Archive for the ‘CentOS’ Category

CentOS System Administration Essentials

CentOS System Administration Essentials

CentOS System Administration Essentials

The description of this book is “Become an efficient CentOS administrator by acquiring real-world knowledge of system setup and configuration” and the author, Andrew Mallett, has put together quite a collection of information in there to help you do just that.

Probably worth mentioning here is that this book is obviously designed for someone not only familiar with Linux in general, but also comfortable eough with CentOS to dispatch with the usual obligatory chapters dealing with installation, etc.. Yes, this information is surely aimed for someone who is. or has designs for being a Systems Administrator. As it happens, I am “one of those guys” so I’ll give you my thoughts on how well he did.

One of the interesting things about Linux is there are so many ways to do things and so many areas of focus. This means that this area of information that a system Administrator should know is pretty expansive and what *I* think a System Administrator should be an expert in is not necessarily what someone else may think. Well, up to a point. There are some real basics in there as well. One of those is using vi or vim and noodling around on the command line, and this is right where Mallett heads for in the beginning of the book and rightly so.

After running through some great tips you start to dive into some deep subject matter on Grub, filesystems, processes (all really important stuff). Yum (package management) and managing users are also important standards that are covered well, and then you start diverging a bit from what I would consider “must know” information into, really, the more interesting stuff of the book. You walk through LDAP auth, Nginx web servers and puppet configuration management. While those may not be essentials for your systems, it sure is nice to at least have a basic understanding, and the information here on them can get you up and running. And then lastly we go back into the last topic, security, which is also a “must know”.

I quite liked this book, especially the portion on Nginx, which I had not played with before. It was good information, easy to read and use and the examples worked. I also noted that much unlike some other similar books I have reviewed, this book is not so voluminous as to make it impractical to read through in an afternoon or so and you can do so and come away immediately with some practical and usable information. Again, the book “CentOS System Administration Essentials” by Andrew Mallett, is available from Packt Publishing for under $25 and is well worth it for all you budding (and maybe not so budding) System Administrators out there.

Sunday, February 1st, 2015

Le Sigh…

Last night a couple of my infrastructure VMs suffered some catastrophic problems due to an unexpected power issue. This brings a couple of notable postables to mind:

Make sure you backup even your development work. The 2 VMs that got corrupted for me were development VMs that I was testing software and configs on, therefor I reasoned that I really didn’t need to back them up. Well, I was wrong.

The second is how to mount an LVM partition from a rescued disk. I had to dig around, but this is the first time this has ever happened to me:

lvm vgscan -v
lvm vgchange -a y
lvm lvs –all
mount /dev/vgname/lvname /mnt/somewhere

Now off to see what all I can rescue from my configs and data πŸ™

Wednesday, December 11th, 2013

CentOS 6 Linux Server Cookbook

CentOS 6 Linux Server Cookbook

CentOS 6 Linux Server Cookbook

OH YEAH! Another book review, and one on one of my favorite Linux distributions too!

Pakt Pub contacted me to do a review on their new CentOS 6 book, and boy was I excited at the chance. First of all, I generally like Pakt Pub‘s books, and second I really dig CentOS! Even better is this is all about using CentOS as a server, and I just happen to use quite a lot of CentOS as my preferred home server platform. And why, you may ask? Well, it very closely mirrors another enterprise level Linux that I use heavily in my professional environment. It’s good stuff.

I found this book particularly reminiscent of a few books I studied from to get my RedHat certs. There is a good bit of material in there – most things that a budging server administrator would want to know how to do, and it is formatted in a “recipe” format, which makes it fairly easy for readers to piece mail through if they are looking to do something specific in a hurry. I really like that kind of format because, lets face it, most of us have precious little time these days and reading line by line though technical materials is not usually high on our lists of things to spend our time on. Thankfully, as I said before, it’s easy to get to pertinent info here, and the writing is not really too dry or overly technical to begin with.

The book starts right out where it should by helping you not only download CentOS (for free of course), but also gives you example and instruction on several different installation methods. This is particularly useful for more advanced users because there are significant time savers to be had by using minimal and text method installs that most Linux books leave out. From there we are off to recipes for basic configuration changes like changing SELinux, IP addresses, time zone settings and the like. This is followed by a bunch of basic administrative info like using cron, starting services, package management and helping to secure your environment, before really focusing on what I like to refer to as the big 5 applications: Samba, Bind, MySQL, Mail and Apache. These are all covered in their own chapters, giving them plenty of room to address common specific topics and options. The only thing I found at all out of place is the last chapter which deals with FTP. I might be a little jilted here but it has been my experience that ftp usage is being deprecated in most places. But for those of you who do actually use it, this book covers setting up and using VSFTP, which can be daunting to get going without a little well written help, which this chapter *does* provide.

