HP T5630 - Thin Client Instrucciones de instalación y funcionamiento

Using the Enhanced Write Filter

HP Windows® XP Embedded-based thin clients:

t5630

t57x0

Abstract.............................................................................................................................................. 2

Introduction......................................................................................................................................... 2

Benefits of the Enhanced Write Filter...................................................................................................... 2

Enhanced Write Filter Status Service ...................................................................................................... 3

Enhanced Write Filter GUI.................................................................................................................... 4

EWF GUI Buttons ............................................................................................................................. 5

DOS Command-line Tool Boot Commands.............................................................................................. 5

Using Boot Commands ..................................................................................................................... 6

Abstract

This paper contains instructions for using the Enhanced Write Filter console application command-line

tool, the Enhanced Write Filter GUI and the Enhanced Write Filter status service.

Introduction

Windows XP Embedded includes the Enhanced Write Filter (EWF) console application command-line

tool, Ewfmgr.exe. In addition to the DOS command-line tool, the Windows XP Embedded image

includes an Enhanced Write Filter GUI. The EWF allows the operating system (OS) to boot from a

disk volume residing on any read-only media or write-protected hard drive while appearing to have

read/write access to the OS. The EWF saves all writes to another storage location called an overlay.

Changes made to the overlay will not be committed to the flash memory unless the EWF has been

disabled or the user performs an intentional commit.

The EWF manager console application can be used to issue a set of commands to the EWF driver,

report the status of each protected volume overlay and report the format of the overall EWF

configurations.

By including the EWF manager console application component in your configuration and building it

into your run-time image, you enable the use of Ewfmgr.exe and the corresponding commands.

Benefits of the Enhanced Write Filter

The EWF provides a secure environment for thin client computing. It does this by protecting the thin

client from undesired flash memory writes (flash memory is where the operating system and functional

software components reside). The write filter also extends the life of the thin client by preventing

excessive flash write activity. It gives the appearance of read-write access to the flash by employing a

cache to intercept all flash writes and returning success to the process that requested the I/O.

The intercepted flash writes stored in cache are available as long as the thin client remains active, but

will be lost when the thin client is rebooted or shut down. To preserve the results of writes to the

registry, favorites, cookies, and so forth, the contents of the cache can be transferred to the flash on

demand by the Altiris Deployment Solution software or manually using the Enhanced Write Filter

Manager.

After the write filter has been disabled, all future writes during the current boot session are written to

the flash, with no further caching until a reboot occurs. The write filter may also be enabled/disabled

through the command line. Always enable the writer filter after all of your permanent changes have

been successfully made.

The EWF is a powerful tool for any thin client environment in which multiple users have access to the

device. The EWF prevents unauthorized users from altering or damaging the image.

Enhanced Write Filter Status Service

This service creates an icon in the System Tray that shows the status of EWF. The EWF Status icon will

appear as a red “lock” when disabled, a green “lock” when enabled, and a yellow “lock” when the

state is set to change on the next boot.

Status Description Example

Red Disabled

Green Enabled

Yellow Commit Mode

Yellow with Red “X” Write Filter Corrupted

Important

In the event of a corrupted EWF state, you will need to re-flash the thin

client unit with the standard shipping image provided on the web.

If you are logged-on as Administrator, you can change the status of EWF by right-clicking on the icon

and selecting the desired EWF state.

Important

Since EWF Manager console utility (ewfmgr.exe) and the EWF status

service execute separate code, any status changes by ewfmgr.exe will not

be automatically reflected by the EWF status icon.

To refresh the status icon after modifying EWF through ewfmgr.exe, you must right-click on the icon

(you can then click anywhere on the screen to close the context menu). However, any operations

made through the EWF status icon menu will be visible through the EWF Manager console

application. Status and changes to the Enhanced Write Filter will be synchronized between the EWF

status icon and the EWF Manager Control Panel applet.

Enhanced Write Filter GUI

The EWF GUI can be accessed through the Control Panel or the Administrative Tools option for the

administrator.

To access the EWF GUI, perform the following steps:

1. Log in as an administrator.

2. Select Start > Control Panel > Other Control Panel Options or Start > Control Panel >

Performance and Maintenance > Administrative Tools.

3. Click the EWF Manager icon.

4. Use the EWF GUI to select the Write Filter options.

EWF GUI Buttons

The current version of the EWF GUI includes the following buttons:

Button Description

Enable EWF This button is the same as executing ewfmgr.exe c: -Enable from the DOS prompt.

Disable EWF This button is the same as executing ewfmgr.exe c: -Disable from the DOS prompt.

Overlay Configuration This button simply displays the Overlay information and is a combination of the information

supplied when executing ewfmgr.exe c: -Description and ewfmgr.exe c: -Gauge

from the DOS prompt.

Clear Boot Command This button is the same as executing ewfmgr.exe c: -NoCmd from the DOS prompt.

Commit Data to Volume This button is the same as executing ewfmgr.exe c: -Commit from the DOS prompt.

Note

When using the Commit boot command, all the temporary contents will be

permanently written to the flash memory. In addition, all content accessed

(and changes made) after running Commit, but before rebooting the

system, will be written to the flash memory as well. This includes changes

made during any number of login/logout sessions before the next reboot.

DOS Command-line Tool Boot Commands

The following table lists the EWF boot commands that are supported.

Boot Command Description

All Displays information about all protected volumes and performs a command, such as

disable, enable, and commit, on each volume if specified.

Commit Commits all current level data in the overlay to the protected volume, and resets the current

overlay level to 1 upon shutdown.

Disable Allows user to write to the image after the next reboot.

Enable Prevents the user from writing to the image after the next reboot.

Commitanddisable Combination of the Commit and Disable commands. This command will commit data in

the overlay upon shutdown. Additionally, EWF will be disabled after the system reboots.

Note

When using the Commit boot command, all the temporary contents will be

permanently written to the flash memory. In addition, all content accessed

(and changes made) after running Commit, but before rebooting the

system, will be written to the flash memory as well. This includes changes

made during any number of login/logout sessions before the next reboot.

Using Boot Commands

To use the EWF manager boot commands, type the following syntax in a command prompt:

EWFMGR <drive-letter> -[boot command].

Note

Because the EWF manager commands are executed on the next boot, you

must reboot the system for the command to take effect.

herein is subject to change without notice. The only warranties for HP products and

services are set forth in the express warranty statements accompanying such

products and services. Nothing herein should be construed as constituting an

additional warranty. HP shall not be liable for technical or editorial errors or

omissions contained herein.

indows is a trademark of Microsoft Corporation in the U.S. and other countries.

340317-005, July 2008

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