Posts Tagged ‘CentOS’

EPEL NSD RPM and the missing PID file directory

Sunday, June 26th, 2011

NSD is a fantastic authoritative nameserver from NLnet Labs which was developed in conjunction with the RIPE NCC to be a highly scalable, secure authoritative nameserver which has no recursive features by design. In fact, it is such as good nameserver that it is used on three of the root namesevers (k.root-servers.net, h.root-servers.net and l.root-servers.net).

Thanks to the EPEL project run by the Fedora guys, you can quickly and easily install an up to date copy of NSD on CentOS/RHEL systems. The only problem that I have found so far is that the RPM doesn’t seem to create directory for the PID file specified in the /etc/nsd/nsd.conf and so the daemon won’t start out of the box.

Obviously it is easy enough to create the /var/run/nsd directory with mkdir, but remember to chown/chgrp this directory to the nsd user and group, otherwise and “nsdc restart” will fail with errors in /var/log/messages along the lines of “failed to unlink pidfile /var/run/nsd/nsd.pid: Permission denied“

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Posted in Red Hat and CentOS | No Comments »

Sysconfig ifcfg scripts and VLAN sub-interfaces

Monday, August 16th, 2010

If you are using the ifcfg scripts in /etc/sysconfig/network-scripts to bring up VLAN sub-interfaces on a NIC and you are getting messages such as:

Bringing up interface eth0.200: Device eth0.200 does not seem to be present, delaying initialization.

instead of

Bringing up interface eth0.200: Added VLAN with VID == 200 to IF -:eth0:-

as you would expect, then make sure that you have the vconfig RPM installed.

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Posted in Red Hat and CentOS | No Comments »

HyperVM and yum update Transaction Check Errors

Monday, August 16th, 2010

If you’re having file conflict problems when running “yum update” on servers with the lxlabsupdate repository for HyperVM (or Kloxo) installed then there’s a simple resolution:

cd /var/cache/yum/lxlabsupdate/packages/
rpm -Uvh *.rpm –replacefiles –replacepkgs

This should fix errors such as:

file /usr/share/man/man1/pcregrep.1.gz from install of pcre-8.02-1.el5_5.1.x86_64 conflicts with file from package pcre-6.6-2.el5_1.7.i386
file /usr/share/man/man1/pcretest.1.gz from install of pcre-8.02-1.el5_5.1.x86_64 conflicts with file from package pcre-6.6-2.el5_1.7.i386

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Intel VT Virtualisation Technology on Dell PowerEdge servers

Saturday, June 19th, 2010

Somewhat annoyingly, Dell seem to like to disable Intel’s VT (Virtualisation Technology, sometimes called VMX) in the BIOS on their Dell PowerEdge servers, which means that you can’t use the Xen hypervisor to virtualise Microsoft Windows Server without changing this setting, which requires a reboot of the server to take effect.
You can use omreport from the Dell OpenManage Server Administrator software to check whether or not you have Intel Virtualisation Technology enabled.
If you haven’t got OpenManaged Server Administrator installed, then you can enable the Dell yum repository for CentOS/Red Hat systems and install it with:

wget -q -O – http://linux.dell.com/repo/hardware/latest/bootstrap.cgi | bash
yum -y install srvadmin-base
/opt/dell/srvadmin/sbin/srvadmin-services.sh start

Once you’ve got the Dell OpenManage Server Administrator services running, you can take a look at what processor is installed in your system and what the current BIOS settings are with:

omreport chassis processors
omreport chassis biossetup

The two attributes that you’re looking for are Processor Virtualization Technology (which needs to be enabled) and Demand-Based Power Management (which needs to be disabled).

If you need to change them, then you can do this with:

omconfig chassis biossetup attribute=cpuvt setting=enabled
omconfig chassis biossetup attribute=dbs setting=disabled

Once that's done, then verify the new settings by running omreport chassis biossetup again and then once you’ve rebooted the server you can start taking advantage of the hardware virtualisation provided by Intel’s Virtualisation Technology.

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Posted in Red Hat and CentOS | No Comments »

Netcat saves the day!

Wednesday, June 2nd, 2010

During a botched upgrade taking an old CentOS box form 5.2 to 5.5, I ended up with a system in such a state that /lib/libselinux.so.1 and /lib64/libselinux.so.1 no longer existed. This is a major problem as it basically stops pretty much every program from working, you can’t even use cp or ls any more!

With yum and RPM unusable, SFTP/SCP/SSH clients and servers out of action and unable to use FTP or wget I thought this box was toast and was going to need a reboot and a live CD to bring it back to life.

After nosying around the system for a while to see what programs I could still run, I discovered that I could still run rsync, but this turned out to be little use as I couldn’t get RSH, SSH or RSYNC network connections in or out of the server.

The last thing I could think of was good old netcat, so I fired it up on another server with a known good copy of libselinux.so.1 and piped /lib64/libselinux.so.1 into it, then with everything crossed I piped it back out on the dying server, and lo and behold it worked and I was able to use ls again!

On the server (source) machine:

cat /lib64/libselinux.so.1 | nc -l 3333

On the client (destination) machine:

nc x.x.x.x 3333 > /lib64/libselinux.so.1

Where x.x.x.x is the IP address of the server.

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Posted in Red Hat and CentOS | 1 Comment »

Cancelled yum transactions

Saturday, May 22nd, 2010

If you’ve ever aborted a yum update for any reason, you’ve probably come across messages warning of transaction errors, such as the following example during an update from CentOS 5.4 to CentOS 5.5 that got cancelled part way through:

Transaction Check Error:
file /usr/include/libdevmapper.h from install of device-mapper-1.02.39-1.el5.i386 conflicts with file from package device-mapper-1.02.32-1.el5.x86_64
file /usr/share/man/man8/dmsetup.8.gz from install of device-mapper-1.02.39-1.el5.i386 conflicts with file from package device-mapper-1.02.32-1.el5.x86_64

Error Summary
————-

At the very start of the yum output, after “Resolving Dependencies” you should also see message saying

There are unfinished transactions remaining. You might consider running yum-complete-transaction first to finish them.
The program yum-complete-transaction is found in the yum-utils package..

This is nice and easy to resolve thankfully, you just need to use the suggested yum-complete-transaction utilit, which as the message suggests, can be found in the yum-utils package package.
This works just like the main yum program, except you don’t need to give it any arguments like install or update, you just run it and it will finish any incomplete transactions. hopefully this will fix any broken or cyclic dependancies where an update has been cancelled part way through.

I did find it somewhat ironic when I ran “yum install yum-utils” to gain access to the yum-complete-transaction command, I received the same message to install yum-complete-transaction via the yum-utils package, as that is exactly what I was trying to do!
Luckily, you can still install the yum-utils package from the normal system yum repositories whilst you have an outstanding transaction so you don’t have to mess around with downloading the RPM and installing it yourself.

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Posted in Red Hat and CentOS | No Comments »

Weirdest Linux command ever

Thursday, March 25th, 2010

This morning I had to run possibly the most bizzare Linux command ever whilst stripping down a CentOS server:

yum remove troursers

That really brightened up my day and made me smile. :)

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Posted in Red Hat and CentOS | No Comments »