RH133 - Red Hat Linux System Administration

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RH133 - Red Hat Linux System Administration

Introduction - RH133: Red Hat Linux System Administration

Copyright
Welcome
Red Hat Enterprise Linux
Red Hat Enterprise Linux Variants
Red Hat Subscription Model
Contacting Technical Support
Red Hat Network
Red Hat Services and Products
Fedora and EPEL
Audience and Prerequisites
Objectives
Pre/Post-Assessments
Lab Exercises
Classroom Network
Notes on Internationalization

Lecture 1 - Administrative Access

Objectives
Console Access
XOrg: Configuring the X11 Server
Review: Remote Access with SSH
Review: Implementing ssh RSA Keys
Remote X Clients
Multiplexing or Sharing Terminal Sessions with screen
Review: Privilege Escalation
Configuring sudo
Domain Management with virt-manager
Domain Management with virsh
End of Lecture 1

Lecture 2 - Package Management

Objectives
Software as Packages
About yum
Enabling Private yum Repositories
Querying with yum
Managing Packages with yum
About the Red Hat Network
Red Hat Network Client

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Creating a Private yum Repository
Advanced Installation and Removal with rpm
Updating to a New Kernel RPM
Advanced Queries with rpm
Verifying with rpm
End of Lecture 2

Lecture 3 - System Services and Security

Objectives
Monitoring System Logs
syslogd and klogd Configuration
Review: Automating Tasks with cron
System crontab Files
Default Daily Cron Jobs
The anacron System
Managing Printers with CUPS
Accurate Time with Network Time Protocol
SELinux
SELinux Policy: Troubleshooting
End of Lecture 3

Lecture 4 - System Initialization

Objectives
Checking Your System State
Runlevels
Controlling Services
Boot Sequence: Detailed Overview
GRand Unified Bootloader (GRUB)
GRUB Components and Configuration
Kernel Initialization
init Initialization
System Initialization
Standalone Service Initialization
Non-Service Startup
Transient Services
End of Lecture 4

Lecture 5 - Kernel Monitoring and Configuration

Objectives
The Linux Kernel
Kernel Components
Kernels and Support Limits
Monitoring Processes and Resources

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Kernel Monitoring and Configuration with

/proc

and

/sys

Kernel Configuration with sysctl
Exploring Hardware Devices
Review of

/dev

Managing Devices With udev
Kernel Modules
Utilizing and Configuring Kernel Modules
The Initial RAM Disk (initrd)
End of Lecture 5

Lecture 6 - Network Configuration

Objectives
Network Interfaces and /sbin/ip
Network Configuration Utilities
Interface Configuration Files
Device Aliases
Configuring the Routing Table
Verifying IP Connectivity
Hostnames
DNS Configuration
Filtering Network Traffic
Network Monitoring Utilities
Ethernet Channel Bonding
End of Lecture 6

Lecture 7 - Filesystem Administration

Objectives
Partitions and Filesystems
Inodes and Directories
Managing Removable Media
Accessing Network File Shares using NFS
Mounting NFS Shares On-Demand
End of Lecture 7

Lecture 8 - Additional Storage

Objectives
Adding New Filesystems
Partitioning a Physical Disk
Making Filesystems
Mounting Filesystems with mount
Mount Points and

/etc/fstab

Unmounting Filesystems
Modifying a Filesystem Superblock

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Adding Virtual Memory
End of Lecture 8

Lecture 9 - User Administration

Objectives
Review: User and Group Databases
Adding a New User Account
Modifying / Deleting User Accounts
Password Aging Policies
Administering Auxiliary Groups
Configuring the Quota System
Managing Quotas
End of Lecture 9

Lecture 10 - Filesystems for Group Collaboration

Objectives
Review: Viewing/Setting Ownership and Permissions
Review: Default File Ownership and Permissions
User Private Groups
Special Directory Permissions
Access Control Lists (ACLs)
Viewing and Managing ACLs
Review: Permission Precedence
Collaborate with Multiple Groups
End of Lecture 10

Lecture 11 - Centralized User Administration

Objectives
Components of Authentication
Enabling Centralized Authentication
Network Information Service (NIS)
NIS Client Tools
Lightweight Directory Access Protocol (LDAP)
LDAP Client Tools
Authentication Configuration In-depth
Name Service Switch (NSS)
Pluggable Authentication Modules (PAM)
Configuring Centralized Home Directories
Authentication Review
End of Lecture 11

Lecture 12 - Software RAID

Objectives

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Redundant Array of Inexpensive Disks
Adding a Software RAID Device
Software RAID Monitoring
Software RAID Recovery
End of Lecture 12

Lecture 13 - Logical Volume Management

Objectives
What is Logical Volume Manager (LVM)?
LVM Tools
Creating Logical Volumes
Resizing Logical Volumes
Resizing Volume Groups
Logical Volume Manager Snapshots
Using LVM Snapshots
End of Lecture 13

Lecture 14 - Virtualization and Automated Installation

Objectives
Virtualization with Xen
Preparing Domain-0
Installing a New Domain-U
Install Automation with Kickstart
Starting a Kickstart Installation
Anatomy of a Kickstart File
Kickstart: Commands Section
Kickstart: Commands Section
Kickstart: Packages Section
Kickstart: Scripts Section
Creating a Network Installation Server
End of Lecture 14

Lecture 15 - Troubleshooting with Rescue Mode

Objectives
Method of Fault Analysis
Gathering Additional Data
Things to Check: Boot Process
Recovery Runlevels
Filesystem Problems During Boot
Rescue Environment
Rescue Environment Utilities
Rescue Environment Details
End of Lecture 15

RH133 - Red Hat Linux System Administration

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Appendix A - Working with Virtual Systems

Working with Virtual Systems
Working with Virtual Systems

Introduction

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Introduction

RH133: Red Hat Linux System

Administration

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Copyright

The contents of this course and all its modules and related materials,

Hat, Inc.
No part of this publication may be stored in a retrieval system,

transmitted or reproduced in any way, including, but not limited to,

photocopy, photograph, magnetic, electronic or other record, without

the prior written permission of Red Hat, Inc.
This instructional program, including all material provided herein, is

supplied without any guarantees from Red Hat, Inc. Red Hat, Inc.

assumes no liability for damages or legal action arising from the use or

misuse of contents or details contained herein.
If you believe Red Hat training materials are being used, copied, or

otherwise improperly distributed please email training@redhat.com or

phone toll-free (USA) +1 866 626 2994 or +1 919 754 3700.

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Welcome

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Welcome

Please let us know if you need any special assistance while

visiting our training facility.

Please introduce yourself to the rest of the class!

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Red Hat Enterprise Linux

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Red Hat Enterprise Linux

Enterprise-targeted Linux operating system
Focused on mature open source technology
Extended release cycle between major versions

With periodic minor releases during the cycle
Certified with leading OEM and ISV products

All variants based on the same code

Certify once, run any application/anywhere/anytime

Services provided on subscription basis

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Red Hat Enterprise Linux Variants

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Red Hat Enterprise Linux Variants

Red Hat Enterprise Linux Advanced Platform

Unlimited server size and virtualization support
HA clusters and cluster file system

Red Hat Enterprise Linux

Basic server solution for smaller non-mission-critical servers
Virtualization support included

Red Hat Enterprise Linux Desktop

Productivity desktop environment
Workstation option adds tools for software and network service

development
Multi-OS option for virtualization

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Red Hat Subscription Model

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Red Hat Subscription Model

Red Hat sells subscriptions that entitle systems to

receive a set of services that support open source

software

Red Hat Enterprise Linux and other Red Hat/JBoss solutions and

applications

Customers are charged an annual subscription fee per

system

Subscriptions can be migrated as hardware is replaced
Can freely move between major revisions, up and down
Multi-year subscriptions are available

A typical service subscription includes:

Software updates and upgrades through Red Hat Network
Technical support (web and phone)
Certifications, stable APIs/versions, and more

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Contacting Technical Support

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Contacting Technical Support

Collect information needed by technical support:

Define the problem
Gather background information
Gather relevant diagnostic information, if possible
Determine the severity level

Contacting technical support by WWW:

http://www.redhat.com/support/

Contacting technical support by phone:

See

http://www.redhat.com/support/policy/sla/contact/

US/Canada: 888-GO-REDHAT (888-467-3342)

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Red Hat Network

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Red Hat Network

A systems management platform providing lifecycle

management of the operating system and applications

Installing and provisioning new systems
Updating systems
Managing configuration files
Monitoring performance
Redeploying systems for a new purpose

"Hosted" and "Satellite" deployment architectures

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Red Hat Services and Products

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Red Hat Services and Products

Red Hat supports software products and services

beyond Red Hat Enterprise Linux

JBoss Enterprise Middleware
Systems and Identity Management
Infrastructure products and distributed computing
Training, consulting, and extended support

http://www.redhat.com/products/

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Fedora and EPEL

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Fedora and EPEL

Open source projects sponsored by Red Hat
Fedora distribution is focused on latest open source

technology

Rapid six month release cycle
Available as free download from the Internet

EPEL provides add-on software for Red Hat Enterprise

Linux
Open, community-supported proving grounds for

technologies which may be used in upcoming enterprise

products
Red Hat does not provide formal support

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Audience and Prerequisites

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Audience and Prerequisites

Audience: Linux or UNIX users, who understand the

basics of Red Hat Enterprise Linux, that desire further

technical training to continue the process of becoming a

system administrator.
Prerequisites: RH033 Red Hat Linux Essentials or

equivalent experience with Red Hat Enterprise Linux.

