The Linux kernel is the operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software.

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KVM - task foo:1234 blocked for more than 120 seconds - howto change task scheduler

I recently installed a new Debian Wheezy server with KVM (the "KVM Host") then installed a Debian VM on the KVM (the "VM"), and got very bad performance on the VM. Looking through dmesg on the VM, I ...
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1answer
400 views

linux initcwnd and initrwnd via /etc/sysctl.conf

Folks, As we know, the 3.x kernels have higher TCP default connection values, such as initcwnd and initrwnd. For 2.x friends, is there a way to set these in /etc/sysctl.conf instead of the ip route ...
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1answer
160 views

What is the purpose of /proc/config.gz

Please what is the purpose of the /proc/config.gz file in my Linux server filesystem? Is it some backup file, or it is an updated file by the Linux system? Can I change it?
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3answers
379 views

High CPU usage in random IP/Port UDP DDoS

I have been getting these UDP floods with random IPs and ports. randomip:randomport -> myip:randomport 0 byte payload For some reason it is using a lot of CPU. Here is the results of perf top -e ...
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2answers
417 views

Can't resolve issue: iptables: No chain/target/match by that name

So I am trying to setup shorewall firewall on my linux vps. The vps is running ubuntu 12.10. When I type $ shorewall check I get this error. iptables: No chain/target/match by that name. ERROR: ...
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2answers
515 views

/var/log/messages showing lots of CE Err=0x2000 even on unused banks (slots)

I recently had to upgrade an old server (HP ML350G5) with used FBDIMM DDR2 RAM (could not get new ones where I live). After rebooting /var/log/messages has been plagued with CE Err=0x2000 errors but ...
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1answer
72 views

Fixed TCP payload Size [closed]

I have an aplication that need to have a fixed (516 byes) payload size in the TCP packet. The application itself can't be modified to adjust it settings, therefore i need to tune the TCP Buffer Size ...
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4answers
708 views

MySQL 5.5 degraded performance in linux kernel 3.2 compared to 2.6

Our database servers (mainly based on the Debian stable packages (=currently Wheezy) seem to have about 4 times more load for the same workload in kernel 3.2.0-4-amd64 then in it's previous ...
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0answers
137 views

Capturing on loopback device on Ubuntu LTS: 15 Mbit of traffic and “x dropped packets”

I am trying to capture about 15 Mbit of traffic on the loopback device on Ubuntu LTS using tcpdump, and I am seeing dropped packets. The CPU is a freaking i7, and i have yet to see CPU usage go above ...
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1answer
47 views

forcing linux kernel 3 to recognize cdrom as hdX

I have a problem with older version of anaconda linux installer. I have upgraded kernel in my distro, however, when this anaconda boot with this 3.4.52 kernel, can NOT find cdrom. As far as I ...
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1answer
193 views

Linux (non-transparent) per-process hugepage accounting

I've recently converted some java apps to run with linux manually-configured hugepages, as desribed here. I point out "manually-configured" because they are not transparent hugepages, which gave us ...
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0answers
347 views

Kernel panic - not syncing: VFS: Unable to mount root

I uploaded a centos 6.2 VMDK to s3 and then converted it to volume using ec2 import volume. Then i took the snapshot of the volume and deleted it.Now I am trying to create a instance from the snapshot ...
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1answer
418 views

What is required to activate cgroups in Linux

I have a Debian squeeze kernel (linux-image-2.6.32-5-openvz-amd64) which according to the Doku should support cgroups. When I look into the kernel configuration, it does (or is some other kernel ...
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1answer
405 views

please explain my fio results - is O_SYNC|O_DIRECT misbehaving on linux?

I'm going mad over figuring out what the problem could be with one of our storage boxes. With a simple fio script I'm testing random writes using bs=1M and direct=1. The SSD is a Samsung 840pro ...
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1answer
56 views

Debian squeeze kernel update under Security Updates

Can someone explain what squeeze1 and squeeze3 designate at the end of a kernel name? For instance 2.6.32-48squeeze3 is showing up under Security Updates in Aptitude.
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0answers
115 views

linux kernel configuration to filter multicast traffic based on interface

I have two virtual interfaces (eth0.2, eth0.3) in my PC. I am sending multicast data from eth0.2 to eth0.2. Multicast data is received in eth0.2 but also received in eth0.3, the other virtual ...
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1answer
258 views

How to enable CONFIG_PREEMPT option in Linux kernel? [closed]

