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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Network IO throttling in cgroups

cgroups allow the user to manage the resource usages of processes or groups of processes. Block IO throttling is supported and works well. Why is it however that network IO throttling (specifying hard ...
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26 views

How would/Should one go about hard-coding a transparent SOCKS proxy into the Linux Kernel? [closed]

I'm trying to build a transparent SOCKSifying router but am having issues with very high CPU usage by the ksoftirqd process. My setup is a TP-Link WR710n router running OpenWRT where I run iptables ...
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1answer
34 views

Linux Server: Too Many Open Files

I have an application running on Linux Server. But server suddenly stopped responding but when I ping from other machine to server it allowed to ping but was not allowing to login into the server. Not ...
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1answer
71 views

Default value of /proc/sys/fs/file-max

I am aware that /proc/sys/fs/file-max defines the maximum number of open file descriptors and can be set on runtime or during boot. However: what is its default value? Checking 10 servers in my ...
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1answer
66 views

Linux: Why does the CPU frequency fluctuate when using the performance governor?

I'm using a Debian 8 amd64 machine for benchmarking. During experimentation, I would like the CPU to operate at a fixed frequency (preferably the maximum possible). This will rule out the CPU clock ...
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4answers
50 views

is /dev/dm-1 a partition or a whole block device?

Is there a way to figure out if /dev/dm-1 is a block device partition or a whole block device? If /dev/dm-1 is a partition, is there a way to find out the path to the corresponding whole block device? ...
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5 views

Unattended build of linux kernel [migrated]

Goal: I am trying to automate the 4.0.4 kernel build to provision it to multiple machines. Since AUFS no longer ships in "extras" package, I am compiling it as well, and then adding via make ...
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39 views

Debian Jessie 8 idle on fresh install always a little too high, shows rcu_sched ksoftirqd kworker causing cpu load

Are the days of 0.0 cpu load on an "idle" server gone? I have another server (centos/redhat) 32GB ram that actually runs apache/MySQL/Lamp, mono, redmine/ruby, and other junk and its still shows me ...
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108 views

sysctl: cannot stat /proc/sys/kernel/exec-shield: No such file or directory

Enable ExecShield protection - ExecShield is security Linux kernel patch to avoid worms and other problems. After Adding to /etc/sysctl kernel.exec-shield = 1 Getting this error sysctl: cannot ...
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80 views

'BUG: unable to handle kernel NULL pointer dereference at' on Google Compute Engine

On a semi-regular basis, I've seen GCE instances freezing with the following error message (from the serial console): g[1375589.784755] BUG: unable to handle kernel NULL pointer dereference at ...
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2answers
87 views

Removing old kernels

My boot partition is full and I can't install new kernel versions. So I tried to remove some old versions like this: get active kernel uname -a Linux Ubuntu-1404-trusty-64-minimal ...
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1answer
56 views

NTP service stopped in centos7.1 linux machine

In our 3 linux boxes centos 7.1, we saw below messages in the logs and then ntpd service got stopped since the offset is more than 1000s. systemd: Time has been changed ntpd[2626]: 0.0.0.0 0617 07 ...
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1answer
79 views

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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1answer
44 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
143 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
115 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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45 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
324 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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71 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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0answers
84 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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144 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
34 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 ...
16
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2answers
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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28 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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51 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
31 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
28 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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1answer
151 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 ...
0
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0answers
86 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
92 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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83 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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40 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
233 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
47 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
670 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
60 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 ...
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1answer
82 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
77 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
115 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 ...
0
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0answers
41 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 ...
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0answers
65 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
172 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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224 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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231 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 ...
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0answers
390 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
77 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 ...
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0answers
226 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 ...
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1answer
378 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
68 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
45 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 ...