RH133 redhat enterprise linux system administration

 Primary, extended and logical partitions  The default filesystem is ext3  Multiple partitions may be assembled into a larger virtual partitions: software RAID and LVM  Filesystems

Redhat Enterprise Linux System

Administration

Unit 1

 Installation

Hardware Overview

 Kernel Support

 Core support: CPU, Memory, Process

 Management , Interrupt/Exception Handling etc.

 Dynamically Loadable Kernel Modules

 Device Drivers

 Additional Functionality

 User Mode Access to kernel facilities

 System Calls and Signals

 Filesystem Device Nodes

 Network Interfaces

CPU and Memory

 Seven Supported Architectures: x86, Itanium2,

AMD64/EM64T, S/390, zSeries, iSeries, pSeries.

 CPU Support on x86

 Technical support for more than 2 physical CPUs only on

AS variant (may use Hyper-Threading)

 Up to 32 Physical CPUs with SMP or hugemem kernel.

 Memory support on x86

 Technical support for more than 16 GB on AS or WS

 Standard i686/athlon kernel: 4GB

 SMP i686/athlon kernel: 16GB

 Hugemem SMP kernel: 64GB

Preparing to Install

 Read the RELEASE-NOTES file on the first

CD or at http://www.redhat.com

 Check Hardware Compatibility

 Redhat Supported Hardware List

 Hardware compatible with Redhat Linux

 http://hardware.redhat.com/hcl

 XFree86 supported video cards.

 http://xorg.freedesktop.org

http://www.x.org/wiki

Multiboot systems

 Redhat Enterprise Linux and the GRUB boot

loader can co-exist with other operating systems, including the following:

 Windows NT/2000/XP/2003

 DOS, Windows 3.x/9x/ME

 NetBSD, FreeBSD and other open systems.

 Two major issues arise when implementing

multiboot systems:

 Partitioning and the boot process.

 A boot loader such as System Commander or

NTLDR is already on the system and will launch

GRUB as a secondary boot loader.

Device Node Examples

 Block devices:

 hd[a-t] IDE devices

 sd[a-z]+ SCSI devices

 fd[0-7] Standard floppy drives

 md[0-31] software RAID metadisks

 loop[0-15] loopback devices

 ram[0-9] ramdisks

 Character Devices:

 tty[0-31] virtual consoles

 ttyS[0-9]+ Serial ports

 lp[0-3] Parallel Ports

 null infinite sink ( the bit bucket)

 zero infinite source of zeros

 [u]random sources of random information

 fb[0-31] framebuffer devices

 Symbolic Links:

/dev/cdrom - - > /dev/hd[a-t], /dev/sd[a-z]+

The RHEL Installer

 First Stage Installer Images

 diskboot.img – VFAT filesystem image for

bootable media larger than a floppy

 You will need to use the dd command to move this image to you media For

instance:

dd <diskboot.img > /dev/sda

 Floppy installation is no longer supported

 boot.iso ISO9660 bootable CD image

 Booting form boot.iso is the same as passing the askmethod argument to the installer when booting from CD 1.

 You can create a bootable CD using the cdrecord command For instance

cdrecord dev=/dec/hdc boot.iso

Installer Features

 noprobe and Kickstart modes available

 mediacheck tests media integrity

 Multiple Interfaces:

 Graphical

 Starts X server and a GUI installer

 Can be started in lowers mode.

 Works with hard drive, CDROM, NFS Installation

 Graphical is the default

 Text

Menu-based terminal interface

RHEL Installation Overview

 Language, Keyboard and mouse selection

 Media selection if applicable

Partitioning Hard Drives

 Hard drives are divided into partitions

 Partitions normally contain file systems

 Primary, extended and logical partitions

 The default filesystem is ext3

 Multiple partitions may be assembled into a larger virtual partitions: software RAID and

LVM

 Filesystems are accessed via a mount

point, which is a designed directory in the

Software RAID

 Redundant Array of Inexpensive Disks

 Multiple partitions on different disks combined into one RAID device

 Fault tolerance, larger disk size, performance

 Install-time RAID levels:

 RAID 0: Striping (no redundancy)

 RAID 1: Mirroring

 RAID 5: Striping with distributed parity

Configuring File Systems

 Must select mount points, partition sizes, and file system types in the installer

 Can set up manually or automatically

 There are many layouts which may be

used

 / mast include /etc, /lib, /bin, /sbin, /dev

 Swap space is typically 2x physical RAM

 Typical mount points: /boot, /home, /usr, /var, /tmp, /usr/local, /opt

LVM: Logical Volume Manager

 Manages storage on one or more

partitions as virtual partitions, or logical volumes

 Real partitions are physical volumes and are assigned to a volume group (a virtual disk)

 Disk space in the volume group is divided into extends which are assigned to a logical volume

 Easy to resize logical volumes

 Add a physical volume to the volume group

and assign the new extents to the logical

 “Trusted Devices” can bypass the firewall

 Can allow access to arbitrary services

Security Enhanced Linux

 Access control determines what actions

processes can perform on what objects

 Discretionary Access Control (Traditional Linux)

 Users control permissions on objects

 Mandatory Access Control (SELinux)

 System policy restricts permission which can be granted.

