When attempting to install Windows Server 2008 R2 under XEN, after loading from the disc, the installer will blue screen with the error:

STOP: 0x0000005D (<4 hex values, last 3 being 0x0000000000000000>)

To resolve this, try to enable pae in your XEN configuration file. ie, add the following line:

pae = 1

I am currently using the following configuration under XEN 3.12. Hopefully this will help.

kernel = '/usr/lib/xen/boot/hvmloader'
builder = 'hvm'
device_model = '/usr/lib64/xen/bin/qemu-dm'
maxmem = 4096
memory = 1024
vcpus=1
pae = 1
acpi=1
apic=1

name = "xenwin"

vif = [ 'type=ioemu' ]

disk = [ 'phy:/dev/VolGroup00/winserv08r2_disk,ioemu:hda,w',
         'file:/vm/iso/win2008server-r2.iso,ioemu:hdc:cdrom,r' ]

# Boot from the CD 
boot='d'

vnc=1
vncconsole=1
vncpasswd=''
sdl=0

stdvga=0 
serial='pty'
ne2000 = '0'
usbdevice='tablet'

on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'

Tested a school lab Sun v60x server with CentOS 5.5 loaded. It is a 1u full rack server and thus, uncomfortably loud.

Specs:
2x Xeon @ 3.06GHz
2GB Memory
2x 36GB 10k Disks

========================================================================
   BYTE UNIX Benchmarks (Version 5.1.2)

   System: server: GNU/Linux
   OS: GNU/Linux -- 2.6.18-194.el5 -- #1 SMP Fri Apr 2 14:58:35 EDT 2010
   Machine: i686 (i386)
   Language: en_US.utf8 (charmap="UTF-8", collate="UTF-8")
   CPU 0: Intel(R) Xeon(TM) CPU 3.06GHz (6113.9 bogomips)
          Hyper-Threading, MMX, Physical Address Ext
   CPU 1: Intel(R) Xeon(TM) CPU 3.06GHz (6112.7 bogomips)
          Hyper-Threading, MMX, Physical Address Ext
   CPU 2: Intel(R) Xeon(TM) CPU 3.06GHz (6112.8 bogomips)
          Hyper-Threading, MMX, Physical Address Ext
   CPU 3: Intel(R) Xeon(TM) CPU 3.06GHz (6112.8 bogomips)
          Hyper-Threading, MMX, Physical Address Ext
   08:16:31 up  2:58,  9 users,  load average: 0.02, 0.66, 0.73; runlevel

------------------------------------------------------------------------
Benchmark Run: Tue Oct 19 2010 08:16:31 - 08:44:46
4 CPUs in system; running 1 parallel copy of tests

Dhrystone 2 using register variables        5016443.2 lps   (10.0 s, 7 samples)
Double-Precision Whetstone                     1193.4 MWIPS (10.6 s, 7 samples)
Execl Throughput                               1798.0 lps   (29.8 s, 2 samples)
File Copy 1024 bufsize 2000 maxblocks        182385.5 KBps  (30.0 s, 2 samples)
File Copy 256 bufsize 500 maxblocks           52532.0 KBps  (30.0 s, 2 samples)
File Copy 4096 bufsize 8000 maxblocks        491880.2 KBps  (30.1 s, 2 samples)
Pipe Throughput                              328327.0 lps   (10.0 s, 7 samples)
Pipe-based Context Switching                  71385.9 lps   (10.0 s, 7 samples)
Process Creation                               6120.4 lps   (30.0 s, 2 samples)
Shell Scripts (1 concurrent)                   3269.1 lpm   (60.0 s, 2 samples)
Shell Scripts (8 concurrent)                    767.9 lpm   (60.0 s, 2 samples)
System Call Overhead                         410651.3 lps   (10.0 s, 7 samples)

