Red Hat Enterprise Linux

man command About man The man command is short for manual and provides in depth information about the requested command or allows users to search for commands related to a particular keyword. Syntax Shows you online manuals on Unix commands. man [-] [-k keywords] topic - Displays the manual without stopping. -k keywords Searches for keywords in all of the manuals available. topic Displays the manual for the topic or command typed in. Examples man mkdir Lists help information on the mkdir command. man -k irc Quickly search for manuals containing irc within them. Below is an example of what the results may look like: circle plot (3plot)  - graphics interface dircmp dircmp (1)  - directory comparison dircolors dircolors (1)  - color setup for ls ircII ircII (1)  - interface to the Internet Relay Chat system Navigation commands: 1. Space: Scroll forward one screen. 2. DnArrow: Scroll forward one line. 3. UpArrow: Scroll back o...

The internet protocol, or IP, is the protocol used to send network traffic between hosts across the internet. It comes in two versions. IPv4 is what most system administrators think of as  "IP", in which 32-bit network addresses on variable sized networks are used to address hosts. The second version, IPv6, uses 128-bit network addresses to address hosts, and provides some other changes to the protocol. IPv4 Networking Concepts IP Address: 172.17.5.3 = 10101100, 00010001, 00000101, 00000011 Netmask: 255.255.255.0.0 = 11111111, 11111111, 00000000, 00000000 An IPv4 address is a 32-bit number, normally expressed in decimal as four octets ranging in value from 0 to 255, separated by dots. The address is divided into two parts; the network part and the host part . All host on the same sabnet, which can talk to each other directly without a router, have the smae network part; the host part identifies a particular host on a subnet. In the modern internet, the size of a ...

Identify Installed Packages One of the fundamental problem in system administration is how to manage and update software installed on a system. One way to install software is simply to expand an archive of executables  libraries and other support files and copy the contents into place on the system, but it's difficult way. Many year ago, Red Hat developed the RPM Package Manager, which provides a standard way to package software for distribution, cleanly install, updates, and remove software from the system, and to ensure that all support libraries needed by an application are installed on the system properly. Once a system is installed, additional software package and updates are normally installed from a network package repository. Tools such as Packagekit and yum can be used to install individual packages or package collections (sometimes called package groups). Using PackageKit To identify what software is currently installed open the Add/Remove Software a...

Process, Priority, & Singnal concepts  A process is an instance of a running program. Processes have their own address space in memory, thread of execution, and characteristics such as security context, environment and current priority. The Linux kernel tracks every aspect of a process by its process ID number (or PID). Information about each process is advertised by the kernel to user programs through the /proc/PID directories. When a process starts another program, the new program is called its child process. Child process can have their own children, and so on. When a parent process exits all of its descendant processes also exit. Signals The Operating system communicates to processes through signals. These signals report events or error situations to processes. One typical signal is SIGTERM, which terminates the process; it asks it to exit cleanly. Another is SIGKILL, which kills the process; the process is required to exit immediately. P...

Managing User and Group in RHEL 6 To create a user in RHEL 6 we can use commands as well as graphical user administration tools. It is advisable to use  command  line as much as  possible  because it  is faster  and in real  business environment  you have to use ssh to remotely take control to administer the system. To create a user run command: useradd user_name To define a password for the user: passwd user_name Create a user with specific UID: useradd -u 802 user_name The above command will create a user with UID  802 . To create a group run command: groupadd group_name To delete a user run command: userdel user_name The above command will delete the user but it will not delete the home directory of user. To delete the home directory as well as the files contained in it run following command" userdel -r user_name User and Group Administration Given below are some sample questions about user a...

User and Group administration in redhat linux In Linux there are three type of users. 1. Super user or root user (#) Super user or the root user is the most powerful user. He is the administrator user. 2. System users System users are the users created by the softwares or applications. For example if we install Apache it will create a user apache. This kind of users are known as system users. 3. Normal users ($) Normal users are the users created by root user. They are normal users like John, Ramu etc. Only the root user has the permission to create or remove a user. In linux systems every user will have a unique user ID. It is known as UID. The Range of UIDs will be as follows: 1. Root user UID will be "0" 2. Systems users UID will be "1 - 499" 3. Normal users UID will be "500 - 60000" The range of MIN_GID and MAX_GID is specified in the file "/etc/login.defs". There are three important files a user...