Archive for the ‘Windows Internals’ Category

PowerShell Script to raise Citrix Video Memory

Author: Remko Weijnen

28 Jan

On a Citrix XenApp 5 environment a user reported that he was unable to start a Full Screen session on a Dual Monitor Configuration.

He received this error message:

Citrix has a KB Article: “How to Allow More Memory for Session Graphics on Windows Server 2003” that explains exactly how we can solve this.

We need to change the MaxLVBMem registry value and we can use the Excel Sheet from the KB Article to calculate the proper value.

Please don’t set this value too high because a higher value means you will restrict other kernel memory pools.

You also need to deny the SYSTEM account the SetValue permission on the HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management key to prevent the Citrix IMA service from overwriting the new value.

So I wrote a small PowerShell script to change the permission and set the value:

$keyName = "SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\icawd\thin16"
$valueName = "MaxLVBMem"
# Calculate your value! http://support.citrix.com/article/CTX114497
[int]$value = 0xc00000

# Set Identity to SYSTEM via it's Well Known SID
[System.Security.Principal.SecurityIdentifier]$ident = "S-1-5-18"

# Open Registry Key (with Write Permissions)
$regKey = Get-Item "HKLM:"
$regKey = $regKey.OpenSubKey($keyName, $true)

# Fetch Existing permissions
$acl = $regKey.GetAccessControl()

# Construct a new Ace
$rights = [Enum]::Parse([Security.AccessControl.RegistryRights], "SetValue")
$deny = [Enum]::Parse([Security.AccessControl.AccessControlType], "Deny")
$rule = New-Object Security.AccessControl.RegistryAccessRule($ident, $rights, $deny)

# Add the new Ace to the Acl
$acl.AddAccessRule($rule)

# Apply the new Acl to the Registry key:
$regKey.SetAccessControl($acl)

# Now set the required Value
$regKey.SetValue($valueName, $value)

# Close the key
$regKey.Close()

$keyName = "SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\icawd\thin16"

$valueName = "MaxLVBMem"

# Calculate your value! http://support.citrix.com/article/CTX114497

[int]$value = 0xc00000

# Set Identity to SYSTEM via it's Well Known SID

[System.Security.Principal.SecurityIdentifier]$ident = "S-1-5-18"

# Open Registry Key (with Write Permissions)

$regKey = Get-Item "HKLM:"

$regKey = $regKey.OpenSubKey($keyName, $true)

# Fetch Existing permissions

$acl = $regKey.GetAccessControl()

# Construct a new Ace

$rights = [Enum]::Parse([Security.AccessControl.RegistryRights], "SetValue")

$deny = [Enum]::Parse([Security.AccessControl.AccessControlType], "Deny")

$rule = New-Object Security.AccessControl.RegistryAccessRule($ident, $rights, $deny)

# Add the new Ace to the Acl

$acl.AddAccessRule($rule)

# Apply the new Acl to the Registry key:

$regKey.SetAccessControl($acl)

# Now set the required Value

$regKey.SetValue($valueName, $value)

# Close the key

$regKey.Close()

1 Comment

Filed under: Citrix, PowerShell, script, Windows 2003, Windows Internals

Determine the System Page Size

Author: Remko Weijnen

24 Jan

Just a quick note: if you want to determine the page size of the OS (Windows) you can use the GetSystemInfo function.

Example:

var
  SystemInfo: SYSTEM_INFO;
  PageSize: DWORD;
begin
  GetSystemInfo(SystemInfo);
  PageSize := SystemInfo.dwPageSize;

var

SystemInfo: SYSTEM_INFO;

PageSize: DWORD;

begin

GetSystemInfo(SystemInfo);

PageSize := SystemInfo.dwPageSize;

Note that MSDN recommends to use the GetNativeSystemInfo function when running in a 32 bit app on an x64 OS (and you can use the IsWow64Process function to determine that).

One example where you need to know the PageSize is when you want to create a Paging File using the NtCreatePagingFile function because this function requires that the MinimumSize and MaximumSize parameters are a multiple of the PageSize.

Some interesting links on the subject:

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Filed under: Delphi, Windows Internals