Accessing OMD unter CentOS and Selinux

If you've got the error like this

OMD: Site Not Started

You need to start this site in order to access the web interface.


in your fresh configured and started OMD site, Selinux can cause the issue. Consider to configure Selinux properly (have a lot of fun!) or disable it in /etc/syssconfig/selinux.

CentOS and Active Directory 2008

This article is intended for those of you, who has read my old post about CentOS and the integration into Microsoft Active Directory. In my old post I referred to Microsoft Active Directory 2003. In cases, when you upgraded to MS AD 2008, you have to update some entries in configuration file /etc/nslcd.conf.

Yum's additional tools

I've learnt new helpful commands recently that belongs to yum tools (thank you MLLR). I'd like to say a few words about the usage of the commands.

OMD fails to start after CentOS upgrade to 6.4

I faced a problem starting OMD 0.54 after upgrading CentOS to the version 6.4. The start script returns a bunch of error messages:


[root@omd ~]# omd restart mysite
Doing 'restart' on site mysite:
Creating temporary filesystem /omd/sites/mysite/tmp...mount: can't find /omd/sites/                         mysite/tmp in /etc/fstab or /etc/mtab
ERROR
Removing Crontab...
Stopping xinetd...OK
Stopping icinga...Not running. OK
npcd was not running... could not stop
Stopping rrdcached...waiting for termination...OK
Stopping dedicated Apache for site mysite....OK
Starting dedicated Apache for site mysite...OK
Starting rrdcached...OK
Starting npcd...touch: cannot touch `/omd/sites/mysite/tmp/pnp4nagios/run/npcd.pid'                         : No such file or directory
chown: cannot access `/omd/sites/mysite/tmp/pnp4nagios/run/npcd.pid': No such file or directory
An Error occured while reading your config on line 197
Message was: "Could not open pidfile '/omd/sites/mysite/tmp/pnp4nagios/run/npcd.pid                         ': No such file or directory"
OK
/omd/sites/mysite/etc/rc.d/80-icinga: line 54: /omd/sites/mysite/tmp/nagios/nagios.cfg                         : No such file or directory
Icinga configuration file /omd/sites/mysite/tmp/nagios/nagios.cfg not found. Terminating...
Starting xinetd...OK
Initializing Crontab...OK

I found a couple of reports about the same problem. The root cause seems to be a bug (or a feature?) in the package util-linux-ng-2.17.2-12.9.el6.x86_64 that prevents non root users to mount partitions from /etc/fstab, whose path name conatains a symlink (symbolic link). In case of OMD /omd is a symlink pointing to /opt/omd.

A workaround that helped me to solve the problem was adding /opt to the appropriate path in /etc/fstab:

tmpfs                   /opt/omd/sites/nysite/tmp  tmpfs   noauto,user,mode=755,uid=mysite,gid=mysite 0 0

Upgrade Microsoft Hyper-V Linux IC from 3.3 to 3.4

Recently I had to upgrade the integration components on a lot of CentOS virtual systems running on a Hyper-V failover cluster. During the upgrade procedure I faced a couple of things, which I'd like you to be aware of. The version on the guest VM is CentOS 6.3, the Hyper-V failover cluster is running under Windows Server 2008 R2 SP1 and consists of 6 nodes.

Below is the output of LVM related commands before starting the upgrade of Linux IC:

Extending a LVM partition in a Hyper-V guest VM running CentOS

Imagine a scenario like the following: you have a Hyper-V host and a CentOS 6.3 guest. The CentOS guest has Microsoft Integration Services for Linux 3.3 installed and running. A data file system on the guest is running out of the free space:

[root@myhost ~]# df -h /data/svn/

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/data-svn   99G   93G  964M  99% /data/svn

Although the partition is a part of LVM, but your entire disk is almost full. In the article I'd like to show how you can get rid of this without getting your services offline.

Script to inform about new updates in CentOS

A couple days ago I shared my script for OpenSuSE. Now I've re-written that Perl script to speak the language of yum. The script below is intended to run periodically by cron and to send me an e-mail, if new updates have been found for the system. It's nothing extraordinary, yum-cron can this too. But an advantage of my Perl script is that the e-mail is sent only once. No email is sent, if the same updates are found again. The trick is that the Perl script saves the updates (if any) in a temporary file to compare its content then with the updates found at the current run.

Besides I wanted to see the installed and the available versions of a package side by side. I could unfortunately get this output with yum or repoquery directly.

CentOS 6.2 and Active Directory

In this article I’ll show you how to connect your CentOS to the Active Driectory as user backend. I assume that MSFU 3.5 (Microsoft Services For Unix) feature is activated in your AD.

There are a couple of tasks you have to do, when you’re going to bring your CentOS box with Active Directory. First of all, the nslcd daemon (nss-pam-ldapd) must be installed and configured. After that step you should be able to see UNIX specific attributes of users from AD backend. The next step is to setup authentication against AD.