June 2015 – SudoAll.com

Kernel: e1000e 0000:02:00.0: eth0: Error reading PHY register

Posted on June 28, 2015 by admin

In recent CentOS version 6.3 is an unresolved bug, which causes the network card to freeze the server.

Following message appears in /var/log/messages

kernel

To work around the problem you will need to turn off Active-State Power Management (ASPM)
(Feature that saves power in the Peripheral Component Interconnect Express (PCI Express or PCIe) subsystem by setting a lower power state for PCIe links when the devices to which they connect are not in use)

For GRUB bootloader edit the following file: /boot/grub/grub.conf and append pcie_aspm=off to the end of kernel boot line.

For example:

kernel /vmlinuz-2.6.32-279.el6.x86_64 ro root=UUID=81e9e0a2-0a51-4d75-955d-909aaf848192 rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=us LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_NO_DM rd_MD_UUID=c6855f45:016a63bb:2d79bfb2:07371ed8 rd_NO_LVM rd_MD_UUID=5d5a434e:6c20cfcd:51340c3f:29c29151 pcie_aspm=off

To verify the change, reboot the server and run the following command:

dmesg | grep PCIe
PCIe ASPM is disabled

If your output is different, the change in grub.conf did not take an effect.

UDP send and listen for passing messages and test connectivity

Posted on June 8, 2015June 8, 2015 by admin

Setting up a listener in UDP :

Install socat

Jist here (Centos 6.6 : http://jist.sudoall.com/socat/setup

install

curl “http://jist.sudoall.com/socat/setup” | bash –

socat -u udp-recv:8888 –

To send the datagram :

nc -u 127.0.0.1 8888

njoy 😉

Magic SysRq key

Posted on June 2, 2015June 2, 2015 by admin

The “magic SysRq key” provides a way to send commands directly to the kernel through the /proc filesystem. It is enabled via a kernel compile time option, CONFIG_MAGIC_SYSRQ, which seems to be standard on most distributions. First you must activate the magic SysRq option:

echo 1 > /proc/sys/kernel/sysrq

When you are ready to reboot the machine simply run the following:

echo b > /proc/sysrq-trigger

This does not attempt to unmount or sync filesystems, so it should only be used when absolutely necessary, but if your drive is already failing then that may not be a concern.

In addition to rebooting the system the sysrq trick can be used to dump memory information to the console, sync all filesystems, remount all filesystems in read-only mode, send SIGTERM or SIGKILL to all processes except init, or power off the machine entirely, among other things.

nJoy 😉