What you need to know before installing RHEL

Ii. How to control hardware in Linux

1. kernel is responsible for controlling hardware devices.
Kernel can control most of the main hardware devices in a Host:
CPU and memory.
The kernel also has the function of dynamically loading the driver:
If there is a newer or frequently-needed hardware device in this host, or the hardware device can support some additional features of the source, such: some firewalls have the kernel level encapsulation function to dynamically load the drivers of these hardware devices into the kernel so that the kernel can control these hardware devices.
2. You can use User Mode Access to access the kernel. User Mode access includes the following three parts:
· System calland Singnals
This is a development interface, similar to an API;
· Device nodes
(Hardware files) that is, the files corresponding to hardware devices in the file system are used to access the kernel;
· Network Interface
That is, the control mode of the network interface. The network interface is not controlled by the device nodes in the file system, but by the network interface;

Iii. Introduce hosts and CPU and memory supported by RHEL

1. RHEL supports the following seven types of hosts: Intel (x86, Itanium2), amd64/em64t, IBM (S/390 large host, zsseies large host) iseries (IBM as400 host), pseries (IBM unix host is rs6000 host)
2. CPU usage on the x86 host
· If RHEL as is installed, more than two CPUs are supported, the two CPUs can use hyper-threading at the same time (that is, the technology of simulating one CPU with two CPUs );
· If SMP is used (that is, the kernel supporting multi-processor architecture) or hugemem kernel is used, the 32-particle CPU can be supported;
3. memory on the x86 host
· If RHEL's as or ws version is installed, 16 GB of memory is supported;
· If the general i686 or athlon kernel is used, only 4 GB of memory is supported;
· If SMP, i686, or athlon kernel is used, 16 GB of memory is supported;
· If hugemem SMP's kernel is used, 64 GB memory is supported;

4. Introduction to preparations before installation

1. Before installing RHEL, you 'd better check the release announcement file first, these files can be found on the first disc of the installation disc (the HTML file starting with release-notes on the disc is of course included in many language versions) and can also be found in the http://www.redhat.com

These files are found on the website.
2. Check whether your hardware device is compatible with RHEL.
· On the RedHat website, you can find a hardware list that supports RedHat Linux. The list can be divided into two types:
One is a RedHat-certified hardware device, and the other is a hardware list compatible with RedHat Linux.
· The display card must support xfree86 and can be in the http://xorg.freedesktop.org

Find information about the display card;

V. Introduction to multiple boot Systems

1. Grub will be used as a preset during RHEL installation.
Bootloader boot Management Program. Grub allows RHEL and the following systems to be installed on one host simultaneously, including Windows NT/2000/XP/2003
, DOS, Windows 3.x/ 9x/Me, NetBSD, FreeBSD, and other systems;
2. Two problems may occur when multiple boot systems are installed.
· Solution to the first partition: when installing RHEL, you must divide some Linux partitions so that RHEL can store data, therefore, if multiple boot systems are required, we recommend installing other systems before installing RHEL, when installing other systems, you must leave some unpartitioned space on the hard disk as Linux partitions;
· Method 2: to enable a multi-boot host, you must install bootloader to enable all the operating systems on the host to start up:

6. Introduce device node (which files will the hardware device correspond to in the system)

Device nodes can be divided into three categories:
1. Block devices
·/Dev/hda
These files correspond to the hard disk of the IDE interface in the system. A indicates the number of the IDE hard disk, and the first partition corresponds to a number. For example:
 
·/Dev/SDA
These files correspond to the hard disks of the SCSI or SATA interface in the system. Here, A is also the hard disk number, followed by a number to indicate the partition;
·/Dev/fd0
These files correspond to the floppy disk in the system. 0 indicates the number of the floppy disk;
2. Character Devices
·/Dev/tty [0-6]
These files correspond to the virtual consoles in the system)
·/Dev/st0
These files correspond to the SCSI tape drive in the system;
Next we will compare the differences between Block devices and character devices.

	Block devices	Character Devices
Data access unit	· Block as the access unit (512 or 1024 bytes) · Access a block of data at a time	· Use character (character) as the access unit (1 byte) · One character data is accessed at a time
Features	· Fast access · Random Access	· Slow access speed · Sequential access is required
View The attributes of an archive can be used to determine which archive is used.	B Rwxr-XR --	C Rwxr-XR --
Example	Hard Disk belongs to this archive type/dev/hda1	Tty [0-6] the virtual console belongs to this type.

