Normaly you should always have backups of your databases, restoring suspected databases is not a good option, but I think at some point in time, in some situation you’ll want to do it anyway.
So today I set up a test case for this. I mirrored one of our database servers and made it crash, badly.
Two databases were corrupted, and went to the "suspect state".
MS SQL started throwing errors in our general direction like:

"Database cannot be opened. It has been marked SUSPECT by recovery."

Not good, but just what we wanted…

So how would it be possible to recover these databases?

First, set them to emergency mode, this way you will be able to retrieve control.
In emergency mode you can actually open the database:

alter database "test-database" set emergency;

Second, put them in single mode (needed for the check we will be performing):

alter database "test-database" set single_user;

Then, check the database (this repair allows data-loss, since I’m sure some data will have to be lost in my scenario):

dbcc checkdb (’test-database’, REPAIR_ALLOW_DATA_LOSS);

Finally, if the check succeeded, you can re-enter multi-mode:

alter database "test-database" set multi_user;

Et voila, the database is restored…
Not a best practice, but it may save some time once.

Greets,

Koen

If you want to configure a serial console on your Dell PE R410 (or R710) server with CentOS 5.4 (or 5.3 and probably also the Red Hat Enterprise systems) you can use these guidelines.
In the Bios:

Under "Serial Communication":
Serial Communication: On with Console Redirection via COM1
Serial Port Address: Serial Device1=COM2,Serial Device2=COM1
External Serial Connector: Serial Device2
Failsafe Baud Rate: 115200
Remote Terminal Type: VT100/VT220
Redirection After Boot: Enabled (so grub displays)

Then you configure Grub:

title CentOS (2.6.18-164.6.1.el5) Serial
        root (hd0,0)
        kernel /vmlinuz-2.6.18-164.6.1.el5 ro root=LABEL=/ console=tty0 console=ttyS0,115200n8
        initrd /initrd-2.6.18-164.6.1.el5.img

This makes the kernel display it’s messages on screen and over the serial console.

In /etc/securetty append:

ttyS0
ttyS1

This way root can log in using the serial console.

Finally configure the inittab (/etc/inittab) and add the following line:

co:2345:respawn:/sbin/agetty ttyS0 115200 linux

Now reboot and enjoy pure serial console goodness over ip (ipmi).

(Oh, don’t forget to enable IPMI over lan in the iDrac configuration and to set a username, password and ip-address.
The iDrac 6 configuration flashes by when the server boots.)

Kind regards,

Koen

When running through what should be a simple and painless Microsoft Sharepoint installation on a Windows Server 2003 (with IIS6 pre-installed), I encountered the following problem:

Server Error in ‘/_layouts’ Application.

IIS is kind enough to hide all the information about the error, so there you are, without a clue.
Maybe this can solved in the "SharePoint Central Administration"? No luck either, now it throws a similar error.
So, to resolve this issue, we first need to activate the error output in the web.config.
This is located at the following location:

C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\template\admin\1033\web.config

Open the file using your favourite text editor and search for the line which sets the customErrors (line 3), change it to:

<customErrors mode="RemoteOnly" />

Now you’ll be able to view the errors when browsing to your Sharepoint installation from the server itself.
This time it presents you the real problem:

Parser Error Message: Could not load file or assembly ‘System.EnterpriseServices, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’ or one of its dependencies. The system cannot find the file specified.

Assembly Load Trace: The following information can be helpful to determine why the assembly ‘System.EnterpriseServices, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’ could not be loaded.

So, how do we fix this missing assembly?
Open two windows explorer screens with these locations:

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727
C:\WINDOWS\assembly

(The .NET Framework version and Windows Path may differ depending on your installation.)

Then drag the file "System.EnterpriseServices.dll" from the Microsoft.NET\Framework\v2.0.50727 folder to the assembly folder.

Now the problem should be fixed. (It is possible you’ll have to recycle the Application Pool.)
Reload your browser windows, both the Central Administration page at port 9503 en the normal sharepoint pages at port 80 should work.

Thanks goes out to the people at forums.asp.net .