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Objectives

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Objectives

Control administrative access to Red Hat Enterprise Linux
Manage software packages with yum and rpm
Set up core system services and security
Understand system and service initialization
Monitor the kernel and configure kernel parameters
Set up IPv4 networking
Maintain existing filesystems and integrate new

filesystems
Perform local user and group administration
Enhance user management with SetGID, ACLs, and

quotas
Enable centralized authentication with NIS and LDAP
Implement partitioning with Software RAID and LVM
Install virtual systems with Kickstart
Troubleshoot boot process with rescue mode

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Pre/Post-Assessments

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Pre/Post-Assessments

Some units begin with a pre-assessment

3-5 simple questions about the unit's subject
Just leave blank if you don't know the answer

Questions are asked again at the end of the unit

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Lab Exercises

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Lab Exercises

Labs

Fundamental exercise providing basic goals, reinforcing the

lecture

Lab Solutions

Offers step-by-step detailed methodology
Found for all exercises that do not have specific steps

themselves

Challenge Labs

Advanced exercise, reinforcing more advanced topics from the

lecture
Not all students may have the time to complete

Optional Labs

Optional exercise that may depend on classroom specific

environment

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Classroom Network

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Classroom Network

example.com network (192.168.0.0/24)

instructor.example.com (192.168.0.254)

Main classroom server: Provides DHCP, DNS, routing and other services

stationX.example.com (192.168.0.X)

Student systems

serverX.example.com (192.168.0.X+100)

Virtual server hosted on student stations (Not used in all classes)

remote.test network (192.168.1.0/24)

crackerX.remote.test (192.168.1.X)

Virtual client hosted on student systems (Not used in all classes)

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Notes on Internationalization

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Notes on Internationalization

Red Hat Enterprise Linux supports nineteen languages
Default system-wide language can be selected

During installation
With system-config-language (System->Administration-

>Language)

Users can set personal language preferences

From graphical login screen (stored in ~/.dmrc)
For interactive shell (with LANG environment variable in
~/.bashrc

)

Alternate languages can be used on a per-command basis:

[user@host ~]$ LANG=ja_JP.UTF-8 date

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Lecture 1

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Lecture 1

Administrative Access

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Access and administer text and graphical consoles
Remotely access the system for administration
Gain administrative privilege
Access virtualized systems

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Console Access

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Console Access

Direct administrative access is obtained through

consoles:

Physical Console
Virtual Console

mingetty
prefdm

Serial Console

agetty

System Console

Graphical and remote access is often obtained through:

Pseudoterminal

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XOrg: Configuring the X11 Server

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XOrg: Configuring the X11 Server

Client / server architecture
Server configuration:

Auto-configured as part of installation or even at runtime
Stored in /etc/X11/xorg.conf
Manually: system-config-display [--reconfig]

Client configuration:

Default in /etc/sysconfig/desktop
Runlevel 3: startx
Runlevel 5: prefdm

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Review: Remote Access with SSH

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Review: Remote Access with SSH

Encrypted remote shell

ssh [user@]host

Copy files securely

scp [-rp] source destination
Remote file: [user@]host:/dir/file

Execute commands remotely

ssh [user@]host 'ifconfig eth0'

Configuration in /etc/ssh/ and ~/.ssh/

Can tunnel X11 and other TCP based network traffic
Supports key based authentication

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Review: Implementing ssh RSA Keys

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Review: Implementing ssh RSA Keys

Generate public/private key pair:

$ ssh-keygen -t rsa

Copy public key to remote server:

$ ssh-copy-id -i .ssh/id_rsa.pub user@host

Test:

$ ssh user@host

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Remote X Clients

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Remote X Clients

X protocol communication is unencrypted
Host-based sessions through xhost expose to all users
User-based sessions implemented through xauth
ssh -X host 'Xclientapp'

May automatically install xauth keys on remote machine
Can tunnel X protocol in secure encrypted ssh connection
Sets DISPLAY environment variable

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Multiplexing or Sharing Terminal Sessions with screen

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Multiplexing or Sharing Terminal Sessions

with screen

Start multiple windows from a single parent shell

Windows are independent of each other
Continues to run even if user switches to another window
Detach from parent without stopping programs
Reconnect from same or different physical machine
Share windows with other people

Highly configurable

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Review: Privilege Escalation

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Review: Privilege Escalation

Know a secret: su

$ su -

But the root password must be “shared”

Be on a list: sudo

$ sudo command

Must be configured before use: visudo

Tied to executable: SUID and SGID

$ passwd

Can be used to provide a “back door”

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Configuring sudo

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Configuring sudo

Configure (as root):

# visudo

user MACHINE = (RunAs) COMMANDS

Cmnd_Alias KILL = /usr/bin/kill
student ALL=(ALL) ALL
%wheel ALL=(ALL) NOPASSWD: ALL
barney localhost=(ALL) KILL

Test (as the listed user):

$ sudo priv_cmd

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Domain Management with virt-manager

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Domain Management with virt-manager

Applications->System Tools->Virtual Machine Manager
GUI for virtual machine management

Run/Shutdown VMs
Pause/Unpause VMs
Save/Restore VMs
Access VM physical/serial console

Also includes easy virtual machine installation wizard
Based on libvirt

A toolkit used to interact with the virtualization capabilities on

Linux
Integrates with multiple virtualization environments (Xen, KVM,

etc.)

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Domain Management with virsh

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Domain Management with virsh

Command line management tool
Controlling domains

virsh start domain
virsh shutdown|reboot|destroy domain
virsh suspend|resume domain
virsh save domain state-file
virsh restore state-file
virsh autostart domain

Monitoring

virsh console domain
virsh list [--all|domain]

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End of Lecture 1

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End of Lecture 1

Questions and Answers
Summary

The X Server can be configured with system-config-display
For CLI remote-access, use ssh user@host

Include -X to enable remote-execution of GUI applications

Root privileges can be selectively delegated via sudo
virt-manager and virsh provide GUI and CLI control of virtual

machines

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Lecture 2

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Lecture 2

Package Management

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Add, remove, and manage software using yum
Configure yum to connect to a private repository
Connect to and use the Red Hat Network
Create a private yum repository
Perform advanced tasks with rpm

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Software as Packages

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Software as Packages

package-version-release.arch.rpm

version

- upstream developer version

release

- packager changes (fixes/backports documented in

“changelog”)
arch

- processor architecture of binaries

Contains:

Files Archive: Binaries, Documentation, “Default” Config
Summary, Description, Changelog
Instructions: Dependencies, Pre/Post Install/Uninstall
Signature

Upgrading replaces with newer version or release

.rpmsave

versus .rpmnew

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About yum

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About yum

Command-line front-end to rpm

Introduced with Fedora and Red Hat Enterprise Linux 5
Replacement for up2date

Designed to resolve package dependencies
Can locate packages across multiple repositories

Red Hat Network Hosted or Satellite Servers
Private http/ftp yum repository servers

Graphical front-ends to yum

system-config-packages (pirut)
pup

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Enabling Private yum Repositories

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Enabling Private yum Repositories

Create a file in /etc/yum.repos.d/ for your repository

Name must end in .repo
Contains one or more stanzas:

[repo-name]
name=A nice description
baseurl=http://yourserver.com/path/to/repo
enabled=1
gpgcheck=1

Default settings in /etc/yum.conf

Repository information is cached

Downloaded from above baseurl subdirectory named repodata
To clear the cache: yum clean dbcache|all

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Querying with yum

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Querying with yum

Listing packages and information

yum list [all] [package_glob]
yum list (installed|available|updates...
[package_glob])
yum grouplist
yum info package
yum groupinfo packagegroup

Searching packages and files

yum search searchterm
yum provides filename

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Managing Packages with yum

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Managing Packages with yum

Installing new packages:

yum install package...
yum localinstall rpmfile...
yum groupinstall packagegroup...

Removing:

yum remove package...

Upgrade to later version/release:

yum update [package...]