3. Symbolic Links
This type indicates the link file, which is the same as the shortcut function in Windows. The first character of the file attribute is L (lower case l). For example:L

Rwxrwxrwx

7. Introduce some RHEL Installation Tools

There are two phases for installing RHEL
1. In the first phase, you must have an image file that can be turned on to start the computer. You can start the computer in the following three ways:
· Diskboot. img
 

The first method is to use the diskboot. IMG file. diskboot. IMG is a vfat file system image file, which stores many files that must be used for boot,
This file is usually stored in a USB flash drive and boot with a USB flash drive. However, you must pay attention to whether the BIOS of the host supports USB Flash boot. The diskboot. imgfile is usually larger than the file in the boot floppy disk.
Some.
Note: boot from a floppy disk is not supported in RHEL4.
· Boot. ISO
The second method is to use the boot. ISO file. boot. ISO is an image file of the iso9660 File System (that is, the file system used by the CD), that is, boot with the CD.
· Pxeboot directory
The third method is to use the pxeboot directory, PXE (P
Re-boot ex
Ecution E
Environment ronment), this method is used in a large number of installation, you can refer to the/usr/share/doc/syslinux-2.11/pxelinux.doc (note: this file in English) this file to deploy the pxeboot directory.
2. Install RHEL in the second phase.
· You can manually install RHEL on the graphic interface or text interface;
· You can also use the noprobe installation mode or kickstart automatic installation mode to install RHEL;

8. Introduce RHEL installation features

1. You can use the noprobe installation mode and the Kickstart automatic installation mode;
2. If you use a CD-ROM for installation, you can test the CD-Rom before installation to avoid problems during installation;
3. You can install RHEL in either of the following ways:
· Graphical interface

When RHEL is installed on the GUI, X server is started and RHEL is installed on the GUI;
A graphical interface can be used only when RHEL is installed using image files on hard disks, CDs, and NFS;
A graphical interface is a preset installation interface;
· Text interface

The text interface displays all interfaces on the screen in the form of a menu, such as the text installation interface:

 
All installation methods can be installed in text mode.

9. Introduce the RHEL installation process (eight steps in total)

1. Select the language, keyboard, and mouse types used for installation;
2. Select the media in which the RHEL file is stored;
3. Partition the disk;
4. Set the Bootloader and boot the management program;
5. Set the NIC and firewall values, such as the IP address of the NIC;
6. Set the root password;
7. Select the tools required for installation of the software package;
8. set X Server

10. Introduction to disk partitioning

1. When a new hard disk is obtained, partitioning is preferred;
2. format the partition into the file system format;
·
Partition can be divided into: Primary (primary partition, can be divided into up to 4), extended (extended partition, if the four primary partitions are not enough, one of the primary partitions can be divided into one extended partition) and logical (logical partitions can only be divided into extended partitions and multiple partitions can be divided );
·
In RHEL4, the default file system is ext3;
·
We can use soft RAID or LVM technology to aggregate Several partitions into several large virtual partitions;
3. After a partition is formatted as a file system, you must mount the partition to a mount point (that is, a directory) to access the partition, A mount point is a directory in the hierarchical architecture of the file system. You can store data in a partition using this directory;

11. partition structure in Linux

1. An example of a disk partition:

2. If you enlarge the MBR, you can split it into three parts.
· Boot Loader
The size of boot loader is fixed to 446 bytes, which stores the required information during boot. The main function of this information is to select the partition from which the boot loader is loaded into the operating system, if the grub boot management program is installed, the code of the first stage of grub will be stored here;
· Partition talbe
This
The size of the part is fixed to 64 bytes. Here, the disk space required to record the start and end of each partition is fixed to 16 bytes, therefore, the most
You can only divide four partitions. If you divide one partition into multiple partitions, the partition table cannot be used because there is no extra space in the MBR to store 5th partitions, if you need to use four
In the preceding partitions, three primary partitions and one extended partition can be used. As shown in the partition structure, extended partitions cannot be used directly, logical partitions must be divided into extended partitions to be sufficient.
In the extended partition, links are used to record the magnetic column corresponding to each logical partition, indicates the start and end magnetic column of the extended partition in the MBR.
The first magnetic area of a logical partition also records the position of the starting and ending magnetic column, and records the starting and ending magnetic column of the next logical partition. The following logical partitions are the same as above, this forms a chain.
Connection method );
Although the first magnetic zone is retained in the four magnetic zones recorded by MBR, no information is recorded in these magnetic zones;
· Magic
The size of this part is fixed to 2 bytes, And the magic num of each BIOS is stored in magic;

