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Wednesday, January 25, 2012
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The ext3 file system in Linux
The ext3 filesystem, developed by
RedHat extends the popular ext2 filesystem with the introduction of journaling.
What is a Journaling Filesystem?
A journaling filesystem keeps a journal or log of the changes that are being made to the filesystem during disk writing that can be used to rapidly reconstruct corruptions that may occur due to events such a system crash or power outage. The level of journaling performed by the file system can be configured to provide a number of levels of logging depending on your needs and performance requirements.
What are the Advantages of a Journaling Filesystem?
There are a number of advantages to using a journaling files system.
Both the size and volume of data stored on disk drives has grown exponentially over the years. The probelm with a non-journaled file system is that following a crash the fsck (filesystem consistency check) utility has to be run. fsck will scan the entire filesystem validating all entries and making sure that blocks are allocated and referenced correctly. If it finds a corrupt entry it will attempt to fix the problem. The issues here are two-fold. Firstly, the fsck utility will not always be able to repair damage and you will end up with data in the lost+found directory. This is data that was being used by an application but the system no longer knows where they were reference from. The other problem is the issue of time. It can take a very long time to complete the fsck process on a large file system leading to unacceptable down time.
A journaled file system records information in a log area on a disk (the journal and log do not need to be on the same device) during each write. This is a essentially an "intent to commit" data to the filesystem. The amount of information logged is configurable and ranges from not logging anything, to logging what is known as the "metadata" (i.e ownership, date stamp information etc), to logging the "metadata" and the data blocks that are to be written to the file. Once the log is updated the system then writes the actual data to the appropriate areas of the filesystem and marks an entry in the log to say the data is committed.
After a crash the filesystem can very quickly be brought back on-line using the journal log reducing what could take minutes using fsck to seconds with the added advantage that there is considerably less chance of data loss or corruption.
What is a Journal Checkpoint?
What is a Journaling Filesystem?
A journaling filesystem keeps a journal or log of the changes that are being made to the filesystem during disk writing that can be used to rapidly reconstruct corruptions that may occur due to events such a system crash or power outage. The level of journaling performed by the file system can be configured to provide a number of levels of logging depending on your needs and performance requirements.
What are the Advantages of a Journaling Filesystem?
There are a number of advantages to using a journaling files system.
Both the size and volume of data stored on disk drives has grown exponentially over the years. The probelm with a non-journaled file system is that following a crash the fsck (filesystem consistency check) utility has to be run. fsck will scan the entire filesystem validating all entries and making sure that blocks are allocated and referenced correctly. If it finds a corrupt entry it will attempt to fix the problem. The issues here are two-fold. Firstly, the fsck utility will not always be able to repair damage and you will end up with data in the lost+found directory. This is data that was being used by an application but the system no longer knows where they were reference from. The other problem is the issue of time. It can take a very long time to complete the fsck process on a large file system leading to unacceptable down time.
A journaled file system records information in a log area on a disk (the journal and log do not need to be on the same device) during each write. This is a essentially an "intent to commit" data to the filesystem. The amount of information logged is configurable and ranges from not logging anything, to logging what is known as the "metadata" (i.e ownership, date stamp information etc), to logging the "metadata" and the data blocks that are to be written to the file. Once the log is updated the system then writes the actual data to the appropriate areas of the filesystem and marks an entry in the log to say the data is committed.
After a crash the filesystem can very quickly be brought back on-line using the journal log reducing what could take minutes using fsck to seconds with the added advantage that there is considerably less chance of data loss or corruption.
What is a Journal Checkpoint?
When a file is accessed on the
filesystem, the last snapshot of that file is read from the disk into memory.
The journal log is then consulted to see if any uncommitted changes have been
made to the file since the data was last written to the file (essentially
looking for an "intention to commit" in the log entry as described
above). At particular points the filesystem will update file data on the disk
from the uncommited log entries and trim those entries from the log. Committing
operations from the log and synchronizing the log and its associated filesystem
is called a checkpoint.
What are the disadvantages of a
Journaled Filesystem?
Nothing in life is is free and ext3 and journaled filesystems are no exception to the rule. The biggest draw back of journaling is in the area of performance simply because more disk writes are required to store information in the log. In practice, however, unless you are running system where disk performance is absolutely critical the performance difference will be negligable.
What Journaling Options are Available with the ext3 filesystem?
The ext3 filesystem provides three options. These are as follows:
Nothing in life is is free and ext3 and journaled filesystems are no exception to the rule. The biggest draw back of journaling is in the area of performance simply because more disk writes are required to store information in the log. In practice, however, unless you are running system where disk performance is absolutely critical the performance difference will be negligable.
What Journaling Options are Available with the ext3 filesystem?
