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RedhatEnterpriseLinux Blog
How to Removing Software /RPM
To remove a package, issue the following
command:
rpm -e
<packagename>
Notice that this time, only <packagename> is used, not the full name of the file used to
install the software. When this command is issued, the RPM database is searched
for the files associated with this package, and they are removed.
If multiple versions of a package are
installed, such as the kernel, the package version can also be specified to
make sure the correct version is removed:
rpm -e
<packagename>-<version>-<release>
How to Updating Software/ RPM
If an RPM package is already installed, it can
be updated to a newer version. With RPM, there isn’t the concept of using a
different file or set of files to perform a software upgrade. The same RPM file
or files used to install a program can be used to update the program as well.
To update to a newer version of a package
already installed:
rpm -Uvh
<packagename>-<version>-<release>.<arch>.rpm
How to Install a New Kernel RPM
There is a -i
argument to RPM to install packages,
but it is more convenient to use –U
when installing and upgrading software
because -U installs or upgrades the package depending on
whether or not it is already installed. However, there is an exception: installing
a new kernel. When installing a new kernel, you should keep the current kernel installed
in case the new kernel does not work with the system’s hardware, does not
perform as well as the current kernel, or causes other problems. When you use
the –U argument
to RPM, the older version of the software package is no longer available.
Installing RPM Package Software
Installing
an RPM package can be done via the command line or a graphical program. Because
some systems such as servers do not always have a graphical desktop installed,
it is important to learn at least the basics of how to use the command-line
version of RPM. The command is simple to remember: It is the rpm
command.
Before
installing any software, confirm that it was packaged by a trusted source and
has not been altered since the trusted source built it. This process is done by
checking the GPG signature of the package.
Understanding How RPM Works
How does RPM work? Each software program consists of files and
directories, most of which must be located in a particular place on the
filesystem. If the software program is distributed in RPM format, these files
are compressed together into one RPM file along with instructions on where the
files should be located on the filesystem and any additional scripts or
executables that must be run before or after the files are installed. These RPM
files are often referred to as packages.
A software program, such as the Firefox web browser, might consist
of one RPM file. However, some programs are divided into multiple RPM files to
allow the administrator to customize which parts are necessary for the system’s
usage. For example, the GNOME graphical desktop is divided into many packages
that contain parts of the overall desktop.
How to Finds File in linux
There are two invaluable commands that can be
used to find files on the filesystem: locate
and find. The locate command
is the easier of the two to use. Just type the command followed by part or all
of the filename you are searching for such as locate .odt to find all
OpenOffice.org text files or locate
compare to find all
filenames that contain the word compare. Notice that no wildcard
characters are used. It is assumed that what you type may only be part of the
filename you are looking for.
The only catch to this command is that it
relies on the generation of a database file so it can quickly display results.
The locate command is provided by the mlocate
package, which also provides the cron
script /etc/cron.daily/mlocate.cron to
How to Find Commands
If you know a command exists on the system but keep getting the
error message command not found, check to make sure you are typing the command correctly.
Otherwise, it might not be in your PATH environment variable. To view the value of your PATH, execute the command echo $PATH from the command line. As you can see, your PATH
is a list of directories. When you execute a
command without providing its full path, it must be in one of the directories
listed in your PATH. Otherwise,
the command not found error is displayed. You
can provide the full path to the command if you know it, such as /sbin/lspci
to execute the command to list the PCI
devices. If you use the command often, but it is not in your PATH, you can add the directory to your PATH.
How to Read Text Files in linux
Sometimes you want to quickly read a text file such as a
configuration file without having to open a text editor. This is possible with
the less, more, and cat command-line
utilities. All three have the same basic syntax but work differently and have
different commandline options. To use them in their default modes, type the
command followed by the text file to read such as less
output.txt, more /var/loasg/messages, or cat
/etc/sysconfig/ network.
How to Become the Root User
It is important to log in with your user account instead of as the
root user when performing day-to- day tasks. Some of the graphical
administration tools will prompt you for the root password if you try to run
them as a regular user. But, what if you are logged in as a user and need to
perform an operation only the root user can do? It would be time consuming to
close all your open windows, log out of the graphical desktop, log back in as
root, execute root-only commands, log out again, and then log back in with your
user account.
How to Configure Service Configuration Tool
To immediately start, stop, or restart a service, select it from
the list and click the Start, Stop, or Restart button. This does not affect whether it is started or stopped at
boot time. If you do not have the graphical desktop installed or just prefer a
more simplistic interface, ntsysv can be used to configure runlevels. The program must be run as the
root user.
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.
DIFFERENCES BETWEEN WINDOWS AND LINUX
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.
CentOS 6 Installation step by step
How to install Linux – Centos 6
Set your computers BIOS to boot form CD / DVD
- Insert the CentOS 6 CD or DVD
- When
presented with the following screen press enter on Install or
upgrade an existing system.
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