System Benchmarks Index Values               BASELINE       RESULT    INDEX
Dhrystone 2 using register variables         116700.0    5016443.2    429.9
Double-Precision Whetstone                       55.0       1193.4    217.0
Execl Throughput                                 43.0       1798.0    418.1
File Copy 1024 bufsize 2000 maxblocks          3960.0     182385.5    460.6
File Copy 256 bufsize 500 maxblocks            1655.0      52532.0    317.4
File Copy 4096 bufsize 8000 maxblocks          5800.0     491880.2    848.1
Pipe Throughput                               12440.0     328327.0    263.9
Pipe-based Context Switching                   4000.0      71385.9    178.5
Process Creation                                126.0       6120.4    485.7
Shell Scripts (1 concurrent)                     42.4       3269.1    771.0
Shell Scripts (8 concurrent)                      6.0        767.9   1279.8
System Call Overhead                          15000.0     410651.3    273.8
                                                                   ========
System Benchmarks Index Score                                         419.7

------------------------------------------------------------------------
Benchmark Run: Tue Oct 19 2010 08:44:46 - 09:13:05
4 CPUs in system; running 4 parallel copies of tests

Dhrystone 2 using register variables       10913892.7 lps   (10.0 s, 7 samples)
Double-Precision Whetstone                     3875.1 MWIPS (10.4 s, 7 samples)
Execl Throughput                               4163.8 lps   (29.8 s, 2 samples)
File Copy 1024 bufsize 2000 maxblocks        119217.0 KBps  (30.1 s, 2 samples)
File Copy 256 bufsize 500 maxblocks           32092.8 KBps  (30.0 s, 2 samples)
File Copy 4096 bufsize 8000 maxblocks        364708.0 KBps  (30.1 s, 2 samples)
Pipe Throughput                              877013.1 lps   (10.0 s, 7 samples)
Pipe-based Context Switching                 251983.1 lps   (10.0 s, 7 samples)
Process Creation                              13102.1 lps   (30.0 s, 2 samples)
Shell Scripts (1 concurrent)                   5817.9 lpm   (60.0 s, 2 samples)
Shell Scripts (8 concurrent)                    820.7 lpm   (60.2 s, 2 samples)
System Call Overhead                        1060775.7 lps   (10.0 s, 7 samples)

System Benchmarks Index Values               BASELINE       RESULT    INDEX
Dhrystone 2 using register variables         116700.0   10913892.7    935.2
Double-Precision Whetstone                       55.0       3875.1    704.6
Execl Throughput                                 43.0       4163.8    968.3
File Copy 1024 bufsize 2000 maxblocks          3960.0     119217.0    301.1
File Copy 256 bufsize 500 maxblocks            1655.0      32092.8    193.9
File Copy 4096 bufsize 8000 maxblocks          5800.0     364708.0    628.8
Pipe Throughput                               12440.0     877013.1    705.0
Pipe-based Context Switching                   4000.0     251983.1    630.0
Process Creation                                126.0      13102.1   1039.9
Shell Scripts (1 concurrent)                     42.4       5817.9   1372.2
Shell Scripts (8 concurrent)                      6.0        820.7   1367.8
System Call Overhead                          15000.0    1060775.7    707.2
                                                                   ========
System Benchmarks Index Score                                         702.1

To disable the visual bell for the current screen instance, hit:

CTRL+A, CTRL+G

For a permanent fix, put the following into the ~/.screenrc file

vbell_msg "bell: window ~%" # Message for visual bell
vbellwait 2 # Seconds to pause the screen for visual bell
vbell off # Turns visual bell off

While I was trying to add a virtual disk to a headless virtual machine, upon running

VBoxManage modifyvm MachineName --hda DiskName.vdi

this error occurs:

ERROR: Could not find a storage controller named 'IDE Controller'

This can be resolved by replacing

<StorageControllers /> 

with

<StorageControllers>
  <StorageController name="IDE Controller" type="PIIX4" PortCount="2">
  </StorageController>
</StorageControllers>

Actually, scratch everything above. Use the following tutorial: http://forums.virtualbox.org/viewtopic.php?f=7&t=28273

If Sendmail takes several minutes to start, and your PHP scripts hangs when attempting to send emails via sendmail (eg: using the mail() function), ensure that your hosts file has its host name as an alias to localhost.

