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How to Configure the Runlevels In Redhat Enterprise linux

To configuring which services are started for a runlevel, use one of three programs: chkconfig (command line only), ntsysv (simple text-based application that doesn’t require a graphical desktop), or the Service Configuration Tool (graphical application).
The chkconfig command can be used to configure runlevels and list the current runlevel configuration. It must be run as root if modifying a runlevel. Otherwise commands such as listing whether a service is started at boot time can be run as a non-root user.
To list the status of all services, execute the chkconfig --list command. A line is output for each service such as the following for the Apache HTTP Server:

How to Runlevels in RHEL

How does the system know which initialization scripts to run so that only the desired services are started at boot time? Linux uses the concept of runlevels to define which services to start at boot time. There are 7 runlevels, with each having its own general purpose:
 0: Halt the system or Shutdown
 1: Single-user mode (For system recovery & restore mode)
 2: Not used
 3: Multi-user mode with text login
 4: Not used
 5: Multi-user mode with graphical login
 6: Reboot

How to Initialization Scripts in RHEL

Network services such as the Apache HTTP Server and DHCP along with other programs such as cron and syslog require a daemon to be running at all times. The daemon performs actions such as listening for connections to a service on specific ports, making sure commands are executed at specific times, and capturing data such as log messages when they are sent out by other programs.Programs that require a

File Permissions in Linux

In Red Hat Enterprise Linux, all files have file permissions that determine whether a user is allowed to read, write, or execute them. When you issue the command ls -l, the first column of information contains these file permissions. Within this first column are places for 10 letters or hyphens. The first space is either a hyphen, the letter d, or the letter l. A hyphen means it is a file. If it is the letter d, the file is actually a directory. If it is the letter l, it is a symbolic link to a directory somewhere else on the file system. The next nine spaces are divided into three sets of three. The first set of three is the read, write, and execute permissions for the owner of the file. The second set of three is the read, write, and execute permissions for anyone who belongs to the user group for the file. The last set of permissions is for anyone who has a login to the system.


As you might imagine, the differences between Microsoft Windows and the Linux operating system cannot be completely discussed in the confines of this section. Throughout this topic, we’ll examine the specific contrasts between the two systems.But before we attack the details, let’s take a moment to discuss the primary architectural differences between the two operating systems.
Single Users vs. Multiple Users vs. Network Users
Windows was designed according to the “one computer, one desk, one user” vision of Microsoft’s cofounder Bill Gates. For the sake of discussion, we’ll call this philosophy single-user. In this arrangement, two people cannot work in parallel running (for example) Microsoft Word on the same machine at the same time. (On the other hand, one might question the wisdom of doing this with an overwhelmingly weighty program like Word!) You can buy Windows and run what is known as Terminal Server, but this requires huge computing power and extra costs in licensing. Of course, with Linux, you don’t run into the cost problem, and Linux will run fairly well on just about any hardware.
Linux borrows its philosophy from UNIX. When UNIX was originally developed at Bell Labs in the early 1970s, it existed on a PDP-7 computer that needed to be shared by an entire department. It required a design that allowed for multiple users to log into the central machine at the same time. Various people could be editing documents, compiling programs, and doing other work at the exact same time. The operating system on the central machine took care of the “sharing” details so that each user seemed to have an individual system. This multiuser tradition continues through today on other versions of UNIX as well. And since Linux’s birth in the early 1990s, it has supported the multiuser arrangement.

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