The ext3 filesystem provides three options. These are as follows:
- writeback - greater speed at the price of limited data integrity. Allows old data to show up in files after a crash and relies on kernel's standard writebacks to flush buffers.
- ordered - that the data is consistent with the file system; recently-written files will never show up with garbage contents after a crash at the cost of some speed.
- journal - Journals all data requiring greater journal space and reduced performance. The most secure data retention policy.
Does
the Journal log have to be on the same disk as the filesystem?
No, the ext3 journal log does not have to be on the same physical device as the filesystem it is logging. On a RedHat Linux the journal device can be specified using the journal_device= option with the -journal-options command line argument of the tune2fs utility.
No, the ext3 journal log does not have to be on the same physical device as the filesystem it is logging. On a RedHat Linux the journal device can be specified using the journal_device= option with the -journal-options command line argument of the tune2fs utility.
How to check Previous IP ADdress Details in windows Machines
How to check previous IP address details if customer not aware about it.
Release
Windows XP
Problem
After replacing motherboard customer not aware about previous IP address details.
Solution
In this case using registry we can find out previous IP address details, Windows Registry path should be specified below:
Current and previous IP address details will list under:
“HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Prameters\Interfaces”
Windows Explorer has stopped working Error in Windows 7
Windows Explorer has stopped working Error in Windows 7
Problem:
The most annoying error messages in Windows Operating system are "Windows Explorer has stopped working" - "Windows Installer has stopped working".
Operating system:
Windows vista,Windows 7
Suggested Solutions:
Method1:
Go to the Start button.
In the Search box, type "regedit" (without quotes) and press Enter.
Browse the following registry key: "HKEY_LOCAL_MACHINE\SOFTWARE\ Microsoft\ SQMClient\Windows\DisabledSessions".
On the right window pane, delete the subkey: "Machine Throttling".
Reboot your computer.
Method 2:
In Administrator mode, At the command prompt, type "chkdsk /r /f" (without quotes) and press Enter. Restart the System.
Method 3:
Incompatible Drivers installed while updating the Sound Card,Graphics Card, LAN Drivers etc. So Roll back the driver that you installed recently.It may also happen due to old drivers. Go the official download page for the respective hardware to get the driver updated.
Method 4 :
Press the key combination Windows logo key + R to open the Run dialog.
Type gpedit.msc in the Run dialog and press Enter.
In the Local Group Policy Editor navigate to
Computer Configuration → Administrative Templates → System → Internet Communication Management → Internet Communication Settings.
You would find a setting on the right hand side pane — Turn Off Windows Customer Experience Improvement program
Double-click on this setting and choose Enabled and then click OK.
Close the Local Group Policy Editor windows
Bootmgr is missing error in windows 7
Bootmgr is missing error in windows 7
Release
Windows 7
Problem
While booting in to windows 7 showing the error “bootmgr is missing. Press Ctrl+Alt+Del to restart”.
Solution
Method 1:
1. Please insert the Windows 7 DVD media and restart the computer.
2. Choose your language settings, and then click "Next" option.
3. Select the option "Repair your computer".
4. Select the operating system you want to repair, and then click "Next".
5. On the System Recovery Options screen, select the option "Startup Repair". Startup Repair might prompt you to make choices as it tries to fix the problem, and if necessary, it might restart your computer as it makes repairs.
Method 2:
1. Please insert the Windows 7 DVD media and restart the computer
2. Select the option "Repair computer".
3. Select "Cancel" to exit the repair wizard.
4. Select "command prompt" option from the available options
5. Type your "DVD-DRIVE LETTER" in command prompt, press ENTER.
6. Let us assume windows 7 is installed in C drive, type "copy bootmgr c:\" without codes, press ENTER.
7. Type "exit", press ENTER.
8. Restart computer.
9. Select "start windows normally".
Method 3:
1. Please insert the Windows 7 DVD media and restart the computer.
2. Choose your language settings, and then click "Next" option.
3. Select the option "Repair your computer".
4. Select the operating system you want to repair, and then click "Next".
5. In the System Recovery Options dialog box, select Command Prompt.
6. Type Bootrec /RebuildBcd , and then press ENTER.
7.Restart the computer
STOP 0X0000006B (Parameter1,Parameter2, Parameter3,Parameter4 ):PROCESS1_INITIALIZATIO_ FAILED ERROR
"PROCESS1_INITIALIZATION_FAILED” ERROR
Release
Windows 7 Professional (32B)
Problem:
While booting in Windows 7 the following error showing in blue screen.
STOP 0X0000006B (Parameter1, Parameter2, Parameter3, Parameter4):"PROCESS1_INITIALIZATION_FAILED-WINDOWS 7. This problem prevents the system from starting and all options in the boot menu, safe mode, VGA mode, etc. lead to the same BSOD.