All in all, I find this a well written book covering what most system admins would really be looking for info on. In fact, this is one I really wish they had sent me in a paper edition so I could more easily loan it around to friends and coworkers whom, I am sure would find it helpful! At only $25.50 for the digital edition it would be silly for anyone new or unfamiliar with CentOS not to grab a copy before diving in. It will surely save you some time and aggravation and provide you with a good reference for future service additions and changes. It gets a nice thumbs up from me!

CentOS 6 Linux Server Cookbook

Tuesday, May 28th, 2013

Adventures in Virtualization

A long long time ago, I virtualized all my home infrastructure onto an ESXi 4.0 server. It has run perfectly fine, minus one hard drive failure, for quite a few years. Lately, though, I had been wanting to upgrade it because it’s not terribly fast and I have run out of resources to be able to add new VMs. It was running on a dual cpu machine (single core) with 160Gb HDD and 4Gb of ram, and I was just using it all up. No more ram for new stuff.

I decided that I would upgrade the matching spare server I had and try out KVM because I had used it a bit for RedHat training and it worked so well. Of course, Fessenden’s law, as opposed to Murphy’s law, stated simply that “Something will go wrong.” And it did. Over and over again.

First off, let me say that on an enterprise class server system, if it says it needs registered ECC ram, it is NOT kidding. I must have swapped ram around in that server 50 times before I noticed 2 sticks of non-registered ram in there. Once I got over that, I had 8Gb of ram and a new 250Gb HDD and I was ready to rock! Or so I thought.

I decided to use CentOS 6 as my virtualization host OS and that went right on but I soon discovered that my CPU doesn’t support virtualization. Ugh. So I decided that I would switch gears and go with virtualbox instead so that I could continue using my current hardware. I have often used virtualbox on other machines and it is a fantastic platform. I set about getting things running.

When I installed the base OS, I did a minimal install. No GUI, etc.. There is no sense in putting stuff on there you don’t need on a server right? Well, the very first thing I found was that I could not use the virtualbox gui controls because I did not have any X installed. To rectify that:

yum -y install xorg-x11-xauth dejavu-lgc-sans-fonts

You need the auth to be able to forward your X session, and need the fonts to be able to actually see words on your app.

Next I copied all my vmdk files to the new server. This takes a LONG time for old servers to move around 100Gb. Once there, however, I discovered that virtualbox cannot read native vmdk files. Ugh again.

yum -y install qemu-kvm

And then I could convert the vmdks to raw images, and then again to native vdi files for virtualbox.

qemu-img convert machine-flat.vmdk machine.bin
vboxmanage convertfromraw --format VDI machine.bin machine.vdi

I put all my machines together and noticed that virtualbox was complaining about uuid on some of the disk images. To fix that:

vboxmanage internalcommands sethduuid machine.vdi

The first machine I started up was a CentOS 6 machine and that fired right up, however, udev immediately reassigned my ethernet device to eth1. In order to get thatr back where it was supposed to be I had to go into /etc/udev/rules.d/70-persistent-net.rules and delete the ethernet rules in there and reboot.

Along about this time my server powered off. No idea why. It powered itself back on again about 30 seconds later. I checked everything on the server and it looked fine. Curious, but I kept on going.

Next I tried to start up my remaining Centos 5 VMs. These were problematic. The very first thing I noticed here was that they were barking because I never uninstalled the vmware drivers. I fired them back up on the original server and ran the program. I turned them back off and spent hours re copying the over, and then reformatting the vmdk files into vdi.

Starting them back up, I found that, again, they would not run. This time I received the error that it could not locate any LVM partitions. This, it turns out, is because the initrc files did not have the appropriate drivers in them. Fixing this was fun. First off, you need to add a cdrom drive to the vm and put a CentOS rescue cd/dvd there. Boot it up in rescue mode, chroot to the /mnt/sysimage and then fix the /etc/modprobe.conf file:

alias scsi_hostadapter mptbase
#alias scsi_hostadapter1 mptspi
#alias scsi_hostadapter2 ata_piix
alias scsi_hostadapter1 mptscsih
alias scsi_hostadapter2 mptscsih

The entries with the #s are the ones I had to change. Then I needed to rebuild all of the initrd images.

cd /boot
for file in $(ls init* | cut -d'-' -f2,3 | cut -d'.' -f1-6); do mkinitrd -v -f /boot/initrd-$file.img $file; done

After that, the machines came right up! Of course, the host powered right off. Several times over the next day. Grrr.

