Login Problems

Login Problems

When a user/root try to login to Linux system there are so many problems which will prevent the root/user not to login.

Here we will see what are the problems which will prevent user from not to login to system and try to resolve them one by one.

We can divide these problems in to two categories:

1. Physically present at system.
2. Accessing system from remote location(through network).
   

Logging in to the system when you are present infront of the system.

Issue1:Check weather the password you are typing is correct or not, what I mean is Case sensitive etc,
here I am considering that you forgot the password for that system, In this case follow these steps

Issue2:Still not able to login to system except runlevel1, so how to resolve this issue?

• Check root user properties such as shell type, age and security etc?

Step1 : Check the root properties by using finger command.

#finger root
Login: root Name: root
Directory: /root Shell: /sbin/nologin
Never logged in.

this command will give you the properties of the root user, here we have to check what is the shell he is using, the shell should not be nologin shell. If the shell for the root user is no login shell he will not able to login to system so we have to change the login shell from /sbin/nologin shell to some other shells such as /bin/bash.
To do this we can use chsh command

#chsh -l

This command will display all the shell's installed in your system, to change the shell.

#chsh /bin/bash

then execute finger command to check weather shell has been changed to our required shell or not

#finger root

Step2 : Still not able to login? try if there is any age related issues is there on root user

#chage -l root

It will display the age related info for the root user.
Please increase the age of the root user expiry time

#chage root

Step3 : Still unable to login? Check for security related restriction on root user

Check in /etc/securetty file wether all the entries are there or not(in this file there will be entirs of the terminals from where root user can access the system) check weather tty1 to tty7 and vc1 to vc7 are there or not if they are not there add them and try to login.

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Lost Root password

Lost the Root password

When you lost root password how you can recover and login back in to the system?
To login in to system there are so many ways to get root access depending on security level of the system.
Method1: When there is no password set to access runlevel 1.

Here are the steps to change your root password the most esiest way is as follows..

1. Start your computer when you see Redhat Linux boot loader(GRUB menu where you can see all the Operating system's in the system) select the redhat linux and press "e", and select second line where you can set the temporary runlevel for the system to boot

2. You will notice that now you can edit boot loader command arguments now again press "e" and edit the line to add single or 1 without quots at the end of line.

3. Press enter to return to previous screen

4. Press b to boot with this new argument which will run Linux into single user mode. Please make sure that you see single at the end of line.

5. Now you will get root login with out asking for a password in single user mode.

6. Use "passwd" command to change your password.
#passwd
here it will not ask previous password so you can just enter new password.

7. When updateing the password in runlevel1 if the server is not allowing you to change password giving you error, this is due to /etc/shadow file issue.
In order to resolve this issue execute the following command and then try to change the password

#pwunconv

7.After changing the password just type exit command which will take you to default runlevel of the system or just Reboot and use the new password.

Method2: When GRUB boot loader is protected with a password.
When the GRUB boot loader is protected by a password the above mentioned method will not work, so how to login to the system?
In order to retrive root password we have to have first RHEL cd or a live CD(may be konpics/Ubuntu) .

It is easy to boot using the first Cd.
then enter into the rescue mode
just type linux rescue and boot prompt with out quoat

Now we will be logged in to a normal shell, do the folowing steps
Step1 : change the root partation to /mnt/sysimage

chroot /mnt/sysimage

Step2 : Now just change the password
passwd

Step3 : Exit from rescue mode
#exit
#exit
then login with the new passwd
And if you don't have the correct version CD, you can boot from a live CD,
Mkdir /a
mount ... /a
vi /a/etc/password
delete the password in /etc/shadow for root
Now it will come up with no root password (change immediately).

Method3: This method will give you how to retrive your lost root password, not for changing the root password
So how to recover the root password? We can use Rainbow tables technic to do this.