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About the Red Hat Network

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About the Red Hat Network

Centralized platform for systems management

Hosted, Satellite, Proxy

Web based management interface
Uses HTTPS for all transactions
Entitlements grant access to software channels and

modules

Custom channels can be locally administered
Additional modules support Management, Provisioning, and

Monitoring

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Red Hat Network Client

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Red Hat Network Client

Registration via rhn_register

Select the updates location (RHN or local satellite/proxy)
Enter Account information
Can be automated with rhnreg_ks

Interactive usage

yum uses plug-in for RHN communication
Already configured in /etc/yum/pluginconf.d/rhnplugin.conf

Remote management

Actions queued on RHN server
rhnsd polls RHN every four hours
rhn_check polls immediately

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Creating a Private yum Repository

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Creating a Private yum Repository

Create a directory to hold your packages
Make this directory available via http or ftp
Install the createrepo RPM
Run createrepo -v /dir/packagedir

Creates/Re-creates a repodata subdirectory
Files contain extracted package header information

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Advanced Installation and Removal with rpm

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Advanced Installation and Removal with rpm

Primary RPM options:

Install/Upgrade: rpm -i | -F | -U rpmfile...
Removal: rpm -e package...
Output options: -v, -h
URL support: ftp:// (with globbing), http://

Advanced options:

Reinstall: --replacepkgs
Downgrade: --oldpackage
Ignore conflicts: --replacefiles
Ignore dependencies: --nodeps

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Updating to a New Kernel RPM

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Updating to a New Kernel RPM

Kernels are installed in parallel, not upgraded

Do not use rpm -U or rpm -F ! Use rpm -i !
yum properly handles with either update or install

Updating (adding) a kernel

yum update kernel
Boot new kernel to test
Reboot to old kernel if a problem arises
yum remove kernel-oldversion if no problems

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Advanced Queries with rpm

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Advanced Queries with rpm

Four basic types of queries:

Installed version: rpm -q package
All installed: rpm -q -a [package_glob]
Package file (uninstalled): rpm -q -p rpmfile
File owner: rpm -q -f file_path_name

Types of information to query:

-i general information about package
-l list of files in package
Many others that yum cannot provide

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Verifying with rpm

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Verifying with rpm

Installed package file verification:

# rpm -V package
# rpm -V -p rpmfile
# rpm -V -a

Signature verification before package installation:

# rpm --import RPM-GPG-KEY-redhat-release
# rpm -qa gpg-pubkey
# rpm -K rpmfile

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End of Lecture 2

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End of Lecture 2

Questions and Answers
Summary

yum installs packages and their dependencies from remote

repositories
Repositories are configured in yum.conf and
/etc/yum.repos.d/
Red Hat distributes updates via the Red Hat Network
Systems must be registered to access RHN

Usually done during installation or post-install with rhn_register

Registered systems poll for updates via rhnsd
rpm can be used for advanced queries and tasks not suited to

yum

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Lecture 3

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Lecture 3

System Services and Security

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Monitor and configure system logs
Automate tasks with cron
Configure printing
Understand the importance of time synchronization
Describe SELinux service security features

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Monitoring System Logs

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Monitoring System Logs

Centralized logging daemons: syslogd, klogd, auditd
Log file examples:

/var/log/dmesg

: Kernel boot messages

/var/log/messages

: Standard system error messages

/var/log/maillog

: Mail system messages

/var/log/secure

: Security, authentication, and xinetd

messages
/var/log/audit/audit.log

: Kernel auditing messages

Application log files and directories also reside in
/var/log/

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syslogd and klogd Configuration

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syslogd and klogd Configuration

klogd traps kernel messages to syslogd
Both controlled by /etc/rc.d/init.d/syslog

Script configured in: /etc/sysconfig/syslog

SYSLOGD_OPTIONS="-m 0"

Configuring syslogd:

/etc/syslog.conf

facility.priority log_location

logger generates messages to syslogd from

command-line

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Review: Automating Tasks with cron

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Review: Automating Tasks with cron

Used to schedule recurring events
Use crontab to edit, install, and view job schedules

crontab [-u user] file
crontab [-l|-r|-e]
echo '*/15 8-17 * * 1-5 echo Breaktime' | crontab

Restrict / allow user access to crond

/etc/cron.allow

/etc/cron.deny

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System crontab Files

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System crontab Files

Different format than user crontab files
Default /etc/crontab runs executables in

/etc/cron.hourly/

/etc/cron.daily/

/etc/cron.weekly/

/etc/cron.monthly/

/etc/cron.d/

contains additional system crontab files

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Default Daily Cron Jobs

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Default Daily Cron Jobs

tmpwatch

Cleans old files in specific directories
Keeps /tmp from filling up

logrotate

Keeps log files from getting too large
Configuration in: /etc/logrotate.conf and
/etc/logrotate.d/

logwatch

Provides a summary about system activity
Reports suspicious messages
Configuration in: /etc/logwatch/

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The anacron System

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The anacron System

anacron runs jobs when the system boots
Configuration file: /etc/anacrontab

Field 1: if the job has not been run in this many days...
Field 2: wait this number of minutes before running it
Field 3: job identifier
Field 4: the job to run

Default is tied to /etc/crontab

Runs “missed” daily, weekly, and monthly jobs
Vital for computers that are not up continually

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Managing Printers with CUPS

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Managing Printers with CUPS

Configuration tools

system-config-printer
Web based:

http://localhost:631

Command line: lpadmin and lpinfo

Configuration files

/etc/cups/cupsd.conf

/etc/cups/printers.conf

PPD files used to describe printers
Uses the Internet Printing Protocol (IPP)

Allows remote browsing of printer queues
Based on HTTP/1.1

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Accurate Time with Network Time Protocol

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Accurate Time with Network Time Protocol

Many applications require accurate timing
Workstation hardware clocks tend to drift without

correction
NTP counters the drift by manipulating the length of a

second
NTP clients should use three time servers
Configuration tool: system-config-date
Configuration file: /etc/ntp.conf
Test with ntpq

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SELinux

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SELinux

Mandatory Access Control -vs- Discretionary Access

Control

Any action not explicitly allowed is denied by default

A binary policy defines:

Security contexts (credentials)
Rules to allow specific actions
Booleans to conditionally enable or disable rules
Audit requirements (logging)

Default policy is targeted

Protects the system from a compromised service, not from local

users
Most local processes are unconfined_t

Supplemental Media

Security Engineer Dan Walsh on the role of SELinux

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SELinux Policy: Troubleshooting

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SELinux Policy: Troubleshooting

Modes: Enforcing, Permissive, or Disabled

Persistent

/etc/sysconfig/selinux
system-config-securitylevel

Runtime

getenforce and setenforce 0 | 1
Kernel arguments: selinux=0 | 1 or enforcing=0 | 1

Logs: /var/log/{messages,audit/audit.log}
General advice

man -k selinux
setroubleshootd, sealert -b and sealert -a
Advises how to avoid errors, not ensure security!

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End of Lecture 3

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End of Lecture 3

Questions and Answers
Summary

Most system logs are stored in /var/log/
Automated jobs can be scheduled with crontab -e

Syntax documented in man 5 crontab

Printers can be configured with system-config-printer
Network Time Protocol synchronizes date and time between

systems

Configure with system-config-date

SELinux identifies and limits processes by type
SELinux mode can be controlled with system-config-

securitylevel

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Lecture 4

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Lecture 4

System Initialization

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Check your current system state
Start, stop and check services
Change to different runlevels
Understand the boot sequence

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Checking Your System State

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Checking Your System State

Red Hat Enterprise Linux Release:

cat /etc/redhat-release

Identifying your kernel:

Current kernel: uname -r
Available kernels: yum list installed kernel\* or rpm -qa

kernel\*

Identifying the runlevel:

Current runlevel: /sbin/runlevel or who -r
Default runlevel: grep initdefault: /etc/inittab

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Runlevels

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Runlevels

init defines runlevels 0-6, S, and emergency

Defines sets of services to auto-start

The runlevel is selected by either

Default in /etc/inittab at boot

id:5:initdefault:

Passing an argument from the bootloader
Using the command init new_runlevel

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Controlling Services

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Controlling Services

Graphical: system-config-services
Standalone Services

Transient Services

chkconfig --list servicename
chkconfig servicename on|off

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Boot Sequence: Detailed Overview

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Boot Sequence: Detailed Overview

BIOS initialization
Bootloader
Kernel initialization
init starts and enters desired runlevel by executing:

/etc/rc.d/rc.sysinit

/etc/rc.d/rc

and /etc/rc.d/rc[0-6].d/

/etc/rc.d/rc.local
Virtual consoles
X Display Manager if appropriate

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GRand Unified Bootloader (GRUB)

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GRand Unified Bootloader (GRUB)

Image selection

Select with space followed by up/down arrows on the boot

splash screen

Argument passing

Change an existing stanza in menu editing mode
Issue boot commands interactively on the GRUB command line

Password protection

Can block image selection
Can block menu editing mode

pyGRUB used for Xen paravirtualized systems

Boot system using: xm create -c domain

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GRUB Components and Configuration

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GRUB Components and Configuration

1st Stage

Small, added to MBR or boot sector during installation
Use /sbin/grub-install to repair

2nd Stage

Loaded from filesystem containing /boot
Configured in /boot/grub/grub.conf

To boot Linux: title, kernel, root filesystem, and initial

ramdisk

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Kernel Initialization

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Kernel Initialization

Kernel boot time functions

Device detection
Device driver initialization (modules loaded from initrd-
<version>.img

)

Mounts root filesystem read only
Loads initial process (init, PID 1)

Logged to /var/log/dmesg

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init Initialization

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init Initialization

init reads its config: /etc/inittab

Initial runlevel
System initialization scripts
Runlevel specific script directories
Trap certain key sequences
Define UPS power fail / restore scripts
Spawn gettys on virtual consoles
Initialize X in runlevel 5

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System Initialization

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System Initialization

/etc/rc.d/rc.sysinit

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 read-write
Activate RAID and LVM devices
Enable disk quotas
Check and mount other local filesystems
Cleans up stale locks and PID files

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Standalone Service Initialization

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Standalone Service Initialization

/etc/rc.d/rc

defines which standalone services to

start

l5:5:wait:/etc/rc.d/rc 5

Each runlevel has a corresponding directory:

/etc/rc.d/rc5.d/

symbolic links called with a stop argument

symbolic links called with a start argument

The System V init scripts reside in:

/etc/rc.d/init.d/
Behavior configured with files under /etc/sysconfig/

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Non-Service Startup

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Non-Service Startup

/etc/rc.d/rc.local

Runs near the end of the runlevel specific scripts (S99local)
Common place for custom modification