I figured that there was a hardware issue with the host somewhere and resolved to buy myself a new server. I picked an open box refurb from microcenter that had 8Gb ram, a 750Gb HDD and a nice quad core cpu that supported virtualization. Wohoo! I can now switch to KVM!

I set up the new machine and installed KVM and started copying vmdk files over again and, bingo, kernel panic. I rebooted and the machine would not even get past bios. This went on for a couple days until I took the machine back to microcenter. I picked up a different machine, better quad core with 12Gb of ram and 1Tb HDD and set about getting it running.

This time, success! I set up CentOS 6 and KVM, added the bridged networking and copied over the vmdk files. KVM will read vmdk files but I decided to convert to a more native format, qcow2, the preferred format for qemu, anyhow. that is fairly simple to do.

qemu-img convert -O qcow2 machine-flat.vmdk machine.qcow2

I put all the machines back together again and started them back up. I still had to do the initrd fixes on the CentOS 5 VMs to get them going, but after that all has been running fantastically!

Somewhere along the line here I figured out that my issue with my secondary server powering off was a bad port on my UPS.

KVM is really easy to run and manage for a Linux geek as opposed to VMware 4. The native gui tools do the job just fine, although they are not quite as intuitive to me as VMWare’s VIC. I am quite happy, though, with the switch. I now have more than twice the resources of my initial virtualization environment. Now I am good to go for several more test VMs and the new machine is nice and quiet and doesn’t have to hide under my couch πŸ™‚

Sunday, August 5th, 2012

PHP and stuff

Lately I have been working so hard that I haven’t even had any desire to do any fun computering at home. Today that changed a bit.

I decided this morning that it was high time I upgraded my all time favorite rss feed reader, tiny tiny rss. Well, wouldn’t you know it, after I did the install I found it required a version of php higher than I had available on my server. Time to upgrade.

I run Centos 5 on my main server and, by default, that carries a php 5.1.x. I needed 5.2 or greater. As it happens, php 5.3 is available in the repos, so I did the upgrade. For the uninitiated, that entails doing a “yum list installed | grep php”, which gives you a list of what you *have* installed. Next you remove php by doing “yum remove <and name all the packages in the prior list here>”. This, followed by “yum install <list of files for php 5.3>”. For example, I had php-common.i386 and php.i386 installed, so I did a “yum remove php-common php” and then “yum install php53-common php53” to get all my php 5.3 packages on there. This was followed by a quick “service httpd restart” to make sure my webserver was using the new version.

Murphy’s law states that “something will go wrong if it can”. Well, *MY* law states that “something will go wrong”, and it did. As it turns out, I had built a whole bunch of php applications maybe 7 years ago that my wife uses almost daily. In the olden days of php, you could declare a php script at the top by doing a “<?”. NOW, you need to declare it by doing “<?php”. Consequently, nothing I had written worked. It only took me a minute or two to identify why the problem was occurring, but fixing it was another story.

So, how do you find all the files you have to fix? Well, I used the “grep” command. More specifically, egrep. I went to my html root directory and searched by doing “egrep -r “<\?” * | egrep -vi “<\?php” | egrep -vi “<\?xml” | grep -v inary”. What does all that do? The first stanza looks recursively through the directory structure at every file and outputs the ones that have any “<?”‘s in them. The second takes that output but does NOT pass through any that are “<?php”. Why, because they would already be ok! The third takes the results and doesn’t pass through any that contain “<?xml”. The last one doesn’t pass through results from binary files. The end result is I had a list of directory / file / line information of all the files I had to change / update. A few minutes later, after using vim, the best text editor around, I was back up and running!

Saturday, July 14th, 2012

CentOS 6.2 WOW!

CentOS 6.2

This week I am helping out my Mother, who has just had knee replacement surgery, so, oddly enough, I actually have a small bit of time to actually post something here again!

Right before I left, I decided I wanted to press an old Dell laptop into service for giggles. It is a Dell Latitude D810, which has a 2.mumble Ghz processor, 60 or 80Gb hdd and 1.5 Gb of ram (I confess I did upgrade that a bit from 1Gb). The really great thing about this particular laptop is it has a 1900×1200 resolution on it’s 15.4 inch screen. This makes for a great work laptop because it has so much screen realestate.

