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Questions tagged [kernel]

In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources (the communication between hardware and software components).

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Session “NT Kernel Logger” failed to start

I have encountered an error on windows server 2012 recently. Session "NT Kernel Logger" failed to start with the following error: 0xc0000022 More Details: LogName: Microsoft-Windows-Kernel-...
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yum reinstall installs two kernels

As you can see below, there might be (as far as I understand) two kernel versions being installed. Also I get "grubby fatal error: unable to find a suitable template" the reinstall ends ...
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Using ftrace to spy on files being created?

We are in this scenario: https://stackoverflow.com/questions/7304826/how-to-debug-a-multithreaded-hung-process-in-linux When we try to look at a rogue process (which is consuming 100% CPU) then it's ...
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Linux Kernel Mode Vs User Mode [migrated]

I'm trying to better understand the process of switching from user mode to kernel mode on linux systems. When a process requires access to the low level HW/restricted memory spaces, does it issue a ...
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Toggling an interface causes static ipv6 address to be deleted whereas ipv4 address stays. How to make ipv6 address also stay? [duplicate]

I'm working with kernel 2.6.32. I have set a static ipv4 and ipv6 address on my machine. ifconfig eth1 eth1 Link encap:Ethernet HWaddr 00:50:56:AB:8D:A1 inet addr:10.5.175.254 Bcast:...
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how are all/default/interface configuration influencing each other?

On the following kernel configuration path: /proc/sys/net/ipv6/conf/ we can configure each network interface in the following way: we can specify what configuration to follow for all interfaces we ...
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Why the kernel wasn't updated to 4.4 on Ubuntu 14.04? Other related questions [closed]

I had a task to update only kernel to the latest version on Ubuntu 14.04 VPS. What I did: apt-get update apt-get install linux-virtual reboot It updated from 3.13.0-24 to 3.13.0-163. 14.04.x ...
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Cron PHP sessionclean hangs invoking oom-killer

This morning one of our Linodes (18.04.1 LTS (GNU/Linux 4.18.16-x86_64-linode118 x86_64)) crashed. From the syslog I can see that cron task PHP cleansession got stuck around 36 hours ago: Dec 15 23:...
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2answers
122 views

/proc/sys/net/netfilter/nf_conntrack_count extreme drop when reading /proc/net/nf_conntrack

I have very busy Web servers, and wanted to introduce some analysis to see what kind of traffic present. Namely, total number of all connections, number of time waits, established connections, udp and ...
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1answer
59 views

Does a pod in Kubernetes inherit every kernel settings from its pod?

I'm trying to see if my pods are using tcp_keepalive_time. When I ssh into my node and run sysctl -a I see that there is value for tcp_keepalive_time, but pods don't have them when run the same ...
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395 views

Why is MemAvailable a lot less than MemFree+Buffers+Cached?

I'm running a Linux workstation without swap and I have installed earlyoom daemon to automatically kill some processes if I'm running out of RAM. The earlyoom works by monitoring kernel MemAvailable ...
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How much does FreeBSD accept_filter actually improve performance in a modern world?

I recently learned about FreeBSD's accept_filter socket option which can allow a worker process to avoid context switching by, for example, waiting until a full HTTP request is received with accf_http:...
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60 views

Enable systemd-coredump for NixOS/Linux

I'm trying to enable systemd-coredump for NixOS/linux, and I'm trying to set the following: echo '|/run/current-system/sw/lib/systemd/systemd-coredump %p %u %g %s %t %e' > /proc/sys/kernel/...
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Linux Bonding with 2x10G LAN poor performance in kernels after 4.13.x

Here is our setup a DELL server with two 10G LAN ports and our old kernel 4.13.4 serving static video content using nginx (~8000 active connections) with the bandwidth of around 15.5G (1.2Mpps) on ...
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1answer
100 views

Documented size of Linux kernel partition sector size in bytes

My primary question is to authoritatively see if the block size used in sector counts: /sys/block/<disk>/<partition>/size is in fact 512 B, or if this can vary. I thought this would be ...
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168 views

How to keep a specific version of an old kernel while still allowing updates?

