Linux Tips & Tricks

Although there are many shells available for Fedora, RedHat and its clones, such as tcsh, ksh, sh and the like, up until now bash still remains the default shell of choice.  This does not come as a surprise because bash (which stands for Bourne Again Shell) has numerous lightning fast built-in commands that can manipulate and explore system on large and limited scales.

Many times I observed, that Linux sysadmin beginners remember remember well how to move among the commands by pressing up and down arrows. They also remember how to use Tab in the command line for completion. Yet, somehow they forget that a great bash command history will pull out the complete history list of commands that they used.

Naturally, getting to see the whole list of commands might not come handy. It is much better, for example,  to go back to the last 10 commands and type in the terminal history 10. This will do the trick.

There are so many other built-in bash history commands that it will take hefty hundred pages to describe them all. I just want to mention another useful history manipulation command that is called simply fc.  This one is very valuable becaue it allow you to open vi editor and run the command after editing it to your liking. For example, fc 356 will allow you to edit this command in vi and then immediately invoke it for you.

During updates your old Linux kernels pile up.  Then one day when you try to do your next updates, an interesting alert comes up from the server.  Basically, it tells you that your boot partition is full and can not fit any more kernels.  Sounds easy, right? It will be easy for those of you who is pretty crafty with terminal and debugging.  We have seasoned sysadmins in our web analytics company, but, naturally, there are junior guys who are still in constant learning process.

Unfortunately, those of them who are used to web interface, like Webmin, will delete their old kernels but won’t be able to proceed with the installation of a new Linux kernel. Interestingly enough, great Webmin just does not show all installed kernels. Some kind of a bug, I guess.

Well, your solution is to open the terminal and find out how many kernels are there anyways. So you need to type up:
rpm -q kernel | sort

Then you need to find out which kernel is the default one on your machine. So invoke the following command on your terminal:

uname -r

Then while whistling some funny melody, start uninstalling one by one all useless kernels. Here is the command:

rpm -e kernel(and its version)

Don’t forget to reboot.  The alert would not bother you anymore.

Note: Please, be careful with uninstallation. Don’t erase all kernels, leave at least a couple of them in case a new update is gonna cause you problems.  In that case, you will just switch back to the old kernel and wait for another kernel update.

I went up through setting up and configuration of Fedora server. The installation went incredibly smooth. I must admit that Sulphur is lightning fast, although I loaded my server with over 1200 files. I followed almost to the point the advice of another Howto on Forge.org who recommends to stop the following services in order to free system resources and enhance security. The guy tells us to disable the following:

• acpid
• anacron
• apmd
• autofs
• bluetooth
• cups
• firstboot
• gpm
• haldaemon
• messagebus
• mdmonitor
• hidd
• ip6tables
• kudzu
• lvm2-monitor
• netfs
• nfslock
• pcscd
• portmap
• rpcgssd
• rpcidmapd
• sendmail
• smartd
• yum-updates

I agree with most of his choices but would recommend to proceed carefully. I recall that once after I disabled cups services on one of Linux machines(because I did not intend to use the server for printing), the machine kept on generating errors until I just damned it all and enabled it back. For that reason I would not recommend for you to disable messagebus, kudzu and lvm2-monitor. Besides, some of you may be using Midnight Commander, so you will definitely need gpm. And those of you who prefer sendmail as your SMTP and iptables for security would, naturally, keep them too.

There is another suggestion. If you have time and resources don’t move your critically important stuff to the newly set up server. Give it time and let it steam for a while. Check the logs from time to time and see how it runs. This is especially true with experimental platforms like Fedora. You don’t wanna get stressed with unusual kernel panics or unexpected freezing of some services at the time when you don’t expect it.

By making sure that everything is in sync and working well, you will save your time and money and will have a hi-quality server that will run headache-free for the next several years. Among servers park of our web analytics company we still have older versions of Fedora servers running smoothly for over three years without causing us problems. We tested each platform for thirty days each before moving them to do some serious business for us.

Fedora 9 has arrived at last. Naturally, I already downloaded and burned the discs. But before I start setting and testing Fedora as a server and a desktop, I need to do my reading. As an ancient Chinese proverb says: “if you participate in the unknown game, never make a first move”. I already brushed through multiple reviews of beta and pre -release versions. But I need to read a review of somebody with reputation about the final version. This is the requirement of our web analytics company too.

There is already some interesting material in HowtoForge written by a famous volunteer Falco. There is also a new material describing setup of a Fedora 9 desktop as well. Falco’s recommended server configuration is based on the following applications: Apache web server (SSL-capable) with PHP5 and Ruby, Postfix mail server with SMTP-AUTH and TLS, BIND DNS server, Proftpd FTP server, MySQL server, Dovecot POP3/IMAP, Quota, and ISP firewall.

I am not much into Ruby, so I will get by without it. And I prefer Sendmail to Postfix, so I will go along with it. As usual, Falco does not use Iptables firewall but chooses ISPConfig, while I like Iptables and plan to use it.

There were several bugs that Falco discovered during setup, probably for the first time, especially with Network Manager that prevents to connect properly to Internet. I have encountered minor problems with Network Manager too and always disabled it, so it would not interfere with my network choices. He also disables SELinux and I wholeheartedly agree with this choice because SELinux caused me a lot of grief before. There are other more comprehensive ways to make your system secure unless one has some kind of paranoia.

I don’t recommend installing either proftpd or vsftpd unless you plan to provide web hosting services or want multiple users to access your server. You can also decide for yourself whether you want to install Webalizer or you would like to process your logs differently.

You also have a choice to install your server with or without Gnome. If before visual interface for the server created unnecessary overhead, now with all dual core and quad core processors and abundance of memory of modern computers, just indulge yourself a little. Go wild and install the GNOME.

Fedora 9 is almost here! I installed a counter which I will naturally remove as soon as Fedora 9 will be available for download. This new version is called Sulphur and promises new exciting features, like Firefox 3, Bluetooth enhancements, ext4 filesystem support.

Developers also promise to improve USB support - live USB images will persist between booting at last.  There is much more, but I will just wait and see. True, there will be bugs to clean and adjustments to make. But if you go through with customization, it is very rewarding experience. In spite of what people say about Fedora, its instability and all, this Linux version is great for experimentation. I have several Fedora servers that I customized personally, and, surprisingly, they outlived some RedHat and CentOS machines. Besides, Fedora is great for learning Linux and understanding what future holds for Linux.

As for comparison between Fedora and Ubuntu, it is hard for me to say. I have a couple of Ubuntu desktops and they are fine. But I am not much into desktops anyways. Sometimes, there are tasks that require a robust small server and customized Fedora is the way to go.