Better practice:

Create a System V init script
Existing /etc/rc.d/init.d/ scripts can be used as a starting

point

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Transient Services

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Transient Services

xinetd manages on-demand services

Less-frequently needed services
Host-based authentication
Service statistics and logging
Service IP redirection

Configuration files:

/etc/xinetd.conf

/etc/xinetd.d/service

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End of Lecture 4

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End of Lecture 4

Questions and Answers
Summary

Understand system runlevels and kernels
Manage system services
Change runlevels
Understand the boot sequence
Use the GRUB bootloader
Access virtualization consoles

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Lecture 5

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Lecture 5

Kernel Monitoring and Configuration

RH133-RHEL5u4-en-7-20090928/35efbaa5title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Understand the purpose and organization of the kernel
Know how to configure the kernel using /proc and

sysctl
Explore hardware devices available on the system
Understand how to load and configure kernel modules

RH133-RHEL5u4-en-7-20090928/35efbaa5objectives

The Linux Kernel

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The Linux Kernel

The kernel constitutes the core part of the Linux

operating system
Kernel duties:

System initialization: detects hardware resources and boots up

the system
Process scheduling: determines when processes should run and

for how long
Memory management: allocates memory on behalf of running

processes
Security: enforces permissions, SELinux contexts and firewall

rules
Provides buffers and caches to speed up hardware access
Implements standard network protocols and filesystem formats

Documentation available in the kernel-doc RPM

package

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Kernel Components

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Kernel Components

Multiple kernels may be installed at the same time

Different variants have different features, allows easier version

upgrades

Kernel version is part of the absolute filename to avoid

conflicts
/boot/vmlinuz-version

Main kernel binary file

/boot/initrd-version.img

Initial RAM disk providing critical kernel modules at boot

/lib/modules/version/

Kernel modules (drivers and extensions) matching a particular

kernel binary

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Kernels and Support Limits

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Kernels and Support Limits

RHEL 5.4 32-bit x86 kernels:

kernel

: up to 32 processors, 4 GB RAM

kernel-PAE

: up to 32 processors, 16 GB RAM (PAE36)

kernel-xen

: up to 32 processors, 16 GB RAM (Dom0 limits)

RHEL 5.4 64-bit x86-64 kernels:

kernel

: up to 64 processors, 512 GB RAM

kernel-xen

: up to 126 processors, 512 GB RAM (Dom0 limits)

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Monitoring Processes and Resources

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Monitoring Processes and Resources

Kernel state: uname, uptime, tload
Processes: ps, top, gnome-system-monitor
Memory: free, vmstat, swapon -s, pmap
Disk Utilization: df, fdisk -l, iostat, lsof
Support Summary: sosreport

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Kernel Monitoring and Configuration with /proc and /sys

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Kernel Monitoring and Configuration with
/proc

and /sys

Virtual filesystems: proc and sysfs
Used to display:

Process information: /proc/<PID>
Memory resources: /proc/meminfo
Disk partitions: /proc/partitions

Modify kernel configuration:

System hostname: /proc/sys/kernel/hostname
Apply immediately, but do not persist across a reboot

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Kernel Configuration with sysctl

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Kernel Configuration with sysctl

sysctl adds persistence to /proc/sys settings
Statements added to /etc/sysctl.conf automatically

processed during boot
Configuration maintained or monitored using the sysctl

command:

List all current settings: sysctl -a
Reprocess settings from sysctl.conf: sysctl -p
Set a /proc value dynamically: sysctl -w

net.ipv4.ip_forward=1

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Exploring Hardware Devices

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Exploring Hardware Devices

Utilities:

lspci and lsusb
For x86 and x86-64: dmidecode and x86info

HAL: Hardware Abstraction Layer

Snapshot of all connected devices
hal-device lists in text mode
hal-device-manager displays in a graphical window

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Review of /dev

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Review of /dev

Files under /dev are used to access drivers
Three file attributes determine which driver to access:

Device type (character or block)
Major number
Minor number

Block devices:

/dev/sda

, /dev/sdb - SCSI, SATA, or USB storage

/dev/md0

, /dev/md1 - Software RAID

Character devices:

/dev/null

, /dev/zero - Software devices

/dev/random

, /dev/urandom - Random numbers

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Managing Devices With udev

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Managing Devices With udev

udev manages files stored under /dev/
Files are only created if corresponding device is plugged

in
Files are automatically removed when device is

disconnected
udev statements under /etc/udev/rules.d/

determine:

Filenames
Permissions
Owners and groups
Commands to execute when a new device shows up

mknod does not persist across a reboot

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Kernel Modules

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Kernel Modules

Small kernel extensions
May be loaded and unloaded at will
Can implement drivers, filesystems, firewall, and more
Provided with the kernel RPM

Are located under /lib/modules/$(uname -r)/
Compiled for a specific kernel version

Third party modules may be added

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Utilizing and Configuring Kernel Modules

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Utilizing and Configuring Kernel Modules

lsmod provides a list of loaded modules
modinfo displays information about any available

module
modprobe can load and unload modules
/etc/modprobe.conf

used for module configuration:

Parameters to pass to a module whenever it is loaded
Aliases to represent a module name
Commands to execute when a module is loaded or unloaded

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The Initial RAM Disk (initrd)

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The Initial RAM Disk (initrd)

To mount the root filesystem, the kernel typically needs

to load modules:

ext3

, jbd, raid1, scsi_mod ...

third-party hardware RAID modules

Compressed cpio archive created by kernel installation

kept in /boot
Use mkinitrd to rebuild

# mkinitrd /boot/initrd-$(uname -r).img $(uname -r)

Manually add modules:

--with
/etc/modprobe.conf

/etc/sysconfig/mkinitrd/

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End of Lecture 5

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End of Lecture 5

Questions and Answers
Summary

Different kernel variants based on processor and features
Persistently configure kernel tunables in /etc/sysctl.conf
Hardware and /dev managed through udev and HAL
Currently loaded kernel modules can be listed with lsmod
Modules needed to mount "/" are loaded from initrd

RH133-RHEL5u4-en-7-20090928/35efbaa5summary

Lecture 6

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Lecture 6

Network Configuration

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Configure TCP/IP network interfaces and routing
Configure DNS name resolution
Do basic monitoring and filtering of network traffic
Describe how interfaces could be bonded

RH133-RHEL5u4-en-7-20090928/5be9f76bobjectives

Network Interfaces and /sbin/ip

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Network Interfaces and /sbin/ip

Networking scripts refer to logical interface names:

Ethernet: eth0, eth1 ...
Dial-up: ppp0, ppp1 ...
Loopback: lo

Display network interfaces/configuration by using:

ip [-s] link [show [ethX]]
ip addr [show [ethX]]

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Network Configuration Utilities

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Network Configuration Utilities

system-config-network

Device and Gateway
Static Routes
DNS and Hostname

system-config-network-tui

Device and Gateway

Changes are not immediate

Deactivate and Activate buttons
ifdown ethX ; ifup ethX
service network restart

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Interface Configuration Files

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Interface Configuration Files

/etc/sysconfig/network-scripts/ifcfg-name

Set DEVICE to map configuration to device name
Set HWADDR to map configuration to MAC address
Set BOOTPROTO=dhcp for dynamic configuration
Set IPADDR and NETMASK for static configuration
Set ETHTOOL_OPTS to force speed and duplex settings
Requires at least DEVICE and BOOTPROTO or IPADDR

Options documented in sysconfig.txt

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Device Aliases

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Device Aliases

Useful for virtual hosting
Bind multiple IP addresses to a single NIC

, i.e. eth1:0, eth1:1 ...

Create a separate interface configuration file for each

device alias:

ifcfg-ethX:y
Must use static networking

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Configuring the Routing Table

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Configuring the Routing Table

The routing table tells the kernel how to reach different

networks
Networks are associated with interfaces and, optionally,

routers
Networks attached to interfaces are added

automatically
A default gateway is used if no explicit route is given
View table with ip route
Configure table with:

GATEWAY

in ifcfg-* or /etc/sysconfig/network

Settings in /etc/sysconfig/network-scripts/route-ethX

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Verifying IP Connectivity

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Verifying IP Connectivity

ping

Network packet loss and latency measurement tool

traceroute

Displays network path to a destination

mtr

Combines the functionality of traceroute and ping in a single

tool

These and other tools available in the gnome-nettool

GUI

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Hostnames

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Hostnames

System hostname set in /etc/sysconfig/network

If not explicitly set, DHCP or DNS will be used

Can be viewed or temporarily set with hostname
Other name/IP mappings can be defined in /etc/hosts

127.0.0.1 localhost.localdomain
localhost
::1 localhost6.localdomain6 localdomain6
10.0.0.1 testmachine1.lab.example.com
test1

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DNS Configuration

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DNS Configuration

DNS servers resolve names not in /etc/hosts

Precedence controlled by /etc/nsswitch.conf

Configured in /etc/resolv.conf

search example.com
nameserver 192.168.0.254
nameserver 10.0.0.254

Test with gethostip, host, or dig

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Filtering Network Traffic

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Filtering Network Traffic

Filtering in the kernel
Only inspects packet headers
Consists of:

netfilter modules
iptables command
init.d/iptables

script

Basic policy adjustments with system-config-

securitylevel

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Network Monitoring Utilities

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Network Monitoring Utilities

Network interfaces (ip)

Show what interfaces are available on a system

Local diagnostic (netstat)