I need to keep an old kernel in Fedora: kernel-4.14.18-300.fc27.x86_64 But I still want the latest kernel updates. 1) A naive approach is to change the installonly_limit=3 value to a high number in /...
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1answer
169 views

How come CentOS is using Kernel without support (EOL Kernel)

Just noticed that CentOS 7 is using Kernel 3.10 which was maintained from August 2013 to November 2017 so it's basically EOL. I know that CentOS doesn't update Kernel versions between minor CentOS ...
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ICMP packet size over 372 are dropped on bond0

i have a target server running on rhel7.4 with kernel 3.10.0-693.11.6.el7 with bond0 and subinterface vlan2001 with MTU 9000 when i ping from a different server which is in a different network with ...
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1answer
225 views

Can I delete folders in /lib/modules/ after calling “apt-get purge”

I've already call apt-get purge to uninstall the old kernels. But some error occured during the purge that caused the folders to be left behind. It said the folder was not empty so it couldn't delete. ...
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1answer
53 views

CPU utilization impact due to granularity kernel parameter RHEL6 vs RHEL7

Following kernel parameters are showing very different behaviour from R6 to R7 and we are not able to figure out why. Any help appreciated. kernel.sched_min_granularity_ns kernel....
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Why in CoreOS Kernel parameter sotflockup_panic is activated?

I looked through different Linux distros such as Ubuntu, CentOS, openSUSE, RHEL, PhotonOS, and Alpine for kernel parameter softlockup_panic. In all of them this kernel parameter is deactivated. # ...
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55 views

Debian server systemd-modules-load.service failed

My debian 8 server got a problem today, all the web services are down and the ssh don't work anymore. I started the server in rescue mode and I mounted the server and tried to understand what wrong. ...
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1answer
788 views

AWS EC2 Status Check says “Instance reachability check failed ” with kernel panic

I went to reboot my Centos 7 instance and then did a start/stop and now I get a status check error stating the instance is unreachable. I created a snapshot and image of the volume and recreated a new ...
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1answer
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Is there a way to override 'nr_hugepages' via boot parameters in kernel 2.6 (CentOs 6.8)

Set vm.nr_hugepages too high in /etc/sysctl.conf and the kernel panic during boot due to not having enough memory. Is there a way to disable this via a boot parameter in grub menu? Tried hugepages=0, ...
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0answers
169 views

Compiling linux-tools tools for custom kernel

I have compile my own RT kernel for ubuntu 16.04 but when i try to use the perf or cpupower tool it says "cpupower not found for kernel 4.4.138-myrt". Then even if i have install the linux-tools-...
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1answer
74 views

Do we need to reboot RHEL Servers, after making changes for control-alt-delete override?

We are planning on disabling the RHEL Server reboot triggered by control-alt-delete. for which we are going to follow the Steps mentioned here. However, that link does not say whether we need to ...
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2answers
23 views

FreeBSD/GNU Linux: should I leave kernel crash dumps enabled or disabled on a production server?

I did a google search on kernel crash dumps, and while I found plenty of information on what they are and how to set them up, I could not seem to get a recommendation on whether they should be enabled ...
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1answer
118 views

module be2net not loaded with define parameter in /etc/modprobe.d/

I want to load the be2net module with the parameter rx_frag_size set to 4096, the default value being 2048. As specified by the documentation I created a file /etc/modprobe.d/be2net.conf with the ...
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1answer
292 views

CentOS 7 Kernel Update

I updated the kernel on our servers from the CentOS default of 3.10.xxx to 4.17.xxx using the elrepo repository. After adding the repo, I installed the kernel-m1 package. Edited /etc/default/grub to ...
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3answers
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Why having more and faster cores makes my multithreaded software slower?

I am experiencing bizarre behavior on scaling a multiprocess/multithreaded C++ application. The application contains 10 separate processes, communicating through Unix Domain Sockets and each one ...
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Is there any modern scalable way to do system call monitoring?

I wrote a kernel module to replace the Linux kernel service routines (e.g. system calls) with security-enforcing code, similar to SELinux or AppArmor, with the main exceptions of ruleset control on-...
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110 views

grub-mkconfig -o would not update grub.cfg

Problem is that when I want to generate grub.cfg to load Xen kernel it just ignore the priority set at /etc/grub.d/. As far as I know grub-mkconfig should put 10_linux_xen in the grub.cfg but it ...
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1answer
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Does the maximum amount of open descriptors in a server include it's children?