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New RHCE Examination pattern

Recently from 1st May 2009 RHCE(Red Hat Certified Engineer) exam pattern has been changed. Some of the high lights are as follows.. The examination time has been reduced to 3.5 hours from 5.5 hours as it was previously

1. Previously, there will be two sessions one with 2.5hour(for basic troubleshooting) session and 3hours session(for server and security configurations)
2. But this time The content has be consolidated and reorganized into a single section.
3. Every thing will be installed and given along with Visualization, the candidate should complete that exam is one stretch that is 3.5hrs.
4. As you know RHCE5 SElinux is enabled so prepare along that lines.
5. Main thing to pass this exam is just practice practice practice
   

Get counseling on how to pass RHCE, just fill this form for any quires dont hesitate We will charge for this with minimal amount..

Study Points for the RHCE Exam

Prerequisite skills for RHCT and RHCE

Candidates should possess the following skills, as they may be necessary in order to fulfill requirements of the RHCT and RHCE exams:

• use standard command line tools (e.g., ls, cp, mv, rm, tail, cat, etc.) to create, remove, view, and investigate files and directories
• use grep, sed, and awk to process text streams and files
• use a terminal-based text editor, such as vim or nano, to modify text files
• use input/output redirection
• understand basic principles of TCP/IP networking, including IP addresses, netmasks, and gateways for IPv4 and IPv6
• use su to switch user accounts
• use passwd to set passwords
• use tar, gzip, and bzip2
• configure an email client on Red Hat Enterprise Linux
• use text and/or graphical browser to access HTTP/HTTPS URLs
• use lftp to access FTP URLs

RHCT skills

Troubleshooting and System Maintenance

RHCTs should be able to:

• boot systems into different run levels for troubleshooting and system maintenance
• diagnose and correct misconfigured networking
• diagnose and correct hostname resolution problems
• configure the X Window System and a desktop environment
• add new partitions, filesystems, and swap to existing systems
• use standard command-line tools to analyze problems and configure system

Installation and Configuration

RHCTs must be able to:

• perform network OS installation
• implement a custom partitioning scheme
• configure printing
• configure the scheduling of tasks using cron and at
• attach system to a network directory service, such as NIS or LDAP
• configure autofs
• add and manage users, groups, quotas, and File Access Control Lists
• configure filesystem permissions for collaboration
• install and update packages using rpm
• properly update the kernel package
• configure the system to update/install packages from remote repositories using yum or pup
• modify the system bootloader
• implement software RAID at install-time and run-time
• use /proc/sys and sysctl to modify and set kernel run-time parameters
• use scripting to automate system maintenance tasks
• configure NTP for time synchronization with a higher-stratum server

RHCE skills

Troubleshooting and System Maintenance

RHCEs must demonstrate the RHCT skills listed above, and should be able to:

• use the rescue environment provided by first installation CD
• diagnose and correct boot failures arising from bootloader, module, and filesystem errors
• diagnose and correct problems with network services (see Installation and Configuration below for a list of these services)
• add, remove, and resize logical volumes
• diagnose and correct networking services problems where SELinux contexts are interfering with proper operation.

Installation and Configuration

RHCEs must demonstrate the RHCT-level skills listed above, and they must be capable of configuring the following network services:

• HTTP/HTTPS
• SMB
• NFS
• FTP
• Web proxy
• SMTP
• IMAP, IMAPS, and POP3
• SSH
• DNS (caching name server, slave name server)
• NTP

For each of these services, RHCEs must be able to:

• install the packages needed to provide the service
• configure SELinux to support the service
• configure the service to start when the system is booted
• configure the service for basic operation
• Configure host-based and user-based security for the service

RHCEs must also be able to:

• configure hands-free installation using Kickstart
• implement logical volumes at install-time
• use iptables to implement packet filtering and/or NAT
• use PAM to implement user-level restrictions

Source:http://www.redhat.com/certification/rhce/prep_guide/

Please comment on your experience of RHCE exam

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