Show active connections, routes, and statistics

Port scanners (nmap)

Show what services are available on a system

Packet sniffers (tcpdump, wireshark)

Stores and analyzes all network traffic visible to the "sniffing"

system

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Ethernet Channel Bonding

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Ethernet Channel Bonding

Highly available network interface

Avoids single point of failure
Aggregating bandwidth and load balancing are possible

Many NICs can be bonded into a single virtual interface

Plug each interface into different switches on the same network
Network driver must be able to detect link

Configuration steps:

Load bonding module in /etc/modprobe.conf
Configure bond0 interface and its slave interfaces

/proc/net/bond0/info

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End of Lecture 6

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End of Lecture 6

Questions and Answers
Summary

system-config-network provides GUI or TUI network-

configuration
Network configuration is stored in:

/etc/sysconfig/network-scripts/ifcfg-*

(interface-specific

settings)
/etc/sysconfig/network-scripts/routes-*

(non-standard routes)

/etc/resolv.conf

(DNS servers)

/etc/sysconfig/network

(other global settings)

Basic packet filtering can be configured with system-config-

securitylevel
Bonded interfaces provide aggregated bandwidth and load

balancing

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Lecture 7

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Lecture 7

Filesystem Administration

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Objectives

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Objectives

Upon completion of this unit, you should be able to:

Monitor filesystems
Access removable media
Access data from remote systems using NFS
Mount NFS filesystems on demand

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Partitions and Filesystems

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Partitions and Filesystems

Disk drives are divided into partitions

cat /proc/partitions
fdisk -l /dev/sda
Primary, Extended, Logical

Partitions are formatted with filesystems for users to

store data

Default filesystem: ext3, the Third Extended Linux Filesystem
Other common filesystems: ext2, vfat, iso9660, and gfs

Filesystems are mounted into the tree before access

mount
df [-h]

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Inodes and Directories

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Inodes and Directories

The inode table of a filesystem contains a list of all files

df -i

Each inode (index node) of a file contains metadata:

file type, permissions, UID, GID, size and time stamps
the link count (count of path names pointing to this file)
pointers to the file's data blocks on disk

A directory contains a list of filenames

The directory data block contains mapping of filename to inode

number
ls -i

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Managing Removable Media

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Managing Removable Media

Removable media mounted under /media automatically

Mounting performed by graphical environments
HAL (Hardware Abstraction Layer) monitors removable media
HAL automatically mounts when media detected
HAL calls gnome-mount and gnome-umount
Users can call these commands directly

When mounting manually, use /mnt

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Accessing Network File Shares using NFS

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Accessing Network File Shares using NFS

Servers export directories using NFS

# rpcinfo -p nfsserver
# showmount -e nfsserver

Clients mount NFS exported directories to local

directories

Remote directories appear to be local to local users

# mkdir /pub

Remote directories can be manually mounted

# mount nfsserver:/exported/dir /pub

Can be automatically mounted at boot time in /etc/fstab

nfsserver:/exported/dir /pub nfs soft 0 0

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Mounting NFS Shares On-Demand

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Mounting NFS Shares On-Demand

NFS shares can be automatically mounted on demand

using the automounter

No additional server-side configuration required
NFS shares mounted when accessed by any user and umounted

when no longer in use

Two tier configuration:

First tier: /etc/auto.master lists automounting directory and

file that lists mounts within the directory
Second tier specified in /etc/auto.master: lists mount point,

options, and directory to be mounted

All per-server exports accessed automatically via /net

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End of Lecture 7

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End of Lecture 7

Questions and Answers
Summary

Disks are divided into partitions, which contain filesystems
Filesystems are associated with mountpoints using mount
df -h displays a usage summary for each mounted filesystem
Removable media is mounted under /media
To mount an nfs share, run mount nfsserver:/share
/mntpoint
To list shares on an NFS server, run showmount -e nfsserver
NFS shares can be auto-mounted with /etc/fstab or /net

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Lecture 8

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Lecture 8

Additional Storage

RH133-RHEL5u4-en-7-20090928/5b177302title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Add new partitions/filesystems
Troubleshoot filesystems
Add virtual memory

RH133-RHEL5u4-en-7-20090928/5b177302objectives

Adding New Filesystems

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Adding New Filesystems

Identify device
Partition device
Make filesystem
Label filesystem (optional)
Add entry to /etc/fstab
Create mount point
Mount new filesystem

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Partitioning a Physical Disk

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Partitioning a Physical Disk

Backup the partition table

# sfdisk -d /dev/sda > /tmp/partitions.sda

Partition the disk

# fdisk /dev/sda

Restore partition table after major mistake

# sfdisk /dev/sda < /tmp/partitions.sda

Update /proc/partitions

# partprobe /dev/sda

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Making Filesystems

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Making Filesystems

Make the filesystem with a label

# mkfs -t ext3 -L guest_data /dev/sda5

Calls mkfs.ext3 (default mkfs.ext2)

mkfs.ext3 [options] device

Calls specific filesystem utilities like mke2fs

mke2fs [options] device

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Mounting Filesystems with mount

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Mounting Filesystems with mount

Make a mountpoint

# mkdir -p /srv/guest_data

Mount the filesystem

# mount -o rw LABEL=guest_data /srv/guest_data

Default -o options for ext3:

Executable: rw, suid, dev, exec, auto, nouser, and async
Filesystem embedded by anaconda: acl, user_xattr
Overridden by /etc/fstab or command line -o option

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Mount Points and /etc/fstab

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Mount Points and /etc/fstab

Maintains the hierarchy across system reboots

Used by mount, fsck, and other programs
May use filesystem volume labels in the device field

LABEL=/mnt/data /mnt/data ext3 defaults 1 2

mount -a will mount all auto filesystems in
/etc/fstab

Recommended for testing fstab syntax before reboot!

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Unmounting Filesystems

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Unmounting Filesystems

umount [options] device | mount_point
Cannot unmount a filesystem that is in use

Use fuser to check and/or kill processes

Use remount option to change a mounted filesystem's

options

mount -o remount,ro /data

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Modifying a Filesystem Superblock

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Modifying a Filesystem Superblock

View filesystem features

# dumpe2fs /dev/sda5 | less

Change filesystem features

# tune2fs -i0 -c0 /dev/sda5

Display or change the filesystem label

# e2label /dev/sda5
# e2label /dev/sda5 new_label
# blkid -s LABEL
# findfs LABEL=new_label

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Adding Virtual Memory

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Adding Virtual Memory

Swap space is hard disk space that extends system

RAM
Create a swap file (or partition)

# dd if=/dev/zero of=/var/local/swapfile bs=1k count=1M

Write special signature

# mkswap /var/local/swapfile

Add entry to /etc/fstab

/var/local/swapfile swap swap defaults 0 0

Activate swap space

# swapon -a

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End of Lecture 8

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End of Lecture 8

Questions and Answers
Summary

To create a new filesystem:

1. Run fdisk device and create a partition of type Linux.
2. Run mkfs -t fstype partition to create a filesystem
3. Add to /etc/fstab
4. Run mount -a

To create a new swap partition:

1. Run fdisk device and create a new partition of type Linux Swap
2. Run mkswap partition
3. Add to /etc/fstab
4. Run swapon -a

RH133-RHEL5u4-en-7-20090928/5b177302summary

Lecture 9

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Lecture 9

User Administration

RH133-RHEL5u4-en-7-20090928/b862a9d9title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Manage user and group accounts
Set up filesystem quotas

RH133-RHEL5u4-en-7-20090928/b862a9d9objectives

Review: User and Group Databases

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Review: User and Group Databases

User: /etc/passwd and /etc/shadow

Maps name to UID, GID, home directory, and login shell
Maps name to password and expiration

Group: /etc/group and /etc/gshadow

Maps group to GID and user members
Maps group to password and group administrators

Management: system-config-users and/or command

line tools

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Adding a New User Account

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Adding a New User Account

useradd [options] username
Defaults in: /etc/default/useradd and
/etc/login.defs
Equivalent to:

editing /etc/passwd, /etc/shadow, /etc/group, /etc/gshadow
creating and populating home directory from /etc/skel/
setting permissions and ownership

Set account password using passwd
Accounts may be added in a batch with newusers

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Modifying / Deleting User Accounts

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Modifying / Deleting User Accounts

To change fields in a user's /etc/passwd entry you

can:

Edit the file by hand with vipw
Use usermod [options] username

To remove a user either:

Manually remove the user from /etc/passwd, /etc/shadow,
/etc/group

, /etc/gshadow, /var/spool/mail, etc.

