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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How can I directly read data from a file in Linux without using the filesystem cache?

I have shared storage which is mounted (read-only) on SERVER1, and mounted (read-write) on SERVER2. SERVER2 is writing data to a file. SERVER1 is reading data from that file. The file poling is ...
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24 views

Write cache settings not working

I am using Debian 8.0 x64 with 72 GB of RAM with 4 drives configured as software RAID 0. Linux s1 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1 (2015-05-24) x86_64 GNU/Linux I tried setting dirty ...
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1answer
136 views

Can't get rid of mystery kernel

Just noticed that despite having the kernel updated regularly, the version in use is quite outdated: $ uname -a Linux test 2.6.31-302-rs #7 SMP Thu Oct 29 22:57:03 UTC 2009 x86_64 x86_64 x86_64 ...
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4answers
65 views

When does an upgrade update the Ubuntu kernel?

I'm a little confused by Ubuntu/Linux kernel updates. Coming from a Windows background I sort of expect all updates to be available via the update manager, in the case of Ubuntu apt/aptitude. Yet if ...
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25 views

How to disable fibre channel LUNs entirely while doing an OS install?

SL 6.5 (aka RHEL 6.5) using a Qlogic adapter in a Dell R610. The module that is loaded is qla2xxx but also scsi_transport_fc. I have 2 SAS disks in RAID 1 for the OS and several FC LUNs for data ...
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3answers
114 views

kswapd often uses 100% CPU when swap is in use

Most of the time when my computer starts to need swap, I see a massive spike in CPU usage (kswapd0 is consistently using 99%-100% CPU). According to top, the time is spent in sy (system/kernel) not wa ...
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32 views

Is transparent hugepage support on or off on these CoreOS machines?

I have a number of CoreOS servers that will be running some database workloads that highly recommend Transparent Hugepages be disabled. However: ~$ cat /sys/kernel/mm/transparent_hugepage/enabled ...
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48 views

Installing LTTng-modules 2.5.4 on CentOS 7

I am trying to install LTTng-modules 2.5.4 on CentOS 7, by building it from source because CentOS 7 is unable to install this package from RPM. Running "make" to build package contents results in the ...
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56 views

strace not showing anything for thread at 100% 'system' CPU

I'm having difficulty with my Python app going to 100% 'system' CPU time across multiple threads for up to 10+ seconds. My (limited) understanding is that 'system' CPU time is time spent in the ...
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1answer
33 views

Linux kernel behavior when dealing with colliding subnets

I'm using openconnect to connect to my office VPN. They push some pretty crappy/aggressive routing rules allocating ALL of the private IP address spaces >.< After I connect to my office VPN, my ...
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3answers
1k views

Why CPU spent time on IO(wa)?

I know wa (in top) measures the CPU time on waiting for I/O. Many articles say that. But I am confused that, based on 2 knowledge points: if a process uses a system call to read disk, the process ...
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0answers
20 views

How do processes stuck on uninterruptible sleep state get cleared upon reboot? [closed]

While processes stuck on an uninterruptible sleep state (i.e. TASK_UNINTERRUPTIBLE waiting I/O from a defunct device) cannot be killed by signals sent by root via the kill command, more often than not ...
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0answers
42 views

CPU usage of server extremely low and webpage load time high?

On a weekday at a time where very few use the optimized website on the server, the time for the page to completely load excluding 3rd party advertisements is about 0.6 seconds to 1 second. Now when a ...
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2answers
25 views

Can I use kernel modules on Amazon HVM/PV instances?

It's a perfectly stupid idea, I know. But I want to test one of my older projects, which includes kernel module (Netfilter extension) on a virtualized cloud-y instance. Will it be possible for me to ...
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0answers
22 views

How to show per-process amount of non-swappable memory?

