redhat trainings day11.ppt

8/21/2019 RedHat Trainings Day11.ppt

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RH133

Red Hat Enterprise Linux

System Administration

Welcome!


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Object ives Day 11

Troubleshooting Understanding Troubleshooting Troubleshooting Procedures

Common Troubleshooting Problems and Solutions

X Windows Problems Booting Problems User Management Problems Basic Network Related Problems

Using Rescue Environment FromCD-ROMNFS, FTP, HTTP Servers

Using Run Level 1 Using Syslogs to Solve Problems


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Understanding Troubleshooting


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What is Troubleshooting?

Troubleshooting help you to diagnose and solve technical problems that are

occurring with your computer.

The process of Troubleshooting is both science and art.

The science comes from the concepts of hypothesis testing,

experimentation, comparison and reproducing results.

The science always to focus on likely causes

The art of troubleshooting comes from realization that operating

system, services and applications do not always work as we hope

or anticipate, or even as their creators hops or anticipate.

The art permits us consider the off-the wall and unlikely as

possibilities


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Golden Rules

Two troubleshooting golden rules:

Prioritize problems according to severity

Spend reasonable amount of time on each problem given its

priority

Try to solve root of problem

Always start from very basic step first

Avoid missing underlying cause

Justify why a certain solution is successful


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Troubleshooting Categories

Two categories of problems:

Hardware-related

Software-related


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Troubleshooting Procedures


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Common Troubleshooting

Problems and Solutions


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X Windows Problems and Solutions

Problems

Unable to load Desktop

Monitor Resolution

Mouse Problem

Hangs While loading Desktop

Solutions

system-config-display

Is xfs is running

[ Try to start service permanently using chkconfig]

Is gpm is running

[ Try to start service permanently using chkconfig] Is /home or /tmp is full

Is user reached a hard quota limit

Is hostname resolved properly


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Booting Problems

Problems

1. Kernel does not load at all, or loads partially before a panicoccurs

2. Kernel loads completely, but panic or fails when it tries tomount filesystem and run /sbin/init

3. No bootloader splash screen or prompt appears

4. Kernel loads completely, and /etc/rc.d/rc.sysinit is started andinterrupted

5. Run Level errors

6. System coming up in emergency mode, asking root

password for maintenance.


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Booting Problems

Solutions

Problem 1

GRUB is misconfigured

Boot Sector is corrupt

Bad BIOS settings Problem 2

Corrupt kernel

Incorrect Parameters passed to the kernel by the bootloader

Problem 3

Bootloader is misconfigured

/sbin/init is corrupted or /etc/inittab is misconfigured

Root filesystem is damaged and unmountable


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Booting Problems

Solutions

Problem 4

/bin/bash is missing or corrupted

/etc/fstab may have an error

Error in RAID or QUOTA specifications Problem 5

/etc/inittab is misconfigured

Service-specific error

Misconfigured X or related services in run level 5

Problem 6

Problem with /etc/fstab file check for labels, using e2labelcommand.

Remount the partitions using

mounto remount, defaults /dev/sda2 /

Press CTRL+D for saving.


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User Management Problems

Problems

Unable to Login

Forgot password

Solutions

User is using nologin shell in /etc/passwd User account is locked

User account is expired, issue chageE NEVER root

User is having no password, use passwd for new password

Change users password [ using runlevel 1 if roots password]

Check for any /etc/nologin file / folder, if found, delete them. Check for permissions on /tmp directory, it should be

rwxrwxrwt, if not, issuechmod 1777 /tmp

Check /etc/pam.d/login file for optional words.

Check /etc/securetty for permissions (600) and #


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Basic Network Related Problems

Problems

Unable to ping to other network

Unable to resolve host name

Network Interface is not up

Unable to display IP-Address Solutions

Use neat / neat-tui command

Enter valid entries for DNS server

Enter valid entries for DHCP server [ If required ]

Enter valid entries for Default Gateway Try to UP Ethernet Interface using ifup command


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Using Rescue Environment


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Rescue Environment From

CD-ROM

NFS Server

FTP Server

HTTP Server


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Steps

CD-ROM

Boot from first RHEL installation CD

Type linux rescue at boot prompt

NFS, FTP and HTTP Server

Boot from first RHEL installation CD Type linux rescue askmethod at boot prompt

[ Note :- use only linux rescuewith using BOOT.ISO disk ]