I am a new bee in Linux kernel programming, trying to work with an old kernel Linux 2.6.32 on x86_64. I want to enable the CONFIG_PREEMPT option in it but can not find information about how can I do ...
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0answers
49 views

Sun Fire V40z, big gap between memory reported by dmidecode and what the Linux kernel sees

I'm looking after a V40z (a loaner), running RHEL 4.8 (no, I can't update it, it's a loaner) that according to dmidecode has 8 DIMMs of 2048M each, which makes for 16GB RAM as far as I'm concerned. ...
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1answer
136 views

Linux not freeing the file buffer when we execute rm or > (redirection) operator

I have one router which has embedded-linux with kernel version 2.4.22 running on it. I know its very old version but i have to deal with it. Please take a look at the free command output when i run it ...
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1answer
671 views

RHEL 6.0 upgrading kernel from 2.6.32-71.el6.x86_64 to 2.6.32-358.2.1.el6.x86_64

[root@localhost ~]# rpm -ivh kernel-2.6.32-358.2.1.el6.x86_64.rpm error: Failed dependencies: bfa-firmware < 3.0.3.1 conflicts with kernel-2.6.32-358.2.1.el6.x86_64 [root@localhost ~]# rpm ...
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2answers
2k views

Kernel 3.8, Apache2 with WSGI : INFO: task apache2 blocked for more than 120 seconds

We have upgraded our Kernel from 2.6.32 to 3.8.7 on a Debian system. We have a sharing with NFS to get the data for Apache2. And Nginx serves only static files as a proxy. Since we have installed the ...
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5answers
2k views

Intentionally cause an I/O error in Linux?

Is there anyway, with Linux, to purposely cause a block device to report an I/O error, or possibly simulate one for testing purposes?
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1answer
99 views

How to check/set linux’s “security level”? [closed]

I got recommended here to check the kernel's security level—how can I print it out on a linux machine? (SLES?) If it’s set too low, how can I increase it? If I set it too high, can I ever set it ...
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1answer
549 views

Linux KVM: Troubleshooting dropped packets on a Windows Guest

virsh 0.9.10 Enterprise Linux 6.3 I have a Windows 7 guest running on the KVM host and am frequently seeing 25% loss when pinging other boxes on the same subnet. The first ping request times out, and ...
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1answer
240 views

understanding ip route show command on linux [closed]

I have a Windows 7 PC as host.The network details of my Windows PC are as follows. IP ADDRESS - 192.168.1.70 DEFAULT GATEWAY - 192.168.1.254 I have installed Virtual Box ...
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1answer
186 views

Issues with Xen Kernel and Debian

My Xen installation has gone weird on me and I am trying to get back to normal. I overflowed the base partition and in my haste to delete unused files I think I deleted something important, so now ...
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2answers
528 views

Why does my server boot the old debian kernel?

I got a vServer with Debian installed (important because I have no idea of how Debian was installed and/or built). Output of ~# uname -r: 2.6.26-2-xen-amd64. After execution of (first some other ...
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1answer
939 views

Cannot find network subsystem in cgroup on Ubuntu 12.04 LTS

I'm trying to use cgroups to limit a process's network bandwidth, as described in this answer. However, I am unable to find the "files" they refer to. I am using Ubuntu 12.04 LTS with cgroup-bin ...
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0answers
402 views

netmap issue with wheezy linux kernel 3.2.0.4 and Intel Corporation 82599EB 10-Gigabit card

I have compiled the netmap drivers on debian wheezy with kernel 3.2.0.4 and ixgbe patched module from netmap drivers code. When I insert the modules after removing default ixgbe module I get the ...
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1answer
581 views

Centos 6.3 DRBD / OpenVZ kernel/userland issue

When I start my Centos 6.3 server's drbd service I get the following error: Starting DRBD resources: DRBD module version: 8.3.13 userland version: 8.4.2 preferably kernel and userland versions ...
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1answer
488 views

Debian Wheezy No longer booting. Freezes after setting kernel variables

My Debian (Wheezy) server has been running smoothly for a very long time with no indications of any problems. I had it running 24/7 so it was always on. The other day my power went out and when I ...
2
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2answers
304 views

Linux process swap usage is greater than the overall system swap usage

I have a strange problem that when I run top command it shows that some processes are using around 1.5GB of swap space but then the overall usage of the system swap is way to less to something around ...
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4answers
529 views

Linux high load with ImageMagick convert utility and server freezes (blktrack output attached)

