FreeBSD or Linux

FreeBSD or Linux (Ubuntu/RHEL)? This is a very old question. It’s like asking iPhone or Android. There is no short answer. It all depends on your situation. To make things easier, I am going to break it down into six simple questions to help you making decision.

My Background
I have been a FreeBSD user since 2003. My usage on FreeBSD mainly on service-oriented stuffs such as web farm, database clusters and file system etc. In short, I mainly use my FreeBSD system via command line. In 2009, I jumped into Linux world (Ubuntu/RHEL) because of my job. As an advanced user on both Operating Systems (FreeBSD and Ubuntu/RHEL Linux), here is my guide on these two systems.

There is only one FreeBSD, but there are many different variants of Linux. The Linux I mention below refers to two popular distributions: RHEL and Ubuntu.

FreeBSD vs Linux: Q.1 How do you describe yourself?

I am a very demanding person. I like to control everything I manage. –> FreeBSD
I don’t care about how a system is run. I am okay as long as it just works. –> Linux / Ubuntu / RHEL

Comment:
FreeBSD gives you freedom to control every single thing. One of its coolest feature is the port tree. You can build every application from source using port tree. In Linux world, you usually install applications from pre-built/pre-compiled package (yum, apt-get etc), which may not be exactly what you need.

Example:
In RHEL and Ubuntu, HTTP load balancer module does not come with Apache by default. You will need to compile Apache from source. What about in FreeBSD? All you need is to check a box (pretty much like shopping cart) and you are done.

FreeBSD vs Linux: Q.2 Do you prefer Ferrari or Hyundai?

Ferrari / BMW / SLR Camera –> FreeBSD
Toyota / Hyundai / Point and Shoot Camera / Phone Camera –> Linux / Ubuntu / RHEL

Comment:
The technology uses by FreeBSD such as kernel, file system, architecture etc are way better and more advanced than Linux. It’s like comparing Ferrari and Hyundai (And no, I am not kidding).

Example 1:
I need to run some extreme applications (e.g., DNA Sequence Alignment) which use all available threads and memory. The default settings of memory management in Linux is very poor. Every time I run my application, the system becomes not usable to other users. However, FreeBSD does not have this server problem. In fact, FreeBSD is smart enough not to cause the system to freeze. Of course you can tweak the memory management settings in Linux, or even run the command along with the nice command. However, these settings are just not available out of the box, and most of the time, you learn these tricks after your system has problem.

Example 2:
I installed FreeBSD 11 and RHEL 7 on two identical computers respectively. Both use default settings and enable similar services, such as enabling the SSH server and disable booting to X-Windows (RHEL). I used these two machines for exact the same purposes: SSH tunneling, with exact the same work load (evenly distributed). After using them for a month, I checked the memory usage. With FreeBSD, the available memory is about 800MB (out of 1GB), while there are only 200MB left (out of 1GB) on RHEL. Yes, Linux (at least with RHEL 7) consumes lots of memory.

Example 3:
FreeBSD comes with ZFS (The next generation file system) by default. Although it has been ported to Linux world, it is definitely unstable. We’ve tried to use it in a production environment. One thing that we’ve learned is that the ZFS may stop working after upgrading to a newer Linux kernel. I’ve received countless of email alert about missing the files (ZFS is not working, of course the files are gone) in the middle of the night. I ended up disable the auto update and disable the reboot after the update. Sounds familiar? That’s a feature in Windows, and for some odd reasons, this feature is available in Linux, a server.

Example 4:
LVM+RAID is an the most advanced storage method in Linux world. Unfortunately it does not do what it promises, i.e., you may lose your data if a hard drive is failure, even if you follow its directions to detach your failed hard drive correctly. Not to mention that the data will get corrupted if the power is down (which has been taken care of in ZFS, available in FreeBSD).

That’s why I prefer ZFS over LVM+RAID here: Building a Super Large and Reliable File Server with Mixed Size of Harddisks. It solves my problem (yes, even the power is failed during writing to the disk, my data is still safe!)

FreeBSD vs Linux: Q.3 Do you have lots of free time?

Yes: FreeBSD
No: Linux / Ubuntu / RHEL

Comment:
Making a production-ready system using FreeBSD can take you days to weeks if you are not an experienced FreeBSD user, while everything works out of the box in Linux. Sometimes, the new upgrade from the port tree can drive you nut, such as package conflicts etc. However, working with Linux is a leisure thing.