Use userdel [-r] username

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Password Aging Policies

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Password Aging Policies

By default, passwords do not expire
Forcing passwords to expire is part of a strong security

policy
Modify default expiration settings in /etc/login.defs
To modify existing users, either:

Edit /etc/shadow by hand
Use chage [options] username

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Administering Auxiliary Groups

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Administering Auxiliary Groups

Creation: groupadd [-g gid] auxgroup
Add users to group (either):

# usermod -aG auxgroup username
# gpasswd -a username auxgroup
# vigr

Rename/Delete: groupmod and groupdel

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Configuring the Quota System

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Configuring the Quota System

Implemented within the kernel

Enabled on a per-filesystem basis
Individual policies for groups or users

Limit by the number of 1K-blocks or inodes
Implement both soft and hard limits

Initialization

Partition mount options: usrquota, grpquota
Initialize database: quotacheck -cugm /filesystem
Start or stop quotas: quotaon, quotaoff

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Managing Quotas

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Managing Quotas

Implementation

Edit quotas directly: edquota username
From a shell: setquota username 4096 5120 40 50 /foo
Define prototypical users: edquota -p user1 user2

Reporting

User inspection: quota
Quota overviews: repquota
Miscellaneous utilities: warnquota

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End of Lecture 9

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End of Lecture 9

Questions and Answers
Summary

system-config-users provides GUI user and group management
useradd, usermod and userdel provide CLI user management

userdel leaves home directory and mail unless -r is provided

groupadd, groupmod and groupdel provide CLI group

management
Quotas can limit by space (kilobytes) or inodes
To enable quotas on a filesystem

1. Edit /etc/fstab, add usrquota and/or groupquota options.
2. Run mount -o remount partition
3. Run quotacheck -cm partition

quotacheck -cgm partition for group quotas

4. Run quotaon -a
5. Define quotas with edquota and/or setquota

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Lecture 10

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Lecture 10

Filesystems for Group Collaboration

RH133-RHEL5u4-en-7-20090928/88a9a6b5title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Manage file security
Create collaborative directories using SetGID
Extend filesystem security with ACLs

RH133-RHEL5u4-en-7-20090928/88a9a6b5objectives

Review: Viewing/Setting Ownership and Permissions

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Review: Viewing/Setting Ownership and

Permissions

View current settings:

$ ls -l filename

Every file is owned by a UID and a GID
Three permission categories: user (owner), group and others

Change user and/or group:

# chown user:group filename
$ chgrp group filename

Change permissions:

$ chmod ugo+x filename
$ chmod 775 filename

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Review: Default File Ownership and Permissions

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Review: Default File Ownership and

Permissions

Ownership is based on the creator:

User is creator
Group is normally creator's primary group

Permissions start with:

Read and Write for files
Read, Write, and eXecute for directories

Permissions are withheld by creator's umask

Non-system users' default umask is 002 (no w for other)
Files will have permissions of 664 (-rw-rw-r--)
Directories will have permissions of 775 (drwxrwxr-x)

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User Private Groups

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User Private Groups

A group of the same name as the user

Automatically created when user is created
User's primary group is this private group
User's new files are assigned to this group

Prevents new files from belonging to a “public” group
May encourage making files “world-accessible”

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Special Directory Permissions

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Special Directory Permissions

SGID is used to create a collaborative directory

When a file is created in a directory with the SGID bit set, it

belongs to the same group as the directory, rather than the

creator's primary group

# chmod g+s directory

Sticky allows only the owner of a file to delete it

Normally users with write permissions to a directory can delete

any file in that directory regardless of that file's permissions or

ownership

# chmod o+t directory

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Access Control Lists (ACLs)

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Access Control Lists (ACLs)

Grant or deny access to multiple users or groups

Non-root users cannot chown files
Avoids users sharing files with chmod 777
Uses same rwx permissions

Implemented as a mount option (acl)

Embedded in filesystem superblock at install time

Backup utilities/scripts may need to be updated to

support

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Viewing and Managing ACLs

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Viewing and Managing ACLs

Viewing:

$ getfacl filename

Modifying (Adding or Changing):

$ setfacl -m u:gandalf:rw filename

Removing (Expunging):

$ setfacl -x u:gandalf filename

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Review: Permission Precedence

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Review: Permission Precedence

Three access categories: User, Group, and Other
Compare process UID to

UID of file => user permissions apply
ACL UID of file => ACL's permissions apply

Otherwise, compare list of process GIDs to

GID of file => group permissions apply
ACL GID of file => ACL's permissions apply
Since there can be multiple matches at this level, it is additive

within this level

If neither match, other permissions apply

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Collaborate with Multiple Groups

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Collaborate with Multiple Groups

ACLs for groups use “g:” instead of “u:”
Automatic ACL setting

New files inherit default ACL (if set) from directory

$ setfacl -m d:g:groupname:rw directory

Defaults for groups can share files with multiple groups

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End of Lecture 10

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End of Lecture 10

Questions and Answers
Summary

chmod g+sw dir creates a fully-collaborative environment

Members of the group that owns dir can create, delete an modify all

files in it

chmod o+t dir creates a limited-collaboration environment

Users with write access can create and delete only their own files.

Collaborative directories with SGID
Filesystem access to a list of users/groups

RH133-RHEL5u4-en-7-20090928/88a9a6b5summary

Lecture 11

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Lecture 11

Centralized User Administration

RH133-RHEL5u4-en-7-20090928/552a371ctitle

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Describe how Red Hat Enterprise Linux accesses user

information
Configure system to use centralized authentication

services

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Components of Authentication

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Components of Authentication

Two types of information are required to log in

Account information: Who is this user?

UID number, default shell, home directory, groups, etc

Authentication Credentials: Is this really the user?

Password, key, retinal scan, etc

Account and authentication information may be stored

remotely

Allows for common logins across multiple systems

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Enabling Centralized Authentication

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Enabling Centralized Authentication

system-config-authentication

Provided by the authconfig-gtk package
Presents GUI interface if possible
Use authconfig-tui to force text-based interface
Also supports making changes via command-line arguments

Supported account information services:

(local files), NIS, LDAP, Hesiod, Winbind/Active-Directory

Supported authentication mechanisms:

(NSS), Kerberos, LDAP, SmartCard, SMB, Winbind/Active-

Directory

Supplemental Media

Developer Nalin Dahyabhai on system-config-authentication

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Network Information Service (NIS)

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Network Information Service (NIS)

Configuration files converted to “maps” on server
Related maps are grouped into “domains”
Clients join a domain and treat its maps like local files
Common maps include:

passwd

group

hosts

Requires installation of ypbind and portmap RPMs
Password hashes are transmitted unencrypted!

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NIS Client Tools

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NIS Client Tools

ypwhich: Displays the name of the NIS server being

used
ypdomainname: Displays or sets the NIS domain to

join
ypcat mapname: Prints the contents of a map from the

server
rpcinfo -p hostname: Verify NIS server (ypserv)

availability

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Lightweight Directory Access Protocol (LDAP)

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Lightweight Directory Access Protocol (LDAP)

Network-accessible database tuned for high read traffic
May also be used for service configs, extended user

info, etc.
More modern implementation than NIS, supports

encryption
Server configuration can be more complex than with

NIS
Requires installation of nss_ldap and openldap RPMs

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LDAP Client Tools

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LDAP Client Tools

Query an LDAP server: ldapsearch

-ZZ: Require an SSL-encrypted connection
-x: Use simple authentication (required without extra

configuration)
-H ldap://hostname[:port]: Connect to specific server

Test SSL connection to server

# openssl s_client -connect hostname:port

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Authentication Configuration In-depth

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Authentication Configuration In-depth

system-config-authentication really does three

things:

Configure Pluggable Authentication Modules (PAM)

Used by applications to authenticate users

Configure the Name Service Switch (NSS) if necessary

Retrieves account information from local files, NIS and LDAP

Configure service-specific configuration files if necessary

/etc/yp.conf

(NIS)

/etc/openldap/ldap.conf

(LDAP)

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Name Service Switch (NSS)

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Name Service Switch (NSS)

Groups information from multiple sources into

"entries":

passwd

: Account information

shadow

: Authentication information

groups

: Group information

Other entries exist, not related to authentication

Entries are defined in /etc/nsswitch.conf
Applications may query NSS directly or via PAM
getent entry displays the contents of an entry

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Pluggable Authentication Modules (PAM)

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Pluggable Authentication Modules (PAM)

Applications delegate authentication to the libpam

library
PAM prompts, validates, and tells app to accept or

reject
Allows all applications to use the same auth process

...though application-specific instructions may also be included

Default configuration uses NSS for most user/auth data
Documentation: /usr/share/doc/pam-<version>/

Supplemental Media

Developer Nalin Dahyabhai on why PAM was developed

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Configuring Centralized Home Directories

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Configuring Centralized Home Directories

Home directories for users may be shared via NFS

Gives users consistent files and settings across systems

autofs can be configured to mount home dirs upon

matches all possible directory names

represents the name of the requested directory

Do not enable on systems where untrusted users may

have root access!