12. Notes for setting up an archive system

1. When installing RHEL, the installer requires partitioning. After partitioning, the installer will format these partitions (you can see the legend of partitioning in the section "demonstrate RHEL installation );
· When partitioning, you must specify a mount point for these partitions, set the size of each partition, and format the file system;
· You can select to enable the installation to automatically partition and format the partitions, or manually divide the partitions by yourself;
2. When partitioning, you can refer to the following settings:
· The/etc,/lib,/bin,/sbin, And/dev directories must be in the same partition as the root directory;
· The partition where SWAp is located is usually twice the actual memory size;
· Use the following directories as Mount Points;
/Boot. All the files required for starting the system will be stored in this directory by default to facilitate future backup and restoration;
/Home: This is a directory for storing all users' personal files, facilitating future backup and restoration work and disk quotas;
/Usr. All commands and kits of RHEL are stored here under Preset conditions to facilitate future backup and restoration;
/Var: stores all changeable information, such as log files and emails not read by users; this directory can be used as a mount point to determine whether backup or disk quota is required for this directory;
/Tmp, which allows all users to store temporary archives. As a mount point, this directory can be used to determine whether backup or disk quota is required;
/Usr/local,/OPT, except for the commands and kits of RHEL itself, the kits of all other manufacturers will be stored in these two directories for future backup and restoration work;

13. Introduction to software raid)

1,Raid disk array
(R

EdundantA

RrayI

NexpensiveD

Isks)
· We can combine different partitions in multiple hard disks and convert these partitions into a RAID device through the features of the software;
· The raid directory is used to provide Fault Tolerance solutions for the data stored in the hard disk, or to combine multiple hard disks into an array. Raid can also increase the efficiency of hard disk access;
· Linux also supports hardware raid, but it must use some special hard disk control devices, such as raid cards, to allow Linux to recognize multiple partitions as one RAID device;
2. When installing raid, you can select the following RAID levels:
· RAID 0:
· RAID 1:
· RAID 5:
Comparison of the three levels is as follows:

	RAID 0	Raid 1	RAID 5
Number of hard disks or partitions required	2	2	3 # It is the logical operation value of the data in the other two disks, which is used for fault tolerance.
Features	· Fast access · No Fault Tolerance	· Fault Tolerance · Slow access speed	· Safer than raid0 · The access speed is not necessarily faster than raid1, because it also requires calculation and storage of logical values.
Available capacity	Total capacity of all hard disks or partitions	Half of total capacity	Total capacity of three hard disks or partitions minus capacity of one hard disk or partition
Recoverable data?	Damaged parts cannot be recovered	Damaged parts can be recovered	Damaged parts can be recovered Two damaged parts cannot be recovered.

3. You can perform software raid during the installation process, for example:



If you want to set RAID 0, at least two raid partitions must be created and the sizes must be the same. Then, click the raid button to merge the two partitions into one raid partition.

By creating a raid, Note: If the created mount point is a boot partition (for example, the root directory/AND/BOOT), only the raid level can be used,

 

14. Introduction to LVM logical magnetic zone Administrator (logical volume manager)

1. LVM is developed from IBM's aix unix system;
LVM concept:
Partitions are first separated from one or more hard disks. these partitions are calledPV
(P
Hysical v
Olume), and thenPV
AddVG
(V
Olume g
Roup), when severalPV
After a VG is combined, LVM will perform similar formatting on all PVs and cut each PV into blocks. The space of these blocks is calledPE
(P
Hysical E
Xtent), you can setVG
Imagine a virtual hard disk,VG
It cannot be used directly.LV
(L
Ogical v
Olume)LV
Storing data,LV
Not necessarily correspondPV
For example, the magnetic zone of LV1 may be scattered in threePV
In this example, when LV1 is not enoughVG
In the other unused magnetic areas, a logical magnetic area is drawn and added to LV1, which does not affect the data originally stored in LV1, that is, the effect of the dynamically enlarged magnetic area:
 
2. Create LVM as an example:
During RHEL installation, you can perform LVM processing on the disk during disk partitioning.
When creating a partition, select physical volume (LVM) as the file system type, set the size to 1000 MB, and create two PVS.
 