Well, what to run on this machine? It originally came with Windows XP, but, as you can imagine, I just cannot see fit to run Windows on my laptops, so which Linux? I decided on trying CentOS. Specifically CentOS 6.2 i386, which is current as of this writing. As it turns out, that was a really great choice!

The CentOS install was exactly what I had come to expect from it, short and sweet. The only issue of note is an error you get about half way through that says “insufficient memory to start Kdump” or some such thing. This is really nothing to worry about and can be safely ignored. Other than that, after a reboot from the installer, the system was ready to rock-n-roll. As in completely! Everything was working. I had sound, wireless, X, you name it! No muss, no fuss. To me this was wonderful as the last time I put CentOS on a laptop, I had to mess around a little bit to get wireless going. This time I ended up in luck because apparently my Intel Corporation PRO/Wireless 2915ABG is completely supported out of the box. Woot!

Anyhow, I ended up following my own recommendations I blogged about earlier here to get all my required softwares going like I prefer. The only noteable there is that, apparently, the EPEL repo (that’s Extra Packages for Enterprise Linux for those in the know) has changed the URL to:

Also of note, I seemed to have a bit of trouble getting dropbox on here. The solution was to NOT use the dropbox package available in the repos, but to go directly to dropbox and download the package available for Fedora, which worked just fine.

Once all that was done, this old laptop worked WONDERFULLY, and, in fact, I am typing and working on it now.

Often I hear people say things like “get more use out of your old computer with Linux”, and, while this is certainly true, I tend to discourage that because running a modern operating system like Linux on older hardware can many times give the wrong impression. Things run slow and laggy and often that is interpreted as being Linux’s fault, when, in fact, you are just trying to shoehorn it on to your old 486. You REALLY get a superior Linux experience when running it on modern hardware and it becomes VERY easy to contrast it then to other modern operating systems. At any rate, I wanted to say that this is NOT the case here. Linux on this older hardware runs so phenomenally well that I am seriously inclined to recommend purchasing this particular laptop used for persons looking for an inexpensive but capable mobile computing environment. I see them listed on ebay and amazon for very close to $200, which is, in my opinion, quite a bargain compared to the performance I experience from my much newer and more expensive netbook.

In conclusion, I would have to say, don’t discount older hardware, and certainly don’t discount CentOS as a viable, capable and speedy desktop (yes I did say desktop) Linux distribution!

Monday, May 21st, 2012

Who is that masked man?

Probably you have either listened to me or read my thoughts or both for several years now, but it occurred to me today that someone out there might be interested in seeing what actually drives the LincGeek.

I currently live in Pennsylvania, but I was born and raised in Upstate NY, with a brief stint in Washington state. New Yorkers and hillbillies are my people and I understand them. Washington is some of the most beautiful country I ever spent time in and I hope to at least visit out there again someday.

Well, first and foremost, computers and Linux are my personal crack. I started on a life long obsession with computers back in 1983 with my first Vic=20 (Thank you William Shatner). I learned to program in BASIC and from there it was all over until I met Linux in the 90s, then that added into the mix.

I like the fastest computers I can get my hands on. I like Apple computers (more for their quality and aesthetics than OS – they do tend to run Linux very well). I love my Kindle, my Android phone and my Asus TF300T Linux Mint is probably the nicest version of Linux I have ever run and I use that almost exclusively as my desktop OS of choice. I am RedHat certified and use RHEL and CentOS for the vast majority of my enterprise and personal server needs, because, IMHO, it’s better than the rest.

I am a music lover. I dig 50s, 60s, 70s, 80s, Big Band, Jazz, Funk, Disco, Bluegrass and Classical music. I was a hardcore low brass musician and vocalist in my school years, even making it into “Who’s Who In Music” in my senior year in high school, and those are some of my most cherished and fondest memories. Rap is *NOT* music, by the way.

I have been married once, to my college sweetheart, for almost 20 years now and have an adult (she thinks so at least) daughter, currently in college. I am a Conservative Libertarian, politically, and a proud Christian.

Although I am now diabetic and stick mostly to various forms of Chicken and veggies, I LOVE good food. my favorites are good Irish cooking like my Grandma used to make. Corned Beef and Cabbage. And she made a monster macaroni and cheese too. I would literally hurt someone for some of that again. I strongly believe that vegetables are what food eats.

I like my coffee with (nonfat) milk and sweet-n-low. Buy it from Wawa because Starbucks coffee is overpriced and bitter yuppie coffie IMHO. I like an occasional good cigar (Acid Blondie) and enjoy them most when I can smoke them and hang out with my friends. (Edit, I am a confirmed Vaper now – RY4 absolutely ROCKS!)