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Additional Boot Options


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Boot Time Command Arguments

askmethod

This command asks you to select the installation method you would like to

use when booting from the Red Hat Linux CD-ROM.

dd

This argument causes the installation program to prompt you to use a driver

diskette.

driverdisk

This command performs the same function as the dd command and also

prompts you to use a driver diskette during the installation of Red Hat Linux.

expert

This command turns on the following special features:

allows partitioning of removable media

prompts for driver diskette


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lowres

This command forces the graphical (GUI) installation program to run at

a lower resolution (640x480).

resolution=

Tells the installation program which video mode to run. It accepts any

standard resolution, such as 640x480, 800x600, 1024x768, and so on.

textThis command disables the graphical installation program and forces

the installation program to run in text mode.


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Using Syslogs to Solve Problems


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Important Log Files

/var/log/dmesg : Kernel log messages

/var/log/messages : Standard system error messages

/var/log/secure : Security, authentication, and xinetd messages


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Disabling Command Line Access

1. Setting the disable_command_line gconf key

Set the /desktop/gnome/lockdown/disable_command_line key by using GConf editor

2. Disabling Console Switching

/etc/X11/xorg.conf.

Section "Serverflags"

Option "DontVTSwitch" "yes"

EndSection

3. Removing the Open Terminal menu i tem from the desktop backgrou nd menu

gconf-editor -- unsetting the /apps/nautilus/preferences/show_desktop key.


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NIC Bonding

The Linux bonding provides a method for aggregating multiple networkinterfaces into a single logical bonded interface. The behavior of thebonded interfaces depends upon the mode;

Hot standby

Load balancing services.

Additionally, link integrity monitoring may be performed.


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Step-1: Create bond0 configuration file

vi /etc/sysconfig/network-scripts/ifcfg-bond0

Append following lines to it:

DEVICE=bond0

IPADDR=192.168.1.20NETWORK=192.168.1.0

NETMASK=255.255.255.0

USERCTL=no

BOOTPROTO=none

ONBOOT=yes


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Step-2: Modify ifcfg-eth0 file

vi /etc/sysconfig/network-scripts/ifcfg-eth0

Modify/append directive as follows:

DEVICE=eth0

USERCTL=noONBOOT=yes

MASTER=bond0

SLAVE=yes

BOOTPROTO=none


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Step-3: Modify ifcfg-eth1 file

vi /etc/sysconfig/network-scripts/ifcfg-eth1

DEVICE=eth1

USERCTL=no

ONBOOT=yesMASTER=bond0

SLAVE=yes

BOOTPROTO=none


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Step-4: Load bond driver/module

vi /etc/modprobe.conf

alias bond0 bonding

options bond0 mode=balance-alb miimon=100


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Step-5: Test configuration

Load the bonding module

# modprobe bonding

Restart the service

service network restart

Verify

less /proc/net/bonding/bond0

ifconfig


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Restricting users to their home Use rbash i.e. restricted bash shell. A restricted shell is used to set up an

environment more controlled than the standard shell. It behaves identically to bashwith the exception that the following are disallowed or not performed:

Changing directories with cd

Setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

Specifying command names containing /

Specifying a file name containing a / as an argument to the . builtin command Specifying a filename containing a slash as an argument to the -p option to the hash

builtin command

Importing function definitions from the shell environment at startup

Parsing the value of SHELLOPTS from the shell environment at startup

Redirecting output using the >, >|, , >&, &>, and >> redirection operators

Using the exec builtin command to replace the shell with another command

Adding or deleting builtin commands with the -f and -d options to the enable builtincommand

Using the enable builtin command to enable disabled shell builtins

Specifying the -p option to the command builtin command

Turning off restricted mode with set +r or set +o restricted.


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Restricting users to their home

Open /etc/passwd file and setup shell to /bin/rbash

vi /etc/passwd

For example here is a sample entry for user aryan:

aryan:x:500:501::/home/aryan:/bin/rbash


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Questions


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What have we learnt ?

TroubleshootingUnderstanding TroubleshootingTroubleshooting Procedures

Common Troubleshooting Problems and Solutions

X Windows ProblemsBooting ProblemsUser Management ProblemsBasic Network Related Problems

Using Rescue Environment FromCD-ROMNFS, FTP, HTTP Servers

Using Run Level 1Using Syslogs to Solve Problems


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Questions

Day 11 Complete


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Thank You !!!

redhat trainings day11.ppt

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