Example:
Installing Apache + MySQL + PHP from FreeBSD port (compiling the source) can take at least half day on a computer with a dual core CPU (AMD Athlon 64 X2 Dual Core Processor 4600+), while it takes less than 30 minutes on Linux. That’s because you need to compile the code from source in FreeBSD, while you simply download the packages and extract them in Linux. The time difference is huge.

FreeBSD vs Linux: Q.4 Do you prefer simplicity or complexity?

Adding sugar into water –> FreeBSD
Taking sugar away from soda–> Linux / Ubuntu / RHEL

Comment:
FreeBSD is a very very simple system. Think of it as a bare-bone system that comes with no junk. By default, it comes with no graphic user interface, no unnecessary application. It likes a pure distilled water.

In Ubuntu / RHEL, everything is configured and ready to use. It comes with very attractive, beautiful graphical user interface. Everything just works out of the box, no tuning or tweaking is required. However, it also comes with lots of junk such as Ubuntu One (For Ubuntu Cloud service), SELinux (A program developed by Red Hat where many people don’t use it), etc. It makes your system very bulky and increase the computation resource consumption.

FreeBSD vs Linux: Q.5 Are you going to use the computer as desktop?

Yes: Linux / Ubuntu / RHEL
No: FreeBSD

Comment:
Setting up a desktop-ready system on FreeBSD can take a long time. Main reason is the drivers availability. A lot of hardware such as graphic cards, audio cards or webcams are not supported in FreeBSD natively. If you want to get them working as good as on Windows / Ubuntu, you will need to get the driver first (if available), build it (which may gives error during compiling the codes), and recompile the kernel to make it supports the new driver, which can take few days if you are not experienced with FreeBSD and debugging driver.

On the other side, the Linux driver community is very strong and well developed. Usually they develop drivers for most popular hardware.

Example:

#1: My Logitech Orbit MP webcam (Pan / Tilt / Zoom) is not working on FreeBSD but works like a charm on Linux.

#2: Some vendors such as Highpoint may stop developing drivers for their products for newest version of FreeBSD.

FreeBSD vs Linux: Q.6 Do you need to blame someone when something goes wrong?

Yes: Linux / Ubuntu / RHEL
No: FreeBSD

Comment:

When something goes wrong, you can blame Linux and you can’t blame FreeBSD.

FreeBSD is a community driven operating system, while some Linux distributions such as Ubuntu and RHEL are backed by commercial vendors. In the world of FreeBSD, it is not uncommon that some unskilled developers introduce bugs, troubles to the rest of the world. Yes, we know it is free, so we can’t complaint about it. However, as an IT administrator, you will need to use your judgement to judge whether those new stuffs are safe to use or not. In short, that will increase your workload. It’s more like Windows update. How many people actually read the change log before hitting the update button?

In Linux (e.g., RHEL), that’s a whole different story. Every patches, new updates have been screened by the vendor before hitting to public. So you can trust them in some degree. And the key thing is, you can blame them when something goes wrong.

Conclusion

In short, use FreeBSD for your personal purpose while Linux for your work. Be the top 5%, not the bottom 95%.

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This tutorial is for Fedora Linux. If you are looking for setting up Pure-FTPd on FreeBSD, click here.

My client likes to send me a huge data file (More than 10GB after compressed). Since I don’t care about the security during the transfer, I decide to go with the old school technology: FTP.

Basically, I need to set up a FTP server with virtual user. In the other words, the log in used by the FTP server has nothing to do with my system login, and I can easily disable that at any time.

0.) Make sure port 21 is opened. You can update this setting in the Fedora Firewall settings.

1.) Install Pure-FTPd

sudo yum install pure-ftpd -y

2.) Create a user for Pure-FTPd, here I simply call it ftpuser.

sudo adduser ftpuser

3.) Let say, we want to create a user called guest to access the ftp server. guest is a virtual user, and its virtual home is in /home/ftpuser/guest

sudo mkdir /home/ftpuser/guest
sudo chown -R ftpuser:ftpuser  /home/ftpuser/
sudo chmod a+rw -R /home/ftpuser/

4.) Edit the Pure-FTPd configuration

sudo nano /etc/pure-ftpd/pure-ftpd.conf

5.) Uncomment the following:

PureDB                        /etc/pure-ftpd/pureftpd.pdb

6.) Start the Pure-FTPd

/etc/init.d/pure-ftpd start

If you want to start Pure-FTPd automatically, include this line in /etc/rc.local

7.) Create a user and add it into the Pure-FTPd database:

sudo pure-pw useradd guest -u ftpuser -d /home/ftpuser/guest/

You can also set the quota and maximum space:
1000 files, 100MB quota

pure-pw useradd guest -u ftpuser -d /home/ftpuser/guest/ -n 1000 -N 100 

8.) Set the password in case you forget the enter the password:

pure-pw passwd guest

9.) Update the database:

pure-pw mkdb

That’s it!