Solution:
This issue occurs because the Bootcat.cache file is corrupted or because the size of the Bootcat.cache file is changed since the last successful start.
On computers running any of the Windows NT family (i.e. Windows NT 4.0, Windows 2000 and Windows Xp, Windows Server 2003), the BSOD is caused by a missing DLL file (usually NTDLL.DLL).
To fix this, use Windows CD to boot to the recovery console .Then type
To fix this, use Windows CD to boot to the recovery console .Then type
"dir ntdll.dll"
The dir command allows you to see the available files in that directory. The ntdll.dll file is a file created by Microsoft that has a description of "NT Layer DLL" and is the file that contains NT kernel functions. This file is located in the c:\windows\system32 or c:\winnt\system32 directory and can also be found in the c:\i386 directory.
If it shows, the file may be corrupted. If you get a "file not found" message, then type
"dir ntdll.dll/s"
The file may show up usually in c:\windows\system32\dllcache.If that's the case, then type
"copy dllcache\ntdll.dll "
and you will then get
"1 file(s) copied"
If the file is missing completely, then with the Windows CD in your CD drive, type
"copy [d:]\i386\ntdll.dll " , where [d:] is the letter assigned to your CD drive
Now, reboot the machine.
On computers running any of the Windows Vista family (i.e. all editions of Windows Vista and Windows 7; all editions of Windows Server 2008). The BSOD is caused by a disposable file by the name of "bootcat.cache" located usually in "c:\windows\system32\codeintegrity" which has been corrupted.
If it is an intermittent problem, this can be solve by manually deleting bootcache.cat from C:\Windows\system32\CodeIntegrity
As per Microsoft, there is no hotfix available for this problem. They recommends to update Service Pack 1. We can use the following link to download the Service Pack.
Windows 7 Service Pack 1
Windows 2008 R2 Service Pack 1
If Windows is stuck in a repair and restart loop, insert Windows CD and select command prompt option. Then type,
“del c:\Windows\system32\CodeIntegrity\bootcat.cache”
Then reboot the pc.
Boot.ini tab is missing in MSCONFIG
Boot.ini tab is missing in MSCONFIG
Release
Windows XP SP2
Problem
When we start MSCONFIG.EXE the BOOT.INI tab which usually appears, may be missing
Solution
This problem may simply be a file permissions issue. To check this you can verify that by typing C:\Boot.ini in Start, Run dialog. If you get Access Denied or similar error, that explains the problem. Otherwise checkout the registry entries.
Open Regedit and locate the following path
“HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\MSConfig” .In the right-pane, delete the value named Boot.ini (if found).Close Registry Editor and restart the windows explorer.try to open msconfig
Mapped Drive Connection to Network Share May Be Lost
Mapped Drive Connection to Network Share May Be Lost
Release
Windows 7,Windows 2008 server enterprise
Problem
The mapped drive may be disconnected after a regular interval of inactivity, and Windows Explorer may display a red "X" on the icon of the mapped drive. However, if you try to access or browse the mapped drive, it reconnects quickly.
Solution
This behavior occurs because the systems can drop idle connections after a specified time-out period (by default, 15 minutes) to prevent wasting server resources on unused sessions. The connection can be re-established very quickly, if required.
Method1:
1.Open registry editor and locate the following path
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters
2. In the right pane, click the autodisconnect value, and then on the Edit menu, click Modify. If the autodisconnect value does not exist, follow these steps:
On the Edit menu, point to New, and then click REG_DWORD.
Type autodisconnect, and then press ENTER.
On the Edit menu, click Modify.
Click Hexadecimal.
3. In the Value data box, type ffffffff, and then click OK. Close the registry editor and restart the PC
Error The current printer driver is not compatible with a policy enabled on your computer that blocks Windows NT 4.0 or Windows 2000 kernel mode drivers
Error The current printer driver is not compatible with a policy enabled on your computer that blocks Windows NT 4.0 or Windows 2000 kernel mode drivers
Release
Windows 2003 server SP2,Windows XP
Problem
When you install printer drivers , you may receive the following error message and cannot install printer.
“Unable to Install Printer. The printer driver is not compatible with a policy enabled on your computer that blocks Windows NT 4.0 drivers. If you want to use this driver, contact your system administrator about disabling this policy”
Solution
This behavior occurs because Windows does not support Kernel mode print drivers by default.
For windows XP
Open the group policy editor by typing gpedit.msc on RUN prompt and locate the path
Under Local Computer Policy, double-click Computer Configuration. Double-click Administrative Templates, and then double-click Printers.Right-click Disallow installation of printers using kernel mode drivers, and then click properties.On the Setting tab, click Disabled, and then click OK.
If you enable this the installation of kernel-mode printer drivers will be prevented.