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Authentication Review

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Authentication Review

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End of Lecture 11

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End of Lecture 11

Questions and Answers
Summary

Authentication is configured using system-config-

authentication
User and authentication information are accessed via PAM and

NSS
Information can be stored locally or on a central server
Supported centralized mechanisms include NIS, LDAP and

Kerberos

RH133-RHEL5u4-en-7-20090928/552a371csummary

Lecture 12

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Lecture 12

Software RAID

RH133-RHEL5u4-en-7-20090928/c4a86305title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Configure high-availability storage with RAID
Recover a degraded software RAID array

RH133-RHEL5u4-en-7-20090928/c4a86305objectives

Redundant Array of Inexpensive Disks

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Redundant Array of Inexpensive Disks

Multiple disks grouped together into “arrays”

Benefits include better performance and/or fault tolerance
RAID Level defines “how” grouped
Spare disks can add extra redundancy

Hardware RAID built into add-on card or motherboard

Requires driver (kernel module)
Array generally seen as a SCSI disk: /dev/sda

Software RAID is built into Linux kernel

RAID devices are named: /dev/md0, /dev/md1, and so on
mdadm provides the administrative interface

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Adding a Software RAID Device

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Adding a Software RAID Device

1. Create partitions of type 0xfd (Linux RAID Autodetect)
2. Combine partitions into a RAID device

# mdadm -C /dev/md0 -a yes -l 5 -n 3 partitions...

3. Format the RAID device

# mkfs.ext3 /dev/md0

4. Add an entry to /etc/fstab:

/dev/md0 /mountpoint ext3 defaults 1 2

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Software RAID Monitoring

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Software RAID Monitoring

Log entries are sent to syslogd
Interactively check status with:

# mdadm --detail /dev/md0
# cat /proc/mdstat

mdmonitor provides notification services on the status

Must create/setup /etc/mdadm.conf

MAILADDR=user@mydomain.TLD

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Software RAID Recovery

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Software RAID Recovery

To simulate disk failure

# mdadm /dev/md0 -f /dev/sda1

Recovering from a software RAID disk failure

1. Replace and reboot, or hot-remove if hardware supports it

# mdadm /dev/md0 -r /dev/sda1

2. Add replacement partition into array

# mdadm /dev/md0 -a /dev/sda1

To disassemble/stop a disk array

# mdadm -S /dev/md0

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End of Lecture 12

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End of Lecture 12

Questions and Answers
Summary

RAID coordinates multiple disks to work as one
Spare disks can be designated for auto-recovery in most RAID

levels
RAID devices are created and managed with mdadm

RH133-RHEL5u4-en-7-20090928/c4a86305summary

Lecture 13

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Lecture 13

Logical Volume Management

RH133-RHEL5u4-en-7-20090928/43bbab7etitle

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Use storage more efficiently with logical volumes
Back up logical volumes with minimal risk and

downtime

RH133-RHEL5u4-en-7-20090928/43bbab7eobjectives

What is Logical Volume Manager (LVM)?

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What is Logical Volume Manager (LVM)?

A layer of abstraction that allows easy manipulation of

volumes
Supports resizing of filesystems
Allows filesystems to span multiple physical devices

Block devices are designated as Physical Volumes
One or more Physical Volumes are used to create a Volume

Group
Volume Groups are defined with Physical Extents of a fixed size
Logical Volumes are composed of Physical Extents from Volume

Group
Filesystems may be created on Logical Volumes

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LVM Tools

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LVM Tools

system-config-lvm provides GUI control

System->Administration->Logical Volume Management
Physical View manages PVs in selected volume group
Logical View manages LVs in selected volume group

lvm subcommand provides CLI control

lvm help lists sub-commands
lvm vgdisplay -v lists status of all VGs, LVs and PVs
Each sub-command has a symbolic link to lvm

Allows sub-commands to be called without lvm prefix

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Creating Logical Volumes

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Creating Logical Volumes

1. Prepare underlying block devices

Can use partitions of type 0x8e or software RAID devices

2. Create physical volumes

# pvcreate /dev/hda3

3. Create volume group containing physical volume

# vgcreate vg0 /dev/hda3

4. Create logical volumes inside volume groups

# lvcreate -L 256M -n data vg0

5. Format and mount logical volume (/dev/vg0/data)

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Resizing Logical Volumes

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Resizing Logical Volumes

Growing logical volumes and filesystems

lvextend can grow logical volumes
resize2fs can grow ext3 filesystems online or offline

Shrinking filesystems and logical volumes

Must be done offline (umount)
Requires a filesystem check (e2fsck) first
Filesystem then reduced (resize2fs)
Lastly, lvreduce can then reduce the volume

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Resizing Volume Groups

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Resizing Volume Groups

Volume Groups can be enlarged with:

# vgextend vg0 /dev/sdb1

Volume Groups can be reduced with:

# pvmove /dev/hda3
# vgreduce vg0 /dev/hda3

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Logical Volume Manager Snapshots

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Logical Volume Manager Snapshots

Snapshots are special Logical Volumes that are an exact copy of an

existing Logical Volume at the time the snapshot is created
Snapshots are perfect for backups and other operations where a

temporary copy of an existing dataset is needed
Snapshots only consume space where they are different from the

original Logical Volume

Snapshots are allocated space at creation but do not use it until changes are

made to the original Logical Volume or the Snapshot
When data is changed on the original Logical Volume the older data is copied

to the Snapshot
Snapshots contain only data that has changed on the original Logical Volume

or the Snapshot since the Snapshot was created.

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Using LVM Snapshots

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Using LVM Snapshots

1. Create snapshot of existing Logical Volume

# lvcreate -l 64 -s -n datasnap /dev/vg0/data

2. Mount snapshot

# mkdir -p /mnt/datasnap
# mount -o ro /dev/vg0/datasnap /mnt/datasnap

3. Perform backup
4. Remove snapshot

# umount /mnt/datasnap
# lvremove /dev/vg0/datasnap

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End of Lecture 13

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End of Lecture 13

Questions and Answers
Summary

LVM organizes space into logical groups independent of device

boundaries
LVM components can be managed with lvm or system-config-

lvm
LVM Snapshots allow backing up of read-only filesystems with

minimal downtime

RH133-RHEL5u4-en-7-20090928/43bbab7esummary

Lecture 14

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Lecture 14

Virtualization and Automated

Installation

RH133-RHEL5u4-en-7-20090928/7005d523title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Define virtualization
Interactively install virtual machine
Create and utilize Kickstart files
Set up an anaconda server

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Virtualization with Xen

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Virtualization with Xen

Xen is the basis for virtualization in RHEL 5

Paravirtualized guests running RHEL 5 and RHEL 4.5 and later
Full virtualization for unmodified operating systems

Xen Architecture

Hypervisor runs on hardware directly
Hypervisor boots privileged RHEL 5 domain (“Dom0”)
xend and other supporting services run in Dom0
User Domains (“DomU”) managed by Dom0

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Preparing Domain-0

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Preparing Domain-0

Ensure that hardware supports virtualization
Perform a normal installation of the machine
Ensure that kernel-xen, xen, and virt-manager are

installed

Select Virtualization component at install-time
Verify subscribed to RHN "RHEL Virtualization" channel, install

with yum

Verify xend and libvirtd configured to start on boot
Configure kernel-xen as default kernel and reboot

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Installing a New Domain-U

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Installing a New Domain-U

GUI Wizard: virt-manager

Define the name of the domain
Select VCPUs, RAM, Network, and VBDs
Specify the location of the installer and optionally a kickstart file

CLI Tool: virt-install
DomUs can be configured to start when Dom0 boots:

# chkconfig xendomains on
# virsh autostart domain

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Install Automation with Kickstart

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Install Automation with Kickstart

Scripted installation method

Supports all anaconda features
Template /root/anaconda-ks.cfg is autogenerated during

installs

Configuration utility: system-config-kickstart
Syntax checker: ksvalidator

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Starting a Kickstart Installation

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Starting a Kickstart Installation

Anaconda boot option ks enters Kickstart mode

DHCP based kickstart: ks
Network based kickstart: ks=url
From local medium: ks=hd:device:/path/to/file

Boot media can be modified for custom installations:

Optical media: boot.iso or Installation CD/DVD
USB media: diskboot.img
Network boot with PXE
Other bootloaders such as GRUB

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Anatomy of a Kickstart File

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Anatomy of a Kickstart File

Commands section

Configures the system
Omitted directives are prompted to the user

Packages section

%packages

selects packages and groups for installation

Dependencies are always resolved

Scripts section(s)

Optional section(s) to customize the system
%pre

scripts are run before installation

%post

scripts are run after installation

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Kickstart: Commands Section

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Kickstart: Commands Section

Starting the Installation

Installation Mode

install

performs a fresh install.

upgrade

upgrades an existing installation.

Installation Method:

cdrom
url --url url
nfs --server host --path directory
harddrive --partition=device --dir=/path/to/install_tree

Media Sets

Two available: Client and Server
May contain packages from additional layered products
key

defines the “Installation Number” to access additional

content

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Kickstart: Commands Section

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Kickstart: Commands Section

Important Directives

Required Directives

Must be specified, otherwise the installer configures them

interactively
Localization options: keyboard, lang, timezone
Authentication: rootpw, authconfig
Bootloader: bootloader

Optional Directives

Network: network [options]
Security: firewall, selinux, services
Installer behavior: firstboot, poweroff|reboot, interactive,
text

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Kickstart: Packages Section

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Kickstart: Packages Section

Add package groups with @package_group
Add single packages with package_name (no version)
Remove packages from the list with -package_name
Use wildcards to specify multiple packages
Dependencies are always resolved
Additional languages with @lang-support

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Kickstart: Scripts Section

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Kickstart: Scripts Section

%pre

gives you the first word

Executes as a bash shell script
Executes after Kickstart file is parsed

%post

gives you the final word

Can specify interpreter (bash is default)
chrooted by default, but may be run without chroot

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Creating a Network Installation Server

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Creating a Network Installation Server

Provides an easy distribution platform for the enterprise

Necessary for network-based installs
Often faster than CDROM-based installation methods

Share the media directories

NFS, FTP, and/or HTTP
Can be used as a local yum repository

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End of Lecture 14

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End of Lecture 14

Questions and Answers
Summary

Virtualization allows for more efficient use of hardware

resources
virt-manager provides GUI management of virtual machines
virsh and virt-install provide CLI management of virtual

machines
Kickstart files allow for automation of Red Hat Enterprise Linux

installation
Installation leaves a template kickstart in /root/anaconda-
ks.cfg
system-config-kickstart can be used to create new kickstart

files
ksvalidator can be used to check kickstart file syntax
Network installation can be performed via HTTP, FTP, and NFS