I am using a VPS which has, unfortunately, stringent limits on maximum total size of non-swappable memory for all processes in the container; this limit is called in kmemsize in OpenVZ. I would like ...
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0answers
103 views

Random machine hangs with NFSv4 on CentOS/RHEL 6.5

We have an in-house "compute farm" with about 100 CentOS (free re-distribution of RHEL) 5.7 and 6.5 x86_64 servers. (We are in the process of upgrading all the 5.7 boxes to 6.5.) All these machines ...
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0answers
53 views

strongSwan on Angstrom

My problem is to establish a VPN tunnel between cRIO 9068 and a Cisco router. To accomplish this task I was planning to install strongswan on cRIO (opkg install strongswan). I have installed it on ...
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2answers
70 views

AWS fails to resize an RHEL64 instance upon launch

I'm using AWS to boot up a RHEL64 instance but the disk is failing to resize to fit the volume I've selected. Here's the scenario: I Launch a running instance from the Marketplace AMI ami-517eec6b ...
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0answers
47 views

linux system slab cache proc_node_cache usage too large

My system run java program only, at some time the memory usage increase very quickly to a very hight percentage: memory usage of java : PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ ...
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0answers
30 views

Purpose of sysctrl tcp timeout unack field

Could some one let me know the purpose of sysctrl tcp timeout unack? If i modify this value from 300 t0 400, what will be the impact. /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_unacknowledged ...
5
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1answer
207 views

Why does strace return so many execve calls with ENOENT return code?

I wanted to use strace to see what was happening when I do `hadoop fs -ls ', so I ran the command: strace -f -e trace=execve hadoop fs -ls /stg which resulted in a lot of output like this: [pid ...
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0answers
36 views

Can you use isolcpus or other kernel parameters in AWS?

We have recently started using cpuset for certain network intensive processes and I want to set a system-wide default for everything else so it doesn't use the designated cores. After a few seconds ...
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0answers
424 views

rcu_sched self-detected stall on CPU on Debian server

My server is online since October 2014. Debian GNU/Linux 7.6 uname -r 3.10.23-xxxx-std-ipv6-64 It was working fine till last night. Last night it bacame unresponsible. I rebooted it from dadata ...
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0answers
44 views

Server crashes because of SMP

My web server is crashing every few days unless I disable SMP with "nosmp" parameter in Grub config. It is not an hardware failure because the problem persists after moving everything to a new ...
0
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1answer
63 views

High %sys utilization in Nginx cache node

We set up Nginx with Lua (openresty bundle) to be a local caching node to our file sharing server, we seperated files to chunks "50MB each" (by this method) and store them in cache to increase its ...
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2answers
70 views

Can a Linux Kernel be shared between two operating systems?

Quite simple question. I am working on a project to have multiple operating systems (all linux) on the same machine using btrfs subvolumes so that the user can boot to the environment they are ...
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3answers
95 views

Networking in Linux KVM

I want to know if there is any way other than using linux bridges to interconnect interfaces from two virtual machines ? Since I am trying to run private spanning tree implementation in virtual ...
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0answers
36 views

Analyse kernel crash file on Ubuntu server 11.10

I am experiencing random crashes on a Ubuntu 11.10 server, and for the time being the system can not be upgraded, even tho this distro is very old. uname -r 3.0.0-12-server I've set it up to get a ...
0
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0answers
55 views

Centos 7 cpu frequency below the minimum value

Hyeverybody,I have 2 similar Dell PowerEdge r720 server wih the following configuration: CPU: Intel(R) Xeon(R) CPU E5-2630 v2 @ 2.60GHz RAM: 64GB OS: Centos 7 I have noticed, that the in recent 2 ...
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0answers
130 views

Must kernel-version of Ubuntu linux-cloud-tools match the kernel version of linux vm on hyper-v?

Microsoft's recommendations for installing Ubuntu VM's on Hyper-V (note 5) include installing kernel-specific versions of the linux-tools and linux-cloud-tools packages. However, there are also two ...
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145 views

“error: ‘PATH_MAX’ undeclared” when trying to make menuconfig

I have an OVH cloud VPS with Ubuntu 14.04 64 bit server. I needed linux headers which OVH does not provide by default, so I found some tutorials on how to compile the linux kernel from source using ...
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182 views

PCIe card memory regions ignored on linux kernel 3.13

On my system, with kernel 3.13.0-32-generic (Ubuntu Server 14.04.1 LTS) installed, one of the PCIe boards in the system (06:00.0) is having it's memory regions ignored: Interrupt: pin A routed to IRQ ...
0
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0answers
242 views

What are the pros and cons of large receive offload (LRO) vs generic receive offload (GRO)

