Linux Administration

cat:  Sends file contents to standard output. This is a way to list the contents of short files to the screen. It works well with piping. Syntax:  cat FILENAME. Ex: cat abc (Tells you the content of file abc). cd:  Change directory. Syntax: cd /PATH. Ex:  cd /home (Change the current working directory to /home. The '/' indicates relative to root, and no matter what directory you are in when you execute this command, the directory will be changed to "/home"). cd ..:  Move to the parent directory of the current directory. This command will make the current working directory "/home". cd ~:  Move to the user's home directory which is "/home/username". The '~' indicates the users home directory. cp:  Copy files. Syntax: cp SOURCE DESTINATION. Ex: cp abc def (This will copy a file abc to def in the same folder). cp -i abc def: (With the "-i" option, if the file "def" exists, you will be prompted befor...

In Linux the file system is based on one root directory, or hierarchical top point with subdirectories below it. In which each sub-directories has its own importance like some act as mount points, some for log messages, some for all hardware devices etc. You can find a brief description of all the directories and sub directories below: / : Its the top most directory in any of the Unix based system. /bin : Essential command binaries that need to be available in single user mode; for all users, e.g. , cat, ls, cp. / boot : Boot loader files, e.g. , kernels, initrd etc. /dev : Information of all the hardware devices. /etc : All the config files. /home : Home directories of all the users in a particular machine. /media : Mount points for removable media such as USB, CD etc. /mnt : For temporary mount points. /opt : Optional software packages like openoffice etc. /root : Home directory of root user. /sbin : System binaries like init, ip etc. /tmp : Temporary files. Ofte...

Single user mode is a mode in which a multiuser computer operating system boots into a single superuser. It is mainly used for maintenance of multi-user environments, Basically single user mode in unix based systems is known as runlevel 1. Some tasks may require exclusive access to shared resources, for example running fsck on a network share or to retrieve a lost superuser password or any maintenance task. For gaining access to #(root) prompt what you need to do is ? Once your machine is booting, for getting access to # prompt your just need to edit the bootloader i.e. in case of RHEL6 its GRUB (GRand Unified Bootloader).  Once your machine is booting just press a key couple of time so that you are brought to the GRUB menu. The GRUB menu appears like the image shown below: The values which are show in this window are the kernerl(s) which are installed in your machine. Use the cursor keys to switch between kernels (if you have mo...

RHEL6 installation is very simple you just need to do some clicks and few selections and your operating system is ready. Assuming you have a RHEL6 disk and a system in which you can install RHEL6. Boot your machine and select the boot device a DVD. You will see a screen like the given below: Select the installation type as "Install system with basic video driver". If your disk is a new one then you can skip this check otherwise do check your disk for any errors. Here I did skip this step, as I was aware that this will not give any issues while installing the machine. After this you will see a screen somewhat like this, Just press Next. Choose a language as per your requirements. Choose the keyboard layout as per your requirements. Select the storage device in which you want to install your OS. Type the hostname of your machine(as per your requirements). Select the time-zone. Give root password for ...

Linux is an operating system which was assembled under the model of free and open source software development and distribution. The main component of Linux is the Linux kernel, The first release of this Linux was done by Linus Torvalds in Oct 1991. It was originally developed as a free operating system for Intel x86-based personal computers but now it supports nearly all the computer hardware's. Mainly it is used on servers, mainframes, supercomputers but now a days it is being heavily used in mobile devices some of the examples are Maemo, MeeGo, Android etc. The development of Linux is one of the most prominent examples of free and open source software collaboration: the underlying source code may be used, modified, and distributed—commercially or non-commercially—by anyone under licenses such as the GNU General Public License. Some of the Linux flavors are: RHEL: Red Hat Enterprise Linux. Suse. Fedora. Mandriva. Debian. Ubuntu.... and many more. A Linux-based s...

If by any chance you are appearing for an interview for a position if Linux Administrator then the most common question which is asked is what is the difference between RHEL5 and RHEL6 ? Virtualization: In RHEL 6 KVM (Kernel based Virtual Machine) was used as a hypervisor but in the earlier releases of RHEL XEN was used as a hypervisor. The main advantage of KVM is that it supports the installation of many virtual machines/operating systems like Windows, Linux, Solaris and also it is very easy to manage those virtual machines. Security: RHEL6 has an enhanced version of SELinux(Security Enhanced Linux) now, Basically now the features are more improved and there are various new set of rules which are added to SELinux one of such rule/feature is of SVirt which provides security to virtual machines from hackers. EXT4: It stands for Extended 4, It has various new advantages then EXT2/3 which were used in earlier version(s) of RHEL. EXT4 is comparatively more faster and easy t...

RHEL stands for Red Hat Enterprise Linux, the current version of RHEL which is running successfully in Market is RHEL6. RHELis basically based on subscription basis where if you are a subscribed user then you will be benefited and can access all the supported versions of the operating system in binary as well as source form. Its first release was RHEL2.1 which was released in 2002. The major version of RHEL are released mostly in about 2-3 years but the minor ones are released nearly after every six months. Currently RHEL comes for: Servers. Desktops. If you are a subscribed user then you can get full support from Red Hat, you can access there knowledge base which you can access and can resolve your issue yourself and if by any chance you are unable to do that then you can always contact to Red Hat's Technical Support team for your queries.