–Derrick

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Recently, I found that my dmesg log are filled of junk. Or I should say it contains lots of errors and complains that I already fix. However, I don’t want to reboot the machine to get rid of these error messages. How can I do it? The solution is very simple.

For FreeBSD and other BSD members, run the following:

sudo sysctl kern.msgbuf_clear=1

For Fedora / Ubuntu Linux, run the following instead:

sudo dmesg -c

Easy?

–Derrick

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Recently, I decide to upgrade all of the Fedora Linux servers. As of today, the latest version is Fedora 15. As for my servers, they are in between Fedora 11 and 14. In the other words, I will need to upgrade some machine from 11 all the way to 15.

There are several ways to upgrade the Fedora system. You can either do it through the GUI (With physical access to the machine), GUI (Though VNC), or command line. I prefer the last option because I have limited number of monitors and input devices.

I haven’t tried upgrading Fedora through command line before. The experience is very different comparing to FreeBSD. So I am going to list out what I have done step by step:

1. Backup your data. Although I haven’t experienced any data loss during the upgrade. It is always a good idea to have a backup first.

2. Make sure that your system is up to date with your current version:

sudo yum update

3. Install preupgrade:

sudo yum install preupgrade -y

4. Run the preupgrade:

sudo preupgrade-cli "Fedora 15 (Lovelock)"

It will download the packages from the server. Depending on your system settings, my system downloaded around 1500 packages, which took about 10 to 20 minutes. After that, it will prompt to reboot the machine.

5. This step is optional. Connect your monitor, keyboard and mouse to the machine.

6. Reboot your server

sudo reboot

7. Now the system will boot into the upgrade interface and perform the upgrade. Notice that this step can easily take 2 to 3 hours (My machine: Q6700 Quad Core, Ram: 8GB). During the upgrade, you cannot remotely access the computer. If you try to connect a monitor / keyboard / mouse, it may give no response. Just be patient and wait. It is not a good idea to reboot your machine at this stage.

8. After waiting for nearly 2.5 hour (2 hours to unpack and install the package, half hour to clean up the package), the machine finally reboots.

9. You should be able to remotely access this machine from SSH. Run the following command to determine your Fedora version:

cat /etc/redhat-release && uname -a

10. Run the following commands to clean up the system:

sudo yum update
sudo package-cleanup --orphans
sudo updatedb
sudo yum repolist 
sudo yum distro-sync 

10. Enjoy your new system.

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Recently, I decided to turn my HP m7557c computer (motherboard: A8M2N-LA / NodusM-GL8E) to an Unix server. The nightmare began. After trying nearly 10 different operating systems and distributions, I found that only very few of them worked with A8M2N-LA / NodusM-GL8E. I think it is worth to share my experience with this beast – an experiment result that took more than 100 hours.

I have not failed. I've just found 10,000 ways that won't work.
-- Thomas A. Edison
The following operating system are listed in alphabetically:

Fedora 13
Status: No
Comment: Installation went well, but the system was very unstable due to kernel panic. This mother board may not compatible with the newer Linux kernel.

FreeBSD 7.3
Status: No
Comment: Does not support USB keyword, i.e., can’t start the installation.

FreeBSD 8.1
Status: Yes
Comment: Stable, however the harddrives are very unstable. Sometimes the system complains about the harddrive. See the full story here.

FreeBSD 8.2
Status: Yes
Comment: Very stable. No problem found so far.

OS X 10.4
Status: No
Comment: Installation failed.

OS X 10.5.8
Status: No
Comment: Installation completed, but very unstable. The system reboots itself.

OS X 10.6
Status: No
Comment: Installation failed

Ubuntu 9.10
Status: Yes, stable.