SELinux Installation Options

noprobe Mode and Driver Disks

 Method for supporting hardware newer than the install program

 Used at install time for less common

hardware

 Prompt for Driver Disk

 When run in noprobe mode

 When started with: linux dd

 When no PCI devices are detected.

Post-Install Configuration

 Setup Agent (firstboot)

 Configure X window System if necessary

 Set date and time

 Register with Redhat Network and get updated RPMs

 Install additional RPMs or Redhat

Documentation from CDROM

 Setup users

 system-config-* configuration tools

Unit 2

 System Initialization and Services

Boot Sequence Overview

BIOS initialization

 Peripheral detected

 Boot device selected

 First sector of boot device read and executed

Boot Loader Components

 Boot Loader

 1 st Stage – small, resides in MBR or boot sector

 2 nd Stage – loaded from boot partition

 Minimum Specifications for Linux:

 Label, kernel location, OS root filesystem and Location of the initial ramdisk (initrd)

 Minimum specification for other OS:

 Boot device, label

GRUB and grub.conf

 GRUB – The Grand Unified Bootloader

 Command-line interface available at boot prompt

 Boot from ext2/ext3, ReiserFS, JFS, FAT, minix, or FFS filesystems

 Support MD5 password protection

 /boot/grub/grub.conf

 Changes to grub.conf take effect immediately

 If MBR on /dev/had is corrupted, reinstall the first stage bootloader with:

/sbin/grub-install /dev/hda

Starting the Boot Process: GRUB

 Image selection

 Select with space followed by up/down arrows

on the boot splash screen

 Argument passing

 Change an exiting stanza in menu editing

mode

 Issue boot commands interactively on the

GRUB command line

init Initialization

 init reads its config: /etc/inittab

 Initial run level

 System initialization scripts

 Run level specific script directories

 Trap certain key sequences

 Define UPS power fall/restore scripts

 Spawn gettys on virtual consoles

 Initialize X in run level 5

Kernel Initialization

 Kernel boot time functions

 Device detection

 Device driver initialization

 Mounts root filesystem read only

 Loads initial process (init)

 Important tasks include:

 Activate udev and selinux

 Sets kernel parameters in /etc/sysctl.conf

 Sets the system clock

 Loads keymaps

 Enables swap partitions

 Sets hostname

 Root filesystem check and remount

 Active RAID and LVM devices

 Enable disk quotas

System V run levels

 Run level defines which services to start

 Each run level has a corresponding directory

Daemon Processes

 A daemon process is a program that is run

in the background, providing some sytem service

 Two types of daemons:

 Standalone

 Transient – Controlled by the “Super-daemon”

xinetd

 Run after the run level specific scripts

 Common place for custom modification

 In most cases it is recommended that you create a System V init script in

 /etc/rc.d/init.d unless the service you are starting is so trivial it doesn’t warrant it Existing scripts can be used as a starting point

Virtual Consoles

 Multiple independent VT100-like terminals

 Defined in /etc/inittab

 Accessed with Ctrl-Alt-F_key from an X session

 /dev/ttyn: virtual console n

 /dev/tty0: the current virtual console

 Default RedHat Enterprise Linux Configuration

 12 consoles defined

 Consoles 1-6 accept logins

 X server starts on the first available console, usually 7.

Controlling Services

 Utilities to control default service startup

and X interface

consoles

works well and is usable with scripts and Kickstart

installations

 Utilities to control services manually

chkconfig: immediately starts and stop

System Reboot

 Rebooting rarely fixes problem in Linux

 If you feel a reboot is necessary try bringing

the system down to runlevel 1 and the back up

to runlevel 3 or 5 This is much faster than a reboot.

 Rebooting the system:

 shutdown –r now

 reboot

 init 6

Unit 3

 Kernel Services and Configuration

Kernel Modules

 Modular kernel components

 Components that need not be resident in the kernel for all configurations and hardware

 Peripheral device drivers

Kernel Module Configuration

 Module examination: /sbin/modinfo

 Parameters, license

 Module Configuration: /etc/modprobe.conf

 Aliases, parameters, actions

 Module Dependencies: modules.dep,

depmod

 Manual control: insmod, rmmod

The /proc filesystem

 /proc is a vital filesystem containing

information about the running kernel

 Contens of “files” under /proc may be

viewed using cat

 Example

 cat /proc/interrupts

 Provides information on system hardware, networking settings and activity, memory

The /proc filesystem, cont’d

 /proc subdirectories

 The /proc/sys subdirectory allows administrators to modify certain parameters of a running kernel

/proc/sys configuration with sysctl

 /proc/sys modifications are temporary and not saved at system shutdown

 The sysctl command manages such

settings in a static and centralized fashion:

