Ksplice: Upgrade / Patch Your Linux Kernel Without Reboots

Posted on in Categories Linux last updated April 9, 2010

Generally, all Linux distributions needs a scheduled reboot once to stay up to date with important kernel security updates. RHN (or other distro vendors) provides Linux kernel security updates. You can apply kernel updates using yum command or apt-get command line options. After each upgrade you need to reboot the server. Ksplice service allows you to skip reboot step and apply hotfixes to kernel without rebooting the server. In this post, I will cover a quick installation of Ksplice for RHEL 5.x and try to find out if service is worth every penny.

Linux: Display Japanese or Chinese Or Any Other Multilingual Text On The Console / Shell Prompt

Posted on in Categories CentOS, Debian Linux, GNU/Open source, Howto, kernel, Linux, Linux desktop, Linux distribution, News, RedHat/Fedora Linux, Sys admin last updated July 16, 2008

Explains how to display multilingual text such as hindi, chinese, japanese, korean etc text on the console using framebuffer, and bterm applications under Fedora / RHEL / CentOS / Debian / Ubuntu Linux.

How To: Double Linux disk read performance with readahead parameter

Posted on in Categories CentOS, Debian Linux, File system, Hardware, Howto, Linux, RedHat/Fedora Linux, Storage, Suse Linux, Tuning last updated November 22, 2007

The open source journal has published an interesting hack. It mostly applies to high-end, multiple-disk storage:

Under the right conditions (that is, with certain hardware configurations which I’ll identify later) it is possible to literally double your sequential read performance from disk. If you noticed the terrible performance of the 3Ware 9500S RAID controller and cared enough to investigate. It all has to do with a sneaky little block device parameter known as readahead. Without going into too much gory detail, readahead controls how much in advance the operating system reads when, well, reading, as its name implies. By default, some operating systems (in particular, RHEL5 Server) sets this to 256 (512-byte sectors), or about 128 KB. When dealing with large filesystems spanning many disks, this paltry figure can actually nuke your performance.

=> HowTo: Linux: Double your disk read performance in a single command

How to: Control Amarok Media Player with Bluetooth Enabled Phone

Posted on in Categories Howto, Kde, Linux, Linux desktop last updated September 5, 2007

This is a nice hack and a small how to about controlling Amarok media player:

Ever since I’ve received my new phone, bluetooth has excited me. To be honest, the notion of being able to control my pc from the phone was the exciting aspect. Ever wondered how to do this? Let me elaborate.

How to: Control Amarok Media Player with Bluetooth Enabled Phone
(Image Source: Authors blog)

=> Control Amarok with Bluetooth

Fedora Linux add MP3, Java, DVD Playback and multimedia support

Posted on in Categories Download of the day, Howto, Linux, Linux desktop, Linux distribution, RedHat/Fedora Linux last updated September 3, 2007

Copyright/IP laws prevent shipping multimedia and mp3 software(s) and technologies/plugins with Linux distribution. Fedora is no exception to this rule. All you have to do is add few repos and you are ready to go.

Fellow Linux blogger James has published an excellent shell script hack (Fedora Feather) that adds MP3 and multimedia support to Fedora Linux:

Tired of manually adding support for mp3, dvd and Java to your fresh Fedora installs? This script will automatically do all of that.

=> Download Fedora Feather

Howto Reboot or halt Linux system in emergency

Posted on in Categories CentOS, Debian Linux, Gentoo Linux, Howto, Linux, Linux distribution, Networking, RedHat/Fedora Linux, Security, Suse Linux, Sys admin, Tips, Troubleshooting, Ubuntu Linux last updated August 25, 2005

Linux kernel includes magic system request keys. It was originally developed for kernel hackers. However, you can use this hack to reboot, shutdown or halt computer safely (remember safe reboot/shutdown == flush filesystem buffers and unmount file system and then reboot so that data loss can be avoided).

This is quite useful when Linux based system is not available after boot or after a X server crashed ( svgalib program crashes) or no display on screen. Sysrq key combo forces the kernel to respond it regardless of whatever else it is doing, unless it is completely locked up (dead).

Using further extension to iptables called ipt_sysrq (new iptables target), which allows you to do the same as the magic sysrq key on a keyboard does, but over the network. So if your network server is not responding you can still reboot it. Please note that Magic SysRq support need to be compiled in your kernel. You need to say “yes” to ‘Magic SysRq key (CONFIG_MAGIC_SYSRQ)’ when configuring the kernel. I’m assuming that you have Magic SysRq key’ support is compiled in your kernel.

Enable sysrq keys

By default it is not enabled on many Linux distributions. Add or modify following line (as soon as new Linux system installed) /etc/sysctl.conf:
# vi /etc/sysctl.conf
Append following config directive:
kernel.sysrq=1
Save and close the file. Reload settings:
# sysctl -p

Save and close the file and reboot system to take effect

How do I use the magic SysRq keys in emergency?

You need to use following key combination in order to reboot/halt/sync file system etc:
ALT+SysRq+COMMAND-KEY

The ‘SysRq’ key is also known as the ‘Print Screen’ key. COMMAND-KEY can be any one of the following (all keys need to hit simultaneously) :

  • ‘b’ : Will immediately reboot the system without syncing or unmounting your disks.
  • ‘o’ : Will shutdown your system off (if configured and supported).
  • ‘s’: Will attempt to sync all mounted filesystems.
  • ‘u’ : Will attempt to remount all mounted filesystems read-only.
  • ‘e’ : Send a SIGTERM to all processes, except for init.
  • ‘h’: Show help, indeed this the one you need to remember.

So whey you need to tell your Linux computer to reboot or when your X server is crashed or you don’t see anything going across the screen then just press:

ALT+SysRQ+s : (Press and hold down ALT, then SysRQ (Print Screen) key and press ‘s’) -Will try to syn all mounted system

ALT+SysRQ+r : (Press and hold down ALT, then SysRQ (Print Screen) key and press ‘r’) -Will reboot the system.

If you wish to shutdown the system instead of reboot then press following key combination:
ALT+SysRQ+o

ipt_sysrq is a new iptables target that allows you to do the same as the magic sysrq key on a keyboard does, but over the network. Sometimes a remote server hangs and only responds to icmp echo request (ping). Every administrator of such machine is very unhappy because (s)he must go there and press the reset button. It takes a long time and it’s inconvenient. So use the Network Magic SysRq and you will be able to do more than just pressing a reset button. You can remotely sync disks, remount them read-only, then do a reboot. And everything comfortably and only in a few seconds. Please see Marek Zelem page to enableIP Tables network magic SysRq function.

For more information read official Documentation for sysrq.c version 1.15 stored in /usr/src/linux/Documentation/sysrq.txt and read man page of sysctl, sysctl.conf.