Ubuntu 10.04
Status: No
Comment: If install directly from the disk, the system will not boot. The only possible way is to upgrade from an earlier version. See Ubuntu 10.04 – Can’t boot / Can’t install for details.

Ubuntu 10.10
Status: No
Comment: Cannot even load the installation disk.

Hope my experience is helpful to you.

–Derrick

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Historically, Ubuntu focuses on the user experience such as beautiful graphical user interface, while Fedora focuses on performance. In the other words, the kernel in Fedora distribution is more up-to-dated.

I just upgraded by Ubuntu 10.04 to 10.10 (released on October 10, 2010), I found that the Linux Kernel in Ubuntu is more advanced than Fedora. I am surprised!

#cat /etc/lsb-release && uname -a

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.10
DISTRIB_CODENAME=maverick
DISTRIB_DESCRIPTION="Ubuntu 10.10"
Linux 2.6.35-22-generic #33-Ubuntu SMP Sun Sep 19 20:34:50 UTC 2010 i686 GNU/Linux

and for Fedora 13:

#cat /etc/redhat-release && uname -a
Fedora release 13 (Goddard)
Fedora release 13 (Goddard)
Linux 2.6.34.7-56.fc13.x86_64 #1 SMP Wed Sep 15 03:36:55 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux

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I was having trouble to update my Fedora Linux system by running sudo yum update.

sudo yum update
Loaded plugins: presto, refresh-packagekit
Error: Cannot retrieve repository metadata (repomd.xml) for repository: fedora.
Please verify its path and try again

sometimes I see different sets of error:

http://download.fedoraproject.org/pu...ta/repomd.xml: [Errno 14] PYCURL ERROR 6 - ""

or

http://download.fedoraproject.org/pu...ta/repomd.xml: [Errno 14] PYCURL ERROR 7 - ""

After searching these error messages on Google, I found tons of the workaround methods. Unfortunately, none of them works! Finally, I came up a way to fix this problem.

The reason why you see this error message because your system could not connect to the main Fedora server(At the time of writing this blog, fedoraproject.org has been downed for at least 4 days.), so that your computer is not redirected to any Fedora mirror servers. The easiest way to fix this problem is by specifying a mirror server in your yum repository configuration file.

First, let’s find a mirror that is closed to your location:

Fedora Mirror (Fedoraproject.org)

or

Google Cache

If you have any trouble to access the information, here is a copy of the list:

North America

ftp://limestone.uoregon.edu/fedora/extras
http://limestone.uoregon.edu/fedora/extras
ftp://fedora.bu.edu/extras
http://mirrors.kernel.org/fedora/extras
ftp://mirrors.kernel.org/fedora/extras
rsync://mirrors.kernel.org/fedora/extras
ftp://ftp.muug.mb.ca/pub/fedora/linux/extras/
http://www.muug.mb.ca/pub/fedora/linux/extras/
rsync://rsync.muug.mb.ca/fedora-linux-extras/
http://mirror.hiwaay.net/redhat/fedora/linux/extras/
ftp://mirror.hiwaay.net/redhat/fedora/linux/extras/
rsync://mirror.hiwaay.net/fedora-linux-extras/
ftp://mirror.phy.olemiss.edu/fedora/extras/
http://mirror.phy.olemiss.edu/mirror/fedora/extras/
http://fedora.mirrors.tds.net/pub/fedora-core-extras
ftp://fedora.mirrors.tds.net/pub/fedora-core-extras
rsync://fedora.mirrors.tds.net/fedora-core-extras
http://mirror.cpsc.ucalgary.ca/mirror/fedora/linux/extras/
ftp://mirror.cpsc.ucalgary.ca/mirror/fedora/linux/extras/
rsync://mirror.cpsc.ucalgary.ca/fedora-linux-extras/
http://www.gtlib.gatech.edu/pub/fedora.redhat/linux/extras/
ftp://ftp.gtlib.gatech.edu/pub/fedora.redhat/linux/extras/
rsync://rsync.gtlib.gatech.edu/fedora-linux-extras/