I am not a drinker. If and when I do imbibe, I do so with Scotch or Whiskey as I believe beer must be what urine tastes like.

As you can probably surmise, I am highly opinionated, and as I have a monster sized guilty conscience and I am not at all politically correct, so if you ask my opinion, you are liable to actually get it.

I still think the occasional fart joke is funny. I hate unproductive meetings and long phone conversations. I try very hard to be honest, forthright, fair and maintain integrity.

I am a pet guy and love small furry mammals of all kinds. I have and have had cats, dogs, rabbits, mice, rats, ferrets and even a smattering of budgies and small lizards.

And now you know all about me!

Tuesday, February 7th, 2012

Transmission on RHEL/CentOS/Scientific Linux 6

I had a friend a few weeks ago who asked me for help getting the Transmission bittorrent client working on CentOS 6. I took these notes then and am sharing them now.

cd /etc/yum.repos.d/
NOTE: RHEL/CentOS 6 x86_64 users have to replace $arch with $basearch in the repo file
yum install transmission transmission-gtk

Wednesday, December 7th, 2011

CentOS 6 Desktop

CentOS 6

I love love RHEL and CentOS on servers but surprisingly, CentOS 6 makes a nice desktop as well! Here are some notes I took getting things going the way I like on my CentOS laptop.

Where I work, if you push your machine name to DHCP, it will register with DNS as well. This is a nice feature if you are in the habbit of ssh-ing to your boxes like I am. In order to accomplish this task, you change a setting in the dhclient.conf file, which for a long time has been found in /etc/dhcp or /etc/dhcp3. Well, things have been moved around a bit and it’s now located in /etc and the filename is dhclient-eth0.conf where eth0 is the interface you are using. My suspicion is that this was done to frustrate the 5 people in the world like myself who actually use this πŸ™‚

I really have no need for SELinux on this machine and therefor turn it off to keep it out of my way. This is easily accomplished by editing the /etc/selinux/config file and setting SELINUX=disabled. (then performing a reboot)

I also have no use for the default firewall ruleset. I normally do a chkconfig iptables off && service iptables stop and just address my firewall concerns later on.

What I *DO* need, often, if not always, are the development tools. Things like compilers and make, etc.. Get them by doing yum -y groupinstall “Development tools”.

Install the EPEL repo:
rpm -Uvh
rpm -Uvh
depending on your archetecture.

Gotta have clusterssh. If you don’t use it you should!
yum -y install clusterssh

I also must have my chrome web browser:
Install chrome from website

And Thunderbird too!
install thunderbird from website

Add the RPMForge repository:
rpm –import
rpm -Uvh
rpm -Uvh
depending on your archectecture.

And, lastly, if you are somewhere where this is legal, you can install all the codecs that make using your computer nice!
yum -y install compat-libstdc++-33 libdvdcss libdvdread libdvdplay libdvdnav lsdvd libquicktime flash-plugin mplayerplug-in mplayer mplayer-gui gstreamer-ffmpeg gstreamer-plugins-bad gstreamer-plugins-ugly
wget (or x86_64)
rpm -ivh mplayer-codecs-20061022-1.i386.rpm (or x86_64)
wget (or x86_64)
rpm -ivh mplayer-codecs-extra-20061022-1.i386.rpm (or x86_64)

Wednesday, December 7th, 2011

twidge on CentOS

A couple days ago I was reading a post from Knightwise and he mentioned using twidge on his server to do some fun stuff with his twitter account. Well! That sounded to me like just the thing for me to get some use from my neglected twitter account. Unfortunately, twidge is really best used on a debian type system and *my* server runs CentOS 5. This is a simple recipe to shoehorn twidge onto a CentOS 5 server.

I downloaded the twidge binary from

The binary requires libcurl-gnutls which CentOS just doesn’t have. I snuck around that by doing

ln -s /usr/lib/ /usr/lib/

Then the binary told me it needed libffi. This I could get from the epel repository. Do that by doing

rpm -Uvh

and then

yum install libffi

That gets twidge working ….. mostly. Because of the sneaky I pulled with that libcurl-gnutls thing, twidge generates an error message on each run. It still works fine, but gives me a message on each run:

twidge: /usr/lib/ no version information available (required by bin/twidge)

Undaunted, the easy fix for that is to dump the unneeded error to /dev/null like so

twidge lsrecent 2> /dev/null

And there you have it! For those of you looking to employ twidge on CentOS or similar Linux, this will get you going pretty quickly. Enjoy and I’ll tweet ya later!

Thursday, July 28th, 2011