Kind regards,

Koen

yum clean all

Most likely yum is using some old cached information.
(We encountered this problem when upgrading from CentOS 5.0 to 5.3.)

We suggest drupal enabled website hosting customers to opt for a Virtual Private Server Light or even Virtual Private Server Standard setup. This means you can set up a nice isolated environment for a Drupal driven CMS website with dedicated server performance at severe reduced cost.

When setting up the environment be sure to run through the following checklist:

• CentOS 5.3 (for example)
• Apache 2.2 webserver
• MySQL 5.0 database server
• PHP 5.1 or even better, 5.2
• and, very important: eAccelerator 9.5.3 or higher.

Why the eAccelerator? Well Drupal uses a lot of cached pages. Enabling Drupal caching already gives you a boost but installing eAccelerator makes sure frequently used php scripts are stored in a compiled state thus allow retrieval faster.

On top of that, you may optimize the MySQL query_caching settings, as they Drupal also uses a lot of the same queries.

You can find the latest version of eAccelerator here: http://eaccelerator.net/

Take care,

Dominique

However, after having migrated a Windows server, we observed that the attributes of folders on the filesystem had been modified.  In Windows Explorer, everything seemed all right, but when FTP’ing to certain folders, or when viewing them with the ‘dir’ command, the folder were hidden.  It appeared that the ’system’ attribute had been set throughout the C drive.

We solved the problem by executing

attrib /S /D -S -H -R

Cheers,

Denis

I thought it would be good to share this simple command to regenerate SSH keys:

rm -fr /etc/ssh/*key*
service sshd restart
(Please be careful when executing this command, it will remove files without confirmation!)

In normal situations you would never need this…
However it can be usefull when cloning machines.

Greets,

Koen

 service snmpd start
Starting snmpd: /usr/sbin/snmpd: symbol lookup error: /usr/lib/libnetsnmpagent.so.10: undefined symbol: boot_DynaLoader
                                                           [FAILED]
 

Citrix knows of this problem, but for those who cannot wait for a fix, here’s a solution:

• Enable the CenOS yum repositories, in /etc/yum.repos.d/CentOS-Base.repo
• Remove the snmp packages and install the new CentOS packages:
  (for the sake of safety, keep a backup)
  • rpm -qa |grep snmp
    net-snmp-libs-5.3.1-19.3.xs361
    net-snmp-5.3.1-24.2.xs367
  • rpm -e –repackage net-snmp-5.3.1-24.2.xs367 net-snmp-libs-5.3.1-19.3.xs361
    warning: /etc/snmp/snmpd.conf saved as /etc/snmp/snmpd.conf.rpmsave
  • yum install net-snmp
  • service snmpd start

Your repackaged rpms are in /var/spool/repackage/ .
These packages can be reinstalled using:

rpm -i –nomd5 package.rpm

(Note: you need 2 hyphens before nomd5: - -nomd5)

Please keep in mind that deploying thirth party rpms and changing the domain controller (dom0) is not supported by Citrix!

This occured in a complex XenServer setup we were building.
When booting the (paravirtualised) guest we saw this message in the systems log:
kernel: drbd6: bio would need to, but cannot, be split: (vcnt=4,idx=0,size=4096,sector=4423615)

Simultaniously the guest would complain about unreadable sectors on the drive.

The issue is actually rather simple, and documented on the internet.
But while some xensource users switch over to file-based VM’s as a work-around, this is not an option in XenServer.

So, how can this really be solved?
By simply adding an extra parameter to the drbd.conf:

  disk {
    max-bio-bvecs 1;
  }

This simple switch effectively cures the whole situation.
If you want more information about this switch, please read the man files on drbd.conf

man drbd.conf

The switch and what it does is fairly well documented there.

Greets,

Koen

This can be done with these commands:

Windows: ipconfig /flushdns
Linux: /etc/init.d/nscd restart (or service nscd restart, or /etc/rc.d/init.d/nscd, depending on your distribution)
Mac OSX: dscacheutil -flushcache (or lookupd -flushcache for Tiger)

These commands should be entered in a terminal ("cmd.exe" for the Windows users).