Use Magic SysRq combination key to recover from a frozen system in Linux | Ubuntu
In our previous post we talked about the magic sysRq key ” RSEIUS” a key combination to be used for emergencies when the system absolutely locks up and freeze, in other word when the systems has already died a horrible death. Today i will show another magic SysRq keys combination to be used to recover from freezes in linux (Ubuntu, Fedora, CentOS..). Note that these keys wont work if your system is in kernel panic.
” The magic SysRq is a key combination understood by the Linux kernel, which allows the user to perform various low level commands regardless of the system’s state. It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem. The key combination consists of Alt, SysRq and another key, which controls the command issued “
1- Activate The magic SysRq key in Ubuntu/Debian/CentOS/RHEL/Fedora
- If you are using Ubuntu,Debian you can not use The magic SysRq key because it is desactivated by default.
If you want to activate it, you have to edit the file /etc/sysctl.conf :
and then add this line :
kernel.sysrq = 1
save and close
- If you are using Fedora /CentOS/ Redhat, edit the file /etc/sysctl.config and change the value of kernel.sysrq to 1
# Controls the System Request debugging functionality of the kernel
# kernel.sysrq = 1
2- List of SysRq magic key combination to recover from a Frozen system:
First, Some keyboards may not provide a separate SysRq key. In this case, a separate “Print” key should be present. Under graphical environments (such as Gnome or KDE) ‘Alt’+'PrintScrn/SysRq’+key combination generally only leads to a screenshot to be dumped. To avoid this Print Screen feature the magic SysRq combination should be additionally prefixed by Ctrl, becoming ‘Ctrl’+'Alt’+'SysRq’+key.
|++||Send the SIGTERM signal to all processes asking them to exit except init|
|++||Send the KILL signal to all running processes except init.|
|++||Kill all processes on the current virtual console (Can be used to kill X and svgalib programs)|
|++>||Turn off keyboard raw mode. This can be useful when your X session hangs. After issueing this command you may be able to use|
|++||Send the KILL signal to all processes, including init. The system will not be functional.|
|++ >||Reboot immediately without syncing or unmounting your disks. Your will likely end up with filesystem errors.|
Sync all mounted filesystems. This is helpfull because it can prevent data loss.
Shut the system off (if configured and supported).
Display help. Also, any other unsupported combination will display the same help.
To perform a safe reboot of a Linux computer, use RSEIUB magic SysRq Magic combination key:
Hold Alt+PrtSc then type R+S+E+I+U+B , you need to press each key for 2-3 seconds.
In practice, each command may require a few seconds to complete, especially if feedback is unavailable from the screen due to a freeze or display corruption. For example, sending SIGKILL to processes which have not yet finished terminating can cause data loss.
Like us on Facebook
We need your assistance to stay live
This week Top Posts
- Top Things To Do After Installing Ubuntu 13.10 'Saucy Salamander' : Ubuntu 13.10 Saucy Salamander will be released on coming October 17th with many new salient featur...0 comments |
- Fedora 21 Scheduled For Release In October : For Fedora users, just keep calm and use Fedora 20 for now. Fedora Developers has announced that F...1 comment |
- How To Upgrade From Ubuntu 13.04 Raring To Ubuntu 13.10 Saucy Salamander : Ubuntu 13.10 Saucy will be released on October 17th. Hope it will come with lot of improvements and ...0 comments |
- Install LAMP Server (Apache, MySQL or MariaDB, PHP) On Ubuntu 13.10 : Updated January 12, 2014 LAMP is a combination of operating system and open-source software stack. ...0 comments |
- Install lamp with 1 command in Ubuntu 12.10, 13.04 Raring Ringtail & LinuxMint13 : Updated: 10/09/2012 :LAMP (Linux, Apache, MySQL and PHP) is an open source Web development platform ...0 comments |
- Download Elementary OS 'Luna' Official Wallpapers : Hi Guys, Am a great lover of Elementary OS, so I like to move almost everywhere with some its beaut...0 comments |
- Fedora 21 Scheduled For Release In October
- Install Uget Download Manager In Ubuntu, Fedora, Debian
- Download Elementary OS ‘Luna’ Official Wallpapers
- Install Power Commands 0.1.5 On Ubuntu 14.04/13.10/12.10/12.04
- 5 Android Apps that’s Going to Make Running Your Business Less Stressful
- Puppet agent Install Using Script
- Install Corosync and Pacemaker On CentOS 6.5
- Install Fail2Ban On Ubuntu Server 13.04/13.10
- How To Install Google Chrome in Fedora 20, 19, 18
- How to surf using Tor Browser Bundle
This work by unixmen.com is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
Copyright © 2008-2013 Unixmen.com .