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>
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
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 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.
Red hat Enterprise Linux 5 Raid Partition Part 3
Red hat Enterprise Linux 5 Raid Partition Part 2
Redhat Enterprise linux 5 Raid Partition Part 1
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.
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
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.
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.
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.
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.
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 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
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
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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