 /etc/sysctl.conf

 sysctl is called at boot time by rc.sysinit

and uses setting sin /etc/sysctl.conf

General Hardware Resources

 dmesg and /var/log/dmesg

System Bus Support

Hotswappable Bus Support

 USB and IEEE 1394 Buses

 /sbin/hotplug, (/etc/hotplug/)

 Information in /proc/bus subdirectories

 /sbin/lsusb and /sbin/usbmodules utilities

 USB devices in /dev/usb

 PCMCIA Bus

 /sbin/cardmgr, (/etc/pcmcia/)

 Information in /proc/bus/pccard

 /sbin/cardctl utility

System Monitoring and Process Control

 top, gnome-system-monitor  display

snapshot of processes

 ymstat – reports virtual memory stats

 iostat – lists information on resource

usage, including I/O statistics

 free – summary of system memory usage

 renice – change priority of a process

 kill – send system signal to a process

Unit 4

 Filesystem Management

System Initialization: Device

Recognition

 Master Boot Record (MBR) contains:

 Executable code to load operating system

 Space for partition table information,

including:

 Partition id and type

 Starting cylinder for partition

 Number of cylinder for partition

Disk Partitioning

 An extended partition points to additional partition descriptors

 Total maximum number of partitions

supported by the kernel:

 63 for IDE drives

 15 for SCSI drives

 Why partition drives?

 Containment, performance, quotas, recovery

 Partprobe – reinitializes the kernel’s in

memory version of the partition table

Managing Data: Filesystem creation

Journaling for ext2 filesystems: ext3

 ext3 is essentially an ext3 filesystem that uses a journal for file transaction

automatically

 ext3 filesystems can be created natively or easily converted from ext2

 Ext3 has three journaling modes:

 Ordered – the default, journals only meta-data

 Journaled – Journals data as well as meta-data

 Writeback – Journals updates are not

Managing data: mount

 mount [options] [device] [mount_point]

 device (or filesystem label) points to the filesystem to mount

 mount_point is the directory under which the files on the filesystem will be located

Managing Data: mount options

 -t vfstype (vfat, ext2, ext3, iso9660, etc.)

 Not normally needed

 -o options

 Default options for the ext2/ext3 filesystem:

 rw, suid, dev, exec, auto, nouse, and async

Managing Data: Unmounting

Filesystems

 A filesystem “in use” may not be

unmounted

 Use fuser to check and/or kill processes

 Use the remount option to change a

mounted filesystem’s options

“automatically”

 mount –o remount,ro /data

Managing Data: Filesystem Labels

 Alternate way to refer to devices

 Device independent

 e2lable <special_dev_file>

 mount [options] LABEL=fslabel mount_point

Managing Data: mount, by example

 Sample filesystem requirements met using options:

 Disabling execute access

 Mounting a filesystem image

 Mounting a pc-compatible filesytem.

 Disabling access time updates.

 Setting up a mount alias

Managing Data: Connecting Network Resources

 Mounting NFS resources

 Requires hostname or address of server

 Requires name of exported directory

 Mounting SMB resources

 Requires hostname and address of server

 Requires share name

 May require username and password

Managing Data: /etc/fstab

 Configuring of the filesystem hierarchy

 Used by mount, fsck, and other programs

 Maintains the hierarchy between system reboots

 May use filesystem volume labels in the device field

Managing Data: The auto-Mounter

 System administrator specifies mount

points to be controlled by the automounter daemon process

 The automounter monitors access to these directories and mount the filesystem on

request

 Filesystems automatically unmounted after

a specified interval of inactivity

 Enable /etc/auto.net to “browse” all NFS

ext2/ext3 Filesystem Attributes

 ext2 and ext3 support attributes that

affect the manipulation of the file data

 lsattr display file attributes

 chattr changes file attributes

 Some attributes are not currently supported by the Linux kernel.

Virtual Memory

 Swap space is supplement to system RAM

 Basic setup involves:

 Create swap partition or file

 Write special signature using mkswap

 Add appropriate entries to /etc/fstab

 Activate swap space with swapon -a

Filesystem Maintenance

 Maintaining consistency with fsck

 Filesystems checked at boot up

 sulogin session started if errors are sever

 Verify with fdisk –l and cat /proc/partitions

 Create filesystems for new partitions, or

 Write signature to new swap partitions

 Optionally create disk label

Create any needed mount points

Unit 5

 Network Configuration

Device Recognition

 All drivers for network interface cards are built as module

 Networking scripts reference logical

interface names, eg:

 eth0

 /etc/modprobe.conf maps logical names to specific module name

 Example:

ifconfig

 Used to configure and set IP address on network interfaces

 Not Usually called directly, but by other scripts

 Also used to view properties of active and inactive network interfaces

 if (up | down) interface

 Start and Stop network interfaces

 Take care of details specific to interface

 Changing/adding/deleting routes

 Obtains addresses as needed

 BOOTP, DHCP