REDHAT certifications

Journaling

Journaling avoids the time-consuming check that is automatically performed on a filesystem when it is abruptly unmounted for instance, as a consequence of a system crash.

System Calls

             Operating systems offer processes running in User Mode a set of interfaces to interact with hardware devices such as the CPU, disks,and printers. Putting an extra layer between the application and the hardware has several advantages. First, it makes programming easier by freeing users from studying low-level programming characteristics of hardware devices. Second, it greatly increases system security, because the kernel can check the accuracy of the request at the interface level before attempting to satisfy it. Last but not least, these interfaces make programs more portable, because they can be compiled and executed correctly on every kernel that offers the same set of interfaces. Unix systems implement most interfaces between User Mode processes and hardware devices by means of system calls issued to the kernel.

Network Commands

• ssh – SSH client (remote login program)                                    :

“ssh is a program for logging into a remote machine and for        
   executing commands on a remote machine”
Usage: ssh [options] [user]@hostname 
eg. ssh ­X guest@10.105.11.20        

                         
• scp – secure copy (remote file copy program) :
                          
“scp copies files between hosts on a network”
Usage: scp [options] [[user]@host1:file1] [[user]@host2:file2]
eg. scp file1.txt guest@10.105.11.20:~/Desktop/

What does Linux mean?

Linux is a free and open source Unix-like computer operating system originally developed for Intel x86-based personal computers by Linus Torvalds. The name Linux is used in many ways ie as a kernel, as an operating system as GNU/Linux (because so many of the Linux programs and commands come from the GNU project), the term Linux is also used for a Linux distribution. During the development Linux Torvalds stored the files to the FTP server (ftp.funet.fi) of Finnish University and Research Network (FUNET) under the name “Freax” ( a portmanteau of “freak”, “free”, and “x” for UniX). One of the administrators for the FTP server at the time, did not think that “Freax” was a good name. So, he renamed the project name to “Linux” (as a a portmanteau of Linus Torvalds and Unix) on the server.

Basic UNIX Commands

init 0,1,2,3,4,5,6 - running modes of an Unix operating system (Solaris)
hostname - Get Hostname
date - Get date and time
cp - copy
ls - list contents in directory
cd - change directory
cd .. - back sirectory
cd \ - change to root directory
mv - move contents
history - show history of commands we used.
grep - to search pattern from a command output
date - to show date
wget <URL> - to download a particular entity from that web location.
gzip - to compress a file
tar - to zip a folder or combination of files
man <command> - to show detailed info of pages
find <location> -name <filename/pattern> - To search a file from that desired location.

UNIX OS Flavours

The following is some of the well-known Unix flavors, with links to their official home pages.

AIX - IBM
BSD/OS (BSDi) - Wind River
CLIX - Intergraph Corp.
Debian GNU/Linux - Software in the Public Interest, Inc.
Tru64 Unix (formerly Digital Unix) -  Compaq Computer Corp.
DYNIX/ptx - IBM (formerly by Sequent Computer Systems)
Esix Unix - Esix Systems
FreeBSD - FreeBSD Group
GNU Herd - GNU Organization
HAL SPARC64/OS - HAL Computer Systems, Inc.
HP-UX - Hewlett-Packard Company
Irix - Silicon Graphics, Inc.
Linux - several groups several
LynxOS - Lynx Real-Time Systems, Inc.
MacOS X Server - Apple Computer, Inc.
NetBSD - NetBSD Group
NonStop-UX -  Compaq Computer Corporation
OpenBSD -  OpenBSD Group
OpenLinux -  Caldera Systems, Inc.
Openstep - Apple Computer, Inc.
Red Hat Linux - Red Hat Software, Inc.
Reliant Unix - Siemens AG
SCO Unix - The Santa Cruz Operation Inc.
Solaris - Sun Microsystems (now ORACLE)
SuSE - S.u.S.E., Inc.
UNICOS - Silicon Graphics, Inc.
UTS - UTS Global, LLC