For instance, your hosts file should look something like this:

[leo@crow ~]$ cat /etc/hosts
127.0.0.1               localhost.localdomain localhost
109.169.59.122                     crow

You would want to add your host name to 127.0.0.1:

[leo@crow ~]$ cat /etc/hosts
127.0.0.1               localhost.localdomain localhost crow
109.169.59.122                     crow

Once that’s done, Sendmail should start and work normally.

The following is the unixbench benchmark ran on the XEN-PV Aquatic package offered at DamnVPS (ThrustVPS)

========================================================================
   BYTE UNIX Benchmarks (Version 5.1.2)

   System: crow: GNU/Linux
   OS: GNU/Linux -- 2.6.33.3 -- #1 SMP Thu May 13 22:30:34 BST 2010
   Machine: x86_64 (x86_64)
   Language: en_US.utf8 (charmap="UTF-8", collate="UTF-8")
   CPU 0: Intel(R) Xeon(R) CPU E5620 @ 2.40GHz (4788.0 bogomips)
          Hyper-Threading, x86-64, MMX, Physical Address Ext, SYSENTER/SYSEXIT, SYSCALL/SYSRET
   18:49:48 up  5:11,  2 users,  load average: 0.08, 0.02, 0.01; runlevel 3

------------------------------------------------------------------------
Benchmark Run: Fri Jul 30 2010 18:49:48 - 19:18:08
1 CPU in system; running 1 parallel copy of tests

Dhrystone 2 using register variables       14337184.0 lps   (10.0 s, 7 samples)
Double-Precision Whetstone                     2868.0 MWIPS (9.9 s, 7 samples)
Execl Throughput                               1545.8 lps   (29.9 s, 2 samples)
File Copy 1024 bufsize 2000 maxblocks        243675.8 KBps  (30.0 s, 2 samples)
File Copy 256 bufsize 500 maxblocks           62276.1 KBps  (30.0 s, 2 samples)
File Copy 4096 bufsize 8000 maxblocks        705056.0 KBps  (30.0 s, 2 samples)
Pipe Throughput                              363431.4 lps   (10.0 s, 7 samples)
Pipe-based Context Switching                  72559.7 lps   (10.0 s, 7 samples)
Process Creation                               3171.4 lps   (30.0 s, 2 samples)
Shell Scripts (1 concurrent)                   2853.2 lpm   (60.0 s, 2 samples)
Shell Scripts (8 concurrent)                    389.9 lpm   (60.1 s, 2 samples)
System Call Overhead                         421968.1 lps   (10.0 s, 7 samples)

System Benchmarks Index Values               BASELINE       RESULT    INDEX
Dhrystone 2 using register variables         116700.0   14337184.0   1228.6
Double-Precision Whetstone                       55.0       2868.0    521.5
Execl Throughput                                 43.0       1545.8    359.5
File Copy 1024 bufsize 2000 maxblocks          3960.0     243675.8    615.3
File Copy 256 bufsize 500 maxblocks            1655.0      62276.1    376.3
File Copy 4096 bufsize 8000 maxblocks          5800.0     705056.0   1215.6
Pipe Throughput                               12440.0     363431.4    292.1
Pipe-based Context Switching                   4000.0      72559.7    181.4
Process Creation                                126.0       3171.4    251.7
Shell Scripts (1 concurrent)                     42.4       2853.2    672.9
Shell Scripts (8 concurrent)                      6.0        389.9    649.8
System Call Overhead                          15000.0     421968.1    281.3
                                                                   ========
System Benchmarks Index Score                                         466.6