I have been debugging a scenario where an ESX vmware host is communicating with a virtual linux machine via a virtual switch using TCP/IP. After a congestion event the vmware host is waiting for an ...
3
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1answer
67 views

Nginx uses both writev() and sendfile()

I noticed that when serving images Nginx is sending images using both writev() when called from a browser such as Firefox, but uses sendfile() to send the image when wgetting the image. Any idea why ...
0
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0answers
136 views

Apache hanging - FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME

We are running Apache 2.2.15 on a CentOS 6.6 server [2.6.32-504.3.3.el6.x86_64] (with FastCGI PHP, mod_pagespeed, mod_spdy, etc) all the most recent versions. Today we had a case where on one of our ...
1
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1answer
289 views

Running multiple ubuntu (or other distro) inside Docker containers on CoreOS, is this efficient?

From what I have read I believe CoreOS to be a bare-bones Linux distribution which essentially facilitates running Docker containers that contain any applications or services that you require. From ...
2
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0answers
45 views

What are the advantages NAPI before the IRQ Coalesce?

As known there are two approach to avoid some overheads of hardware interrupts in highload networks, when there are too many hardware interrupts, that switching to them takes too much time. It is very ...
0
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1answer
39 views

IPSEC stack low speed

I am working on Openswan IPSEC Implementation for Linux-kernel 2.6.35.9 My concern is when i do speed test using IPSEC kernel Images and without running IPSEC service i get speed of 40Mbps and ...
0
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1answer
63 views

My server boots a kernel I don't recognize

On my dedicated server I'm running Debian 7.5 as an OS. I have installed OpenVZ for amd64 architecture to use the benefits of virtualization but after successfully installing it (following these ...
0
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1answer
318 views

Warning :mounting fs with errors, running e2fsck is recommended

Linux server will hang and when I restart it will take around 2 hours to come up and resume normal operations. I checked the system log files and found mounting fs with errors, running e2fsck is ...
0
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1answer
132 views

How to disable ipv6 support in Linux entirely?

We are currently setting up a some local network servers to run in a full ipv4 network. I can be sure, that this network don't have ipv6 support, and never will. Next to that, partially because of ...
1
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1answer
134 views

Windows multicast NLB with Linux clients

I'm (on behalf of a client, anyway) having some troubles with Linux accessing a multicast NLB cluster hosted on Hyper-V (waiting for more information on what version, but I don't think the version is ...
3
votes
1answer
91 views

Unidentifiable processes under Redhat Linux

Upon issuing a ps ax command on a server I see the following processes that I can't identify. Googling them yields nothing useful. Does anybody know what these are or how I would track them down? The ...
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0answers
84 views

INFO : task events/2:69 blocked for more than 120 seconds

I'm using RHEL 6.3 running on VMWare vsphere and aproximatively every month there is this error message and application running above hang until I restart the server: "echo 0 > ...
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1answer
317 views

enable fanotify on oracle redhat linux kernel 2.6.39-400

As a newbie in linux environment, I am trying to install clamav daemon, which is clamd, on oracle redhat linux 6 kernel EUK 2.6.39-400. It needs to have fanotify enabled in the kernel. As I see there ...
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101 views

The default value for vm.dirty_background_ratio

Wondering why the default value for "vm.dirty_background_ratio" from Linux Server (CentOS and Ubuntu) is set to 40. Is this just a recommendation for safety? Or is there any particular reason why? ...
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0answers
106 views

linux not replying to an arp request

I am running linux 3.14 on a system with 2 interfaces. on the first interface, i can access our local network. on the second interface, arp packets come in but linux doesn't send out reply. is it ...
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0answers
140 views

Utility to list and modify kernel modules loaded during system startup

How do I list all kernel modules loaded while system startup? Is there a user space utility to list and modify the modules loaded during system startup? I am working on RHEL6 Desktop and RHEL6 ...
5
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1answer
78 views

View full program command line arguments in OOM killer logs

Is it possible to view full program command line arguments in OOM killler logs ? What I see now in /var/log/syslog is Memory cgroup out of memory: Kill process 29187 (beam.smp) score 998 or sacrifice ...
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1answer
69 views

Apply patch to custom kernel manually [closed]

I compiled a RHEL based kernel with a script. I've come to know that our version of kernel is vulnerable to attack and we need to apply security patches. ...