RH133-RHEL5u4-en-7-20090928/7005d523summary

Lecture 15

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Lecture 15

Troubleshooting with Rescue Mode

RH133-RHEL5u4-en-7-20090928/9e12a361title

Objectives

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Objectives

Upon completion of this unit, you should be able to:

Develop a strategy for troubleshooting
Use the rescue environment
Access virtualized disks from Domain-0

RH133-RHEL5u4-en-7-20090928/9e12a361objectives

Method of Fault Analysis

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Method of Fault Analysis

Characterize the problem
Reproduce the problem
Find further information
Eliminate possible causes
Try the easy things first
Configuration files

Backup before changing
Use tools when available

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Gathering Additional Data

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Gathering Additional Data

Useful commands

history
grep
diff
find /dir -cmin -60
strace command
tail -f logfile

Generate additional information

*.debug

in syslog

--debug option in application

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Things to Check: Boot Process

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Things to Check: Boot Process

Bootloader configuration
Kernel

Starting init

/sbin/init
/etc/rc.d/rc.sysinit

Entering runlevel [0-6]

/etc/rc.d/rc, /etc/rc.d/rc[0-6].d/
/etc/rc.d/rc.local
Virtual Consoles
X Display Manager

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Recovery Runlevels

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Recovery Runlevels

Pass runlevel to init

On boot from GRUB splash screen

kernel

line

module

line (Xen)

From shell prompt using: init or telinit

Runlevel 1

Process rc.sysinit and rc1.d scripts

Runlevel s, S, or single

Process only rc.sysinit

emergency

Run sulogin only

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Filesystem Problems During Boot

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Filesystem Problems During Boot

rc.sysinit attempts to mount local filesystems
Upon failure, user is dropped to an sulogin shell
fsck may be used to fix corrupted filesystems
Before running fsck:

Check fstab for mistakes
Before editing:

# mount -o remount,rw /

Manually test mounting filesystems

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Rescue Environment

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Rescue Environment

Required when root filesystem is unavailable
Non-system specific
Boot from installer kernel/initrd

boot: linux rescue

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Rescue Environment Utilities

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Rescue Environment Utilities

Disk Maintenance Utilities

lvm

Networking Utilities
Miscellaneous Utilities
Logging:

/tmp/syslog

/tmp/anaconda.log

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Rescue Environment Details

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Rescue Environment Details

Filesystem reconstruction

Asks if filesystems should be mounted: /mnt/sysimage/*
$PATH

includes hard drive's directories

chroot /mnt/sysimage
NFS method mounted: /mnt/source
Define MANPATH to access man pages

Filesystem nodes

System-specific device files provided
mknod knows major/minor #'s

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End of Lecture 15

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End of Lecture 15

Questions and Answers
Summary

Remember the order of events in the boot sequence:

BIOS
Grub
Kernel

/sbin/init

(reading /etc/inittab)

/etc/rc.d/rc.sysinit
/etc/rc.d/rc runlevel
mingetty/prefdm

Enter linux rescue at boot: prompt for rescue mode
kpartx can be used to examine VM disks

RH133-RHEL5u4-en-7-20090928/9e12a361summary

Appendix A

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Appendix A

Working with Virtual Systems

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Working with Virtual Systems

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Working with Virtual Systems

Connecting to virtual systems

For many labs you will be asked to connect to a virtual server to complete the lab work.

These servers can be accessed in different ways. The preferred way to access these virtual

machines, a.k.a. domains, is via the ssh command. Depending on your classroom

environment there may be other ways to access these machines.

The following sections discuss tools for managing virtual machines in Red Hat Global

Learning Services physical and virtual training environments, respectively:

Working with virtual machines in a physical-classroom environment

Working with virtual machines in a physical-classroom

environment

If you are in a physical classroom environment, ssh is the recommended method for

connecting to virtual machines, but you have alternatives if that does not work. If you

experience problems connecting using ssh, you can try using the following virsh

commands. Extended usage info on these commands can be found in man virsh.

virsh is the command line management tool used for almost all aspects of controlling and

working with virtual systems. It can also be used to get access directly to a serial console

of a virtual system. This is useful for connecting to virtual systems for monitoring installs,

examining the boot process, or for attaching to hosts that may not yet be configured for

network access. virsh must be run from the Dom-0, or host machine, of the virtual hosts.

It can not be run on the virtual systems themselves.

Using virsh to control domains

virsh start

domain

Used to 'power on' a virtual host.
virsh shutdown

domain

Does a 'clean' shutdown of a virtual host.
virsh reboot

domain

Reboots a virtual system.
virsh destroy

domain

Is akin to pulling the power plug.
virsh suspend

domain

'Pauses' the virtual system. The host is still in memory but is no longer running.
virsh resume

domain

Changes a virtual system out of the suspended state back into a running state.
virsh save

domain state-file

Saves the running state of a domain to a file to be restored later. This is roughly the

equivalent of 'hibernating' a virtual system.
virsh restore

state-file

Working with Virtual Systems

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Restore a previously saved domain running state from a virsh save file.

Using virsh to monitor domains

virsh console

domain

Opens a local serial console to a running domain. This gives command-line access to

your virtual system.

Ctrl + ]

Disconnects from the console of a domain.

virsh list [

domain

]

List currently running domains.
xentop

Displays a list of currently running domains and gives information in a constantly

updating format. It is like top for Xen hosts.

Booting virtual systems into recovery runlevels

Virtual systems can be booted into recovery runlevels like emergency and single-user

mode, but the process is different than with a physical system.

1. Shut down the virtual system by clicking Shutdown in virt-manager or running

virsh destroy

domain

from the command line.

2. Boot the virtual system to a boot-loader prompt by running xm create -c

domain

(don't forget the -c option!). This will open a console connection to

domain

in your

terminal, allowing you to access the boot-loader.

3. As soon as you see the boot-loader menu, press

to halt the countdown and begin

appending arguments to the kernel command line.

4. Add

emergency

for emergency mode or

for single user mode to the kernel

arguments and press

Enter

5. Disconnect from the console by pressing Ctrl-]
6. Open a graphical connection to the virtual system by double-clicking on it in virt-

manager, which you can start from the command line or by navigating to

Applications->System Tools->Virtual Machine Manager

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Working with Virtual Systems

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Working with Virtual Systems

Working with virtual machines in a virtual-training environment

In a virtual classroom, your workstations are virtual machines. Because running virtual machines within

another virtual machine is not currently supported, you will not have access to other virtual systems directly

using the virsh command. You should instead use ssh to access your virtual systems, or use the web

interface.

You will have a link in the Virtual Training Tools bar for each of the virtual machines assigned for your class.

To manage any of your virtual machines, click the station

or server

link. You will get a new browser

window that will contain your virtual machine. Near the top of the window you will have buttons to manage

your virtual machine.

Figure A.1. ServerX+100 screenshot

The POWER ON button

Working with Virtual Systems

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The POWER ON button

Use the POWER ON button to boot the machine. This is like pressing the power button on a physical

machine.

The POWER OFF button

Use the POWER OFF button to immediately shut down the machine. This is similar to unplugging the

machine. Optionally you can run the poweroff or shutdown -h now commands from a terminal to

gracefully shut it down.

The KICKSTART button

Use the KICKSTART button to use the instructors kickstart file to rebuild your machine. You will not be able

to interact with the installation--it will be totally automated. Once the machine is done kickstarting, it will

remain in the powered off state. Press the POWER ON button to power it on. This button is only available in

the station

machine.

The RESET button

Use the RESET button to reset your virtual machine using an LVM snapshot. You will have a fresh

installation, and once that is created, it will boot the virtual machine. This button is only available in the

server

machine.

The INSTALL button

Use the INSTALL button to run an interactive installation. It will ask all the question about partitioning,

packages, etc. Once the machine is done installing, it will remain in the powered off state. Press the POWER

ON button to power it on.

The RESCUE button

Use the RESCUE button to send your machine into rescue mode. You will be able to interact with your

installation in a rescue environment.

The CUSTOM (kernel boot args) box

Use the CUSTOM (kernel boot args) box to append arguments to the kernel as you boot. When you press

the POWER ON button, it will pop up a dialog box to verify that you want to power on the machine. This will

include a box for kernel boot arguments. These may include arguments such as single, emergency, 3, etc.

If there is anything in the CUSTOM box when you click the POWER ON button, it will be appended to the

kernel line as an argument.

Figure A.2. Custom boot arguments

Working with Virtual Systems

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Note that if you add any kernel arguments at boot time, and you soft reboot the machine (e.g., typing

reboot at the command line) the same kernel arguments will be used when the virtual machine boots.

The Ctrl-Alt-Del button

Use the Ctrl-Alt-Del button to send a Ctrl-Alt-Del to the virtual machine. Note that GNOME by default

ignores this keystroke, so you may only be able to use it in text mode.

The Ctrl-Alt-... drop-down menu

Use the Ctrl-Alt-... drop-down menu to change virtual terminals. For instance, to change to tty1, click the

Ctrl-Alt-... menu, then press F1. To return to the GUI (tty7), click Ctrl-Alt-... menu, then press F7.

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RH133-RHEL5u4-en-7-20090928/3fe0a14d

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