for ancient DOS-like file systems. There are no special restrictions on files placed in the topmost directory on Linux, either.

On Windows, there is one drive letter per mounted file system: for example, C: for C: and D: for D:. On Linux there are no drive letters, so one file system is mounted on “/” and all other file systems are mounted on subdirectories of “/.” This arrangement is like the little-used MS-DOS command SUBST, or the NET USE command that supports Novell‘s NetWare. The equivalent Linux command is “mount.”

You can see all this at work on Linux, but for some of it you need to be logged in as root. Type “cat /etc/fstab” to see all the mountable devices, including floppy disks and CD players. Type “df” to see the devices currently mounted, and their free space. In the usual case you can even see the superblock: try “/sbin/dumpe2fs /dev/hda1” where hda1 comes from the output of “df.” The name “dumpe2fs” is a casualty of history; it replaces the older “dumpfs.” The information produced is really just for diagnostic purposes.

Mostly file systems work for you silently. If you want to dig into Linux further, then there are plenty of tools that can be used as inspection points.

About the author
Nigel McFarlane is an open source software analyst and technologist with a broad background in technology and software engineering. He has an extensive programming background and degrees in computer science and physics. His latest book is “Rapid Application Development with Mozilla” from Prentice Hall PTR.

Source:
http://searchopensource.techtarget.c…990200,00.html

• Difficulty: Easy
• Application: KStars

You may already have played with KStars, but how about creating a KStars backdrop image that’s updated every time you start up?

KStars can be run with the –dump switch, which dumps out an image from your startup settings, but doesn’t load the GUI at all. You can create a script to run this and generate a desktop image, which will change every day (or you can just use this method to generate images).

Run KStars like this:

kstars --dump --width 1024 --height 768 --filename = ~/kstarsback.png

You can add this to a script in your ~/.kde/Autostart folder to be run at startup. Find the file in Konqueror, drag it to the desktop and select ‘Set as wallpaper’ to use it as a randomly generated backdrop.

Open an SVG directly

• Difficulty: Easy
• Application: Inkscape

You can run Inkscape from a shell and immediately edit a graphic directly from a URL. Just type:

inkscape http://www.somehost.com/graphic.svg

Remember to save it as something else though!

Editing without an editor

• Difficulty: Intermediate
• Application: Various

Very long files are often hard to manipulate with a text editor. If you need to do it regularly, chances are you’ll find it much faster to use some handy command-line tools instead, like in the following examples.

To print columns eg 1 and 3 from a file file1 into file2, we can use awk:

awk '{print $1, $3}' file1 > file2

To output only characters from column 8 to column 15 of file1, we can use cut:

cut -c 8-15 file1 > file2

To replace the word word1 with the word word2 in the file file1, we can use the sed command:

sed "s/word1/word2/g" file1 > file2

This is often a quicker way to get results than even opening a text editor.

Backup selected files only

• Difficulty: Intermediate
• Application: tar

Want to use tar to backup only certain files in a directory? Then you’ll want to use the -T flag as follows. First, create a file with the file you want to backup:

cat >> /etc/backup.conf
# /etc/passwd
# /etc/shadow
# /etc/yp.conf
# /etc/sysctl.conf
EOF

Then run tar with the -T flag pointing to the file just created:

tar -cjf bck-etc-`date +%Y-%m-%d`.tar.bz2 -T /etc/backup.conf

Now you have your backup.

Read more…….

Selinux is good security feature of Linux stop you to execute malicious applications. But it need to disable when you need to run your self developed application. You can check the selinux status by using following command:

# cat /selinux/enforce

1

If it will show 1, that means selinux enforcing is enabled.

You can disable that selinux temporarily or permanently. Use following methods to disable it.

Disable Temporarily:

To disable selinux temporarily set the 0 to /selinux/enforce file.

# echo 0 > /selinux/enforce

Read more.

One of the Windows supporter write a text string (can say a command) to execute in a Linux terminal, which can crash it in just one enter.

WARNING!!!: DON’T USE THIS IN YOUR RUNNING SYSTEM, YOU CAN CRASH IT WITH JUST ONE ENTER. IF YOU DO THAT ONLY YOU WILL BE RESPONSIBLE FOR THE CONSEQUENCES.

# :(){ :|:& };:

And truly this command was doing the same, CRASHING THE LINUX IN JUST ONE ENTER.

Solution must be there, off course it is.

Read full story.

But fuser functionality is not just limited to giving information about the process. The article explains how to use fuser utility with 5 practical examples.

1. Who is Using a File or Directory?

This is the basic use of fuser command. i.e to Identify which processes are using a particular file or directory.

$ fuser  .
./:                   3965c  4175c  4281c  4334c  4337c

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