I'm using ImageMagick to convert a JPG to TIF file, and I'm using the limit options for Imagemagick as below: /usr/bin/convert -limit memory 256 -limit map 512 subjectfile.jpg -colorspace Gray -depth ...
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1answer
297 views

CentOS server high load and server freezes

My server seems to get sudden high loads within second and when I run dmesg, following logs appear: INFO: task auditd:2185 blocked for more than 120 seconds. "echo 0 > ...
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2answers
792 views

XEN kernel shows less memory 32g

I have installed Oracle Enterprise Linux 64bit on the server with 64g of RAM. But the system detects just 32b of memory, here are the details: [root@oracle-node2 ~]# uname -a Linux ...
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1answer
183 views

Scientific Linux: soft lockup on quad opteron system

After an impressive uptime of 550 days without trouble our quad opteron system turned into a corrupted system a few days after I mounted an nfs-share from a FreeNAS-box. Ongoing sessions remained ...
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2answers
2k views

Xen Paravirtualized Guest - Invalid Kernel

I have set up xen on ubuntu server 12.04 LTS. I have tried installing a guest to an lvm I created called xen-lvm The virt-install script: sudo virt-install \ --name client2-ubuntu-server \ --ram 512 ...
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1answer
452 views

CentOS 6.3 with kernel-ml(3.7.1-2.el6.elrepo.x86_64) - No Console Output

I installed kernel-ml(3.7.1-2.el6.elrepo.x86_64) from elrepo on CentOS 6.3, and everything is working fine, except that I see nothing on the console and can't interact with it. I can SSH to the ...
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2answers
175 views

using Linux as a bootloader?

I have an embedded device with a SPI connected flash. Basically this means the device boots its bootloader and Linux kernel from a small flash part. As the device boots, but before the root ...
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1answer
269 views

/proc/<pid>/stat children CPU time

I've been running the following command on my linux box: watch -d -n 1 "cat /proc/19866/stat" The pid above is a pid of Nginx's master process - I would expect the following fields to be changing: ...
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2answers
473 views

Server freezes and suddenly load going very high

I'm on CentOS 5.7 and I get server freezes quite a lot and the logs show the following output: Dec 26 18:33:51 server kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this ...
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1answer
1k views

Where are the acpiphp and pci_hotplug kernel modules for KVM hotplug in CentOS/RHEL?

On the this how-to I read the following: I loaded the following modules to get pci hotplug working: acpiphp pci_hotplug You can either add these to your distro's module list to ...
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1answer
69 views

Which Flavour of Linux comes with default kernel 3.4? [closed]

I was using centos but came to know it has restrictions to upgrade kernel version so looking for any other flavour with default 3.4 kernel version please suggest
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4answers
20k views

In CentOS 6.x, how can I upgrade to Kernel 3.4?

I have a server with CentOS 6.2 with kernel version 2.6.32, but I need to increase my application Performance. The Kernel Version 3.4 has x32abi which can improve the performance so i want to upgrade ...
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1answer
890 views

How can I confirm if my CentOS server supports multiple CPUs?

CentOS 5.8 | VMWare I've got a server running a hardened version of CentOS 5.8. I've been using a single CPU on it and am planning to add another (via vmware). When I run uname, I see SMP which ...
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1answer
2k views

CentOS 6.3 task blocked for more than 120 seconds

Recently have been getting Zabbix alerts about our mail system being unavailable, the uptime on the machine is 30+ days. I've been tracing the Zabbix logs and it looks like the communication between ...
0
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1answer
86 views

Size of modules within initrd

I am currently trying to manually replace the kernel within ubuntu-core on an embedded device with a custom kernel. However when I try to update the initrd my initrd becomes much bigger. Here is what ...
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1answer
519 views

How to stop a infinite running process(ztail) started by a ssh session after that session is closed

I have a peculiar problem. My server supports multiple ssh session simultaneously, so that multiple admins can manage it simultaneously. We have a command which calls ztail to show the compressed log ...
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1answer
245 views

Nonstandard kernel on CentOS

CentOS/RH is very widely supported as a server distro, but it mounts a somewhat older kernels. For example now it runs kernel 2.6, while 3.6 is already out. I found several tutorials about upgrading ...
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1answer
225 views

what is occupying linux low memory

How can I find what is occupying my low memory on 32 bit Linux OS? cat /proc/meminfo |grep Low LowTotal: 812908 kB LowFree: 43340 kB Regards,