After setting up two PVS, click the LVM button, for example:

Here, the LV size can be modified, but there may be files in the original magnetic area. It is not recommended that the size of the magnetic area be smaller.

15. Network Settings

1. During RHEL installation, the network settings page can be set on each Nic separately. These settings include the following:
· Automatically obtain or manually set through DHCP;
· You can also set the NIC to take effect when it is enabled;
For more information, see the following figure.

16. Introduction to firewall settings

1. The role of the firewall is to restrict remote users to access resources on the host;
2. During RHEL installation, you can select Enabled or no firewall on the firewall settings page );
3. Some specific services may be opened if the firewall is enabled, indicating that remote users can connect to the host and access these specific services;
For the legend, see the legend set by the firewall in the "RHEL installation" section.
·
By default, the firewall is enabled and we are required to set which services are enabled. If the firewall is not enabled, all unknown connections are blocked. If you select these services, then the Firewall
The ports used by these services are enabled, and remote users or ports used by these services connect to this host, they can access resources on this host through firewall restrictions.
For example, if this host has Web Services, you must check the Web Server service options.

17. Introduction to SELinux (security enhanced Linux)

1. SELinux enables us to set more detailed access control on each object, that is, to allow which process handlers and which objects can be accessed;
· In traditional Linux, access permissions are not set for each object. That is to say, the owner of each object must set the permissions on the object.
· If SELinux is enabled, you can use SELinux to manage more detailed access permissions for all objects in the system;
2. When installing RHEL, the installer provides some SELinux options:
·Disabled
Disable SELinux
·Warm
If this option is selected, a warning message is received when access is denied, but security rules are not applied;
·Active
This is a preset option. SELinux is enabled and all security rules are applied;

18. How to select the suite to be installed

1. Software Package Selection
· If the disk space is sufficient, you can choose everything to install all the suites;
· You can also install only the preset kit, and the preset package list is stored in the RedHat/base/comps. xml file of the disc;
· The custom installation kit, as shown in the previous section, demonstrates that when RHEL is installed, the suite is selected to customize the suite to be installed;
For more information about how to install RHEL, see the following section.

19. describes how to confirm that Linux has been installed

After RHEL is installed, the system requires that the computer be restarted. After the computer is restarted, the system searches for hardware devices on the host and displays information about these hardware devices on the screen, you can also view the information in the following ways:
1. dmesg can use this command to view system information;
2./var/log/dmesg view the system information by viewing the file;
3. When an error occurs in the system,/var/log/messages records all error information in this file;
4. The/root/install. Log installer records all information during the installation process to this file;

20. Introduce noprobe mode and driver disks mode during installation

1. When there are newer hardware devices in the environment that may make the installer unable to identify the device, you can use noprobe and driver disks to install RHEL;
2. If RHEL is installed in these two modes, hardware devices in the system will not be detected before installation, and hardware information will be provided by users;
3. When the following conditions occur, the system requires the user to provide the driver for the hardware device:
· When RHEL is installed in noprobe mode, the system requires us to provide the driver;
After starting the computer with the system CD, enter the noprobe command after boot: to enter this mode.
· When you use the Linux dd command to install RHEL in driver disks mode, the system will require us to provide the driver disk;
After starting the computer with the system CD, enter the Linux dd command after boot: to enter this mode.
· When no PCI device is detected during installation, the system also requires us to provide the driver;

21. Introduce the setting after installation is complete.

1. If you use a graphical interface to install RHEL, the setting proxy program will be started at the first startup, which will guide us through the following options, detailed configuration steps have been introduced in the previous section. Here is a summary:
· Display settings;
· Set the date and time;
· Ask if other kits need to be installed from the CD;
· Create other user accounts;
· If you have a sound card, we will be prompted to test the sound card;
· Requires that you complete the registration process with RedHat to download the update files and other suites;
2. You can also enterSystem-config-name to be set
You can enable the graphical interface setting tool;
For example, system-config-Display Settings
System-config-network Nic settings
System-config-Date: set the date
 

 

Reference

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