For updating group policy use gpupadte /force command in command prompt
For windows 2003 server
Open the group policy editor by typing gpedit.msc on RUN prompt and locate the path
Under Local Computer Policy, double-click Computer Configuration. Double-click Administrative Templates, and then double-click Printers.Right-click Disallow installation of printers using kernel mode drivers.
or
Default Domain Controller Policy / Computer Configuration / Administrative Templates / Printers / Disallow installation of printers using kernel-mode drivers. And then click properties.On the Setting tab, click Disabled, and then click OK.
For updating group policy use gpupadte /force command in command prompt
Windows Cannot Set a Default Printer
Windows Cannot Set a Default Printer
Release
Windows 2000,Windows XP, Windows Vista, Windows 7
Problem
When we try to set a default printer, after changing the default printer in the printer’s control panel it reverts back to the previous default printer.
Solution
To fix this problem we need to change device value in registry.
Open registry editor and locate the path
“HKEY_CURRENT_USER/ SOFTWARE/ MICROSOFT/ WINDOWS NT/ CURRENT VERSION/ WINDOWS”
On the right pane Change entry for Device that has winspool,Ne00; delete whatever printer there is in the entry and just leave winspool,Ne00.Close the registry editor and restart the windows explorer.
****************
Windows cannot load your profile because it may be corrupted. You may be logged in using a temporary User Profile
Windows cannot load your profile because it may be corrupted. You may be logged in using a temporary User Profile
Release
Windows XP, Windows 7
Problem
When we trying to boot the windows showing the error “The user profile service failed the login. User profile cannot be loaded.”
Solution
This issue may occur if the user profile folder was deleted manually. A profile folder that is manually deleted does not remove the Security Identifier (SID) from the profile list in the registry. For solving the above problem we used the third party utility called Reprofier.
Login with default login user account. Open the Reprofiler utility. Select the corrupted user profile and select assign as shown in figure.
And restart the machine
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Cannot access shared files and folders or browse computers
Cannot access shared files and folders or browse computers
Release
Windows XP
Problem
When we trying to access network shared folders or workgroup computers, showing the following one of the issues.
1. Cannot access shared files and folders or browse computers.
2. You cannot locate other computers in the workgroup.
3. Showing the error “Workgroup Name is not accessible. You may not have permission to use this network resource.”
Solution
The problem may occur due to the following cases
1. The Computer Browser service is not started on one or more computers in the workgroup.
2. NetBIOS over TCP/IP is enabled on one or more computers in the workgroup.
Recommended
Update windows XP service pack 3.
Method1:
Open the registry editor and locate the path as shown below
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\NetBt\Parameters.
On the right pane delete the following values if they are exists.
1.NodeType
2.DhcpNodeType
Restart the computer.
Method 2:
Run the Fixit Utility Microsoft Fix it 50135 available from Microsoft website.
Downloadlink:http://download.microsoft.com/download/8/1/A/81AD4B33-1946-41B5-8D55-9EEE085F0006/MicrosoftFixit50135.msi.
Method 3:
Type the command ncpa.cpl on command prompt. Right click on the Local Area Connection
And select properties. On general Tab select advanced option. Click the WINS Tab. Under Netbios Settings.
click Enable NetBIOS over TCP/IP. Apply ok and restart the PC.
Method 4:
Open the services option by typing the services.msc on command prompt. Locate the Browser services and try to start.
Method 5:
Type the command ncpa.cpl on command prompt. Right click on the Local Area Connection
And select properties. Select the General Tab, and select the File and Print Sharing for Microsoft Networks. Click Install.
Make sure that File and printer sharing services is blocked by windows firewall.
Method 6:
Apply the Fixit Utility Microsoft Fix it 50393 from Microsoft
Restart the computer.
Windows Cannot Load the Locally Stored Profile
Windows Cannot Load the Locally Stored Profile
Release
Windows xp
Problem
While logging User Name, it will come. if you give “ok” desktop will load without any icons And we cannot change any user settings .
Even if we made any changes that will not be saved .After Reboot the system , Our existing settings will be lose .
Solution
Create a New User Account:
To create a new User Account in Following Steps:
· Start computer in safe mode , and then restart the computer ,
- After power on system self test press “F8” key,
- On the Windows Advanced Options menu, use the ARROW keys to select Safe Mode, and then press ENTER.
- To select the operating system to start.
- Log on as Administrator.
- In Control Panel, click User Accounts.
- Create a new user account. Windows makes a new directory for the account in the Documents and Settings folder.
- Quit User Accounts and Reboot the system.
- Create User Account in Command line :
Syntax : net user /add [username password ]
e.g. # net user /add usd hcl123
user name :usd
Password : hcl123
Note: via command line created user is Limited user only.
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