Europe

http://sunsite.mff.cuni.cz/pub/fedora-extras/
ftp://sunsite.mff.cuni.cz/pub/fedora-extras/
rsync://sunsite.mff.cuni.cz/fedora/extras/
ftp://alviss.et.tudelft.nl/pub/fedora
http://ftp.lug.ro/fedora/linux/extras/
ftp://ftp.lug.ro/fedora/linux/extras/
http://ftp.uni-bayreuth.de/linux/fedora/linux/extras
ftp://ftp.uni-bayreuth.de/pub/linux/fedora/linux/extras
rsync://rsync.uni-bayreuth.de/fedora-linux-extras
http://ftp1.skynet.cz/pub/linux/fedora/extras/
ftp://ftp1.skynet.cz/pub/linux/fedora/extras/
ftp://ftp.tu-chemnitz.de/pub/linux/fedora-core-extras/
http://wftp.tu-chemnitz.de/pub/linux/fedora-core-extras/
ftp://ftp.chl.chalmers.se/pub/fedora/linux/extras/
ftp://ftp.udl.es/pub/fedora/linux/extras/
http://ftp.udl.es/pub/fedora/linux/extras/
rsync://ftp.udl.es/pub/fedora/linux/extras/
ftp://gd.tuwien.ac.at/opsys/linux/fedora/extras/
http://gd.tuwien.ac.at/opsys/linux/fedora/extras/
rsync://gd.tuwien.ac.at/opsys/linux/fedora/extras/
http://fr.rpmfind.net/linux/fedora/extras/
ftp://fr.rpmfind.net/linux/fedora/extras/
rsync://fr.rpmfind.net/linux/fedora/extras/
http://mirror.etf.bg.ac.yu/fedora/linux/extras
ftp://mirror.etf.bg.ac.yu/fedora/linux/extras
rsync://mirror.etf.bg.ac.yu/fedora/linux/extras

http://mirror2.etf.bg.ac.yu/fedora/linux/extras
ftp://mirror2.etf.bg.ac.yu/fedora/linux/extras
rsync://mirror2.etf.bg.ac.yu/fedora/linux/extras
ftp://klid.dk/fedora/linux/extras/
http://klid.dk/homeftp/fedora/linux/extras/

Russia

http://ftp.rhd.ru/pub/fedora/linux/extras/
ftp://ftp.rhd.ru/pub/fedora/linux/extras/
ftp://ftp.chg.ru/pub/Linux/fedora/linux/extras/
http://ftp.chg.ru/pub/Linux/fedora/linux/extras/
rsync://ftp.chg.ru/fedora/linux/extras/

Taiwan, Asia

http://ftp.isu.edu.tw/pub/Linux/Fedora/linux/extras/
ftp://ftp.isu.edu.tw/pub/Linux/Fedora/linux/extras/

Australia

http://planetmirror.com/pub/fedora/linux/extras/
ftp://ftp.planetmirror.com/pub/fedora/linux/extras/
rsync://rsync.planetmirror.com/fedora/linux/extras/
http://mirror.pacific.net.au/linux/fedora/linux/extras/
ftp://mirror.pacific.net.au/linux/fedora/linux/extras/

In my example, I will use the following parameters:
Mirror: http://fedora.mirrors.tds.net/
Version($releasever): 12
Architecture($basearch): x86_64

If you are not sure how to determine the version and the architecture, you can type:

cat /etc/redhat-release && uname -a

It should say something like:

Fedora release 12 (Constantine)
Linux 2.6.31.6-145.fc12.x86_64 #1 SMP Sat Nov 21 15:57:45 EST 2009 x86_64 x86_64 x86_64 GNU/Linux

Next, run the following:

sudo nano /etc/yum.repos.d/fedora.repo

and edit the following from:

[fedora]
...
baseurl=http://download.fedoraproject.org/pub/fedora/linux/releases/$releasever/Everything/$basearch/os/

[fedora-source]
baseurl=http://download.fedoraproject.org/pub/fedora/linux/releases/$releasever/Everything/source/SRPMS/

to:

[fedora]
...
#baseurl=http://download.fedoraproject.org/pub/fedora/linux/releases/$releasever/Everything/$basearch/os/
baseurl=http://fedora.mirrors.tds.net/pub/fedora/releases/12/Everything/x86_64/os/

[fedora-source]
...
#baseurl=http://download.fedoraproject.org/pub/fedora/linux/releases/$releasever/Everything/source/SRPMS/
baseurl=http://fedora.mirrors.tds.net/pub/fedora/releases/12/Everything/source/SRPMS/

Now, let’s do something similar to another file:

sudo nano /etc/yum.repos.d/fedora-updates.repo
[updates]
...
#baseurl=http://download.fedoraproject.org/pub/fedora/linux/updates/$releasever/$basearch/
baseurl=http://fedora.mirrors.tds.net/pub/fedora/updates/12/x86_64/

[updates-source]
...
#baseurl=http://download.fedoraproject.org/pub/fedora/linux/updates/$releasever/SRPMS/
baseurl=http://fedora.mirrors.tds.net/pub/fedora/updates/12/SRPMS/

Now, try to run the update again by:

sudo yum clean all
sudo yum update

It should work now. Enjoy your update!

