Skip to main content

You are here

Kernel

Emergency reboot in Linux via SysRq

When your Linux system has completely shit itself, and an emergency reboot needs to be made. Linux Magic System Request Keys to the rescue.

[[email protected] ~]# echo "1" > /proc/sys/kernel/sysrq
[[email protected] ~]# echo "b" > /proc/sysrq-trigger

Resources: https://www.kernel.org/doc/Documentation/sysrq.txt

Linux: 

ZFS on Linux: Installation

Attending the ZFS Administration talk on SCALE 11x a couple of weeks ago made me interested in trying ZFS on Linux. Given that the speaker said that he uses ZFS on Linux on his production machines, made me think that ZFS on Linux may be finally ready for everyday use. So I'm currently looking into using the ZFS snapshots feature for my personal local file backups.

For my Linux ZFS backup server, I'm using the latest CentOS 6. Below are the steps I took to get ZFS on Linux working.

yum install automake make gcc kernel-devel kernel-headers zlib zlib-devel libuuid libuuid-devel

Since the ZFS modules get build using dkms, the latest dkms package will be needed. This can be downloaded from from Dell's website at http://linux.dell.com/dkms/

wget http://linux.dell.com/dkms/permalink/dkms-2.2.0.3-1.noarch.rpm
rpm -ivh dkms-2.2.0.3-1.noarch.rpm

Now, the spl-modules-dkms-X rpms need to be installed.

wget http://archive.zfsonlinux.org/downloads/zfsonlinux/spl/spl-0.6.0-rc14.sr...
wget http://archive.zfsonlinux.org/downloads/zfsonlinux/spl/spl-modules-0.6.0...
wget http://archive.zfsonlinux.org/downloads/zfsonlinux/spl/spl-modules-dkms-...
rpm -ivh spl*.rpm

After the spl-modules-dkms-X rpms have been installed, the ZFS rpm packages can now be finally installed.

wget http://archive.zfsonlinux.org/downloads/zfsonlinux/zfs/zfs-0.6.0-rc14.sr...
wget http://archive.zfsonlinux.org/downloads/zfsonlinux/zfs/zfs-modules-0.6.0...
wget http://archive.zfsonlinux.org/downloads/zfsonlinux/zfs/zfs-modules-dkms-...
rpm -ivh zfs*.rpm

One thing that confused me was that after all rpm's were installed, the zfs or zfspool binaries were no where on my system, which according to the documentation the zfs-* rpm process would have build the kernel modules and installed them on my running kernel, however this didn't look to be the case. http://zfsonlinux.org/zfs-building-srpm.html
Instead I had to do the following:

cd /usr/src/zfs-0.6.0
make
make install

After the install completed both zfs and zfspool utilities were available and ready to use.

Linux: 

Awesome Applications: 

Logging iptables rules

When debugging certain custom firewall rules, it can sometimes be extremely useful log the rule's activity.
For example, the following rule logs all input firewall activity. The logs will be available via dmesg or syslog.

iptables -A INPUT -j LOG --log-prefix " iptables INPUT "

Awesome Applications: 

Compiling the Linux Kernel

You can't call yourself a serious GNU/Linux user if you have never successfully compiled the Linux kernel at least once in your life.

The following were the steps I made to compile the Linux kernel over 4 years ago (I just happened to find my reference text file that I saved, buried within my home directory).

1. Download kernel source code from http://www.kernel.org .
2. Extract kernel source.
3. Update EXTRAVERSION variable on Makefile
4.(only do steps 4 if a previous kernel compilation was made within this source tree) make mrproper (goes through the source tree and cleans out temp files)

make mrproper
make clean

6. make menuconfig (actual configuration of the kernel compilation. creates .config file)

make menuconfig

7. make (performs the actual compilation. creates bzimage file. makes the modules)

make

8. make modules_install (install modules into /lib/modules)

make modules_install

9. make install (will automatically copy the kernel and initrd file to /boot and modify the boot loader config file)

make install

(reference one liner):

make clean dep bzImage modules install modules_install

Linux: 

Premium Drupal Themes by Adaptivethemes