Thoughts:

The reason why this problem happens because the Fedora server is down for at least 4 days(From 12/31 to 1/4, 2010, for four days.), and the problem is not fixed! Yes I know it is in the holiday, but it is not an excuse.

One reason why my company prefers using Fedora Linux is that it has a long history and it is backed by Red Hat. Now the quality of their service seems going down. (Their servers have gone down multiple times in December, and each down time lasted longer than a day.) I think it is probably about time for us to move to a different Linux distribution, such as Ubuntu.

Fedoraproject.org has downed.

FYI, I personally use FreeBSD for all of my server applications.

–Derrick

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I was installing XAMPP on Fedora 11 64-bit today, and I saw this famous message:

sudo /opt/lampp/lampp startapache
XAMPP is currently only availably as 32 bit application. Please use a 32 bit compatibility library for your system.

The message is very clear that XAMPP doesn’t like 32-bit system. So, we will need to cheat XAMPP that the system is 32-bit. First, we will need to install some libraries:

sudo yum -y install glibc.i686 libgcc.i686 libstdc++.i686

and now, we need to skip the 32-bit annoying check. Use Nano or your favorite editor to open this file: /opt/lampp/lampp

sudo nano /opt/lampp/lampp

Replace the following from:

# XAMPP is currently 32 bit only
case `uname -m` in
       *_64)
       if /opt/lampp/bin/php -v > /dev/null 2>&1
       then
               :
       else
               $de && echo "XAMPP gibt es zur Zeit nur als 32-Bit Applikation. Bitte verwende eine 32-Bit Kompatibilitaetsbibliothek fuer Dein System."
               $de || echo "XAMPP is currently only availably as 32 bit application. Please use a 32 bit compatibility library for your system."
               exit
       fi
       ;;
esac

To:

# XAMPP is currently 32 bit only
#case `uname -m` in
#       *_64)
#       if /opt/lampp/bin/php -v > /dev/null 2>&1
#       then
#               :
#       else
#               $de && echo "XAMPP gibt es zur Zeit nur als 32-Bit Applikation. Bitte verwende eine 32-Bit Kompatibilitaetsbibliothek fuer Dein System."
#               $de || echo "XAMPP is currently only availably as 32 bit application. Please use a 32 bit compatibility library for your system."
#               exit
#       fi
#       ;;
#esac

Now run the following the start XAMPP:

sudo /opt/lampp/lampp startapache

Wow! Everything is working great!

–Derrick

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Fedora Linux 12 is out today.

Here are the links to download Fedora 12:

  1. Download Fedora 12 64-Bit
  2. Download Fedora 12 32-Bit
  3. Download Fedora 12 PowerPC
  4. All versions

Suggestions:
I found that the downloading speed varies depends on which mirror you get. I suggest to test the download speed first, and re-try it (using a different mirror) if the speed is too slow.

For example, run the following command in terminal:

wget http://download.fedoraproject.org/pub/fedora/linux/releases/12/Fedora/x86_64/iso/Fedora-12-x86_64-DVD.iso

Which will show you the speed. Simply terminate the command and re-try it if the speed is too low.

Have fun with Fedora 12.

–Derrick

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I was having problem today to send out an email from my Fedora 11 Linux box. By default, the mail server software, Sendmail, comes with the standard installation and no configuration is required. I didn’t understand why the Sendmail didn’t work.

After a very detail investigation, I finally found out why. Here are the steps I went through to solve the problem.

1. Make sure the Sendmail is running.

netstats -na | grep LISTEN

You should see something is running on port 25.

2. Make sure the stupid SELinux Firewall is disabled.

3. Make sure the Linux Firewall allows port 25.

4. Try to connect to the port 25.

telnet localhost 25

If you have trouble to connect to the port, that means something is not work.

5. Make sure you are not blocking port 25 at the system level:
In /etc/hosts.allow

sendmail: localhost: allow

That should work!

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