I know that Linux limits the maximum amount of open descriptors, usually to 1024. Now say I need to create a server which will handle more than 1024 users, 2000 for example, without tampering with the ...
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2answers
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Prevent kernel messages from appearing in dmesg

Is it possible to prevent kernel messages from appearing in dmesg output? E.g. I am running software that terminates PPPoE tunnels. One of the features it provides is the ability to set custom ...
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1answer
73 views

Is load average affected by lack of memory?

I've read several articles about load average and all explained that the load average is the amount of processes in running/waiting to run state on CPU , so it's actually the CPU's run queue + the ...
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Need to Rebuild Kernel Modules After Kernel Upgrade?

I am using CentOS 7.5. I noticed that as soon as I upgraded from kernel-3.10.0-693.el7.x86_64 to kernel-3.10.0-862.2.3.el7.x86_64. Some of the kernel modules aren't there (e.g. all the modules in /...
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0answers
1k views

Ubuntu Server 18.04 taking very long to boot up

I've installed Ubuntu Server 18.04 as a VM to use as a web server and it's taking very long to boot up. During the booting process 100 seconds go by without any notice of what's happening and then the ...
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0answers
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What does a series @^ in the kernel.log mean [duplicate]

My server crashed today. After a cold reset I looked at the kernel.log and found the following: Mar 14 14:45:07 romulus kernel: [1663261.548575] docker0: port 2(vethfbcd09f) entered forwarding state ...
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3answers
120 views

remove originally installed linux kernel, when custom one has been deployed

How do I remove last, the originally installed kernel? Goal: I am trying to configure smallest possible linux server install (Debian 9) machine which will be running application server (PHP7) in a ...
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1answer
198 views

kernel upgrade in ubuntu 12

I am using ubuntu 12.04.5 LTS server version. The kernel it has is Linux 3.13.0-32-generic x86_64. I need to upgrade it to mainline 4.15 version. I tried many times but i am unable to upgrade. ...
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611 views

How to change I/O scheduler for a disk in ubuntu 16.04?

I am trying to set noop I/O scheduler for my disk. However, I am getting this error, -bash: echo: write error: Invalid argument I checked and found that there is no I/O scheduler option in my disk. ...
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130 views

Unable to forward ftp traffic in the passive mode with higher kernels [duplicate]

In order to accelerate the tansmission speed of ftp, I use a middle server to help transfer data from my pc to my ftp server. This is the script running on my middle server to make such forward work: ...
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1answer
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how to roll back a kernel ubuntu 16.04

I could not find this easily today so I am putting it here for other people, and myself in 6 months How do you roll back a kernel in ubuntu LTS 16.04, answered below
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330 views

Intel graphics i915 chpip (onboard graphics card) in the Kernel not working

I've got a server and that uses the i915 integrated graphics chip from Intel error The error is: [ 3.015087] AES CTR mode by8 optimization enabled [ 3.029401] iwlwifi 0000:05:00.0: base HW ...
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How can I enable a newer (installed) kernel in Debian / EC2

I have an m1.large paravirtual EC2 instance running Debian Wheezy. It appears that I have two kernel packages installed: one 2.6 kernel and one 3.2 kernel. The 2.6 kernel is the one that is enabled ...
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688 views

Cannot update kernel on Ubuntu 16.04 “dpkg: error processing package”

I wanted to update the kernel of the Ubuntu VM I'm using on a cloud host which is stuck in 2.6 right now. I use Arch Linux on my desktop, so I'm used to my package manager giving me kernel updates ...
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1answer
497 views

Slow command execution time in Linux

On superuser guys suggested me to go here. We experience some slow simple command execution time in Linux, possibly related to procfs slowness. Like simple uptime command can take few seconds to ...
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0answers
256 views

l2tpv3 tunnel with local ip in vrf (linux kernel vrf)

On a ubuntu host I have two identical ip addresses configured on two interfaces enslaved to two different kernel vrfs. Here they are: mikle@LabHost:~$ ip link show vrf VRF1401 7: enp3s0f0.1401@...
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102 views

Linux kernel and apache 2.2 performance issue on two different web servers

I have a 2 apache with mod_php web servers behind a load balancer, the OSs are CentOS 6.x. They are supposed to be IDENTICAL. They are supposed to receive about the same requests using round-robin. ...
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226 views

Exec format Error. cxbf.ko from kernel has no modversions, so it cannot be reused for kernel

OS: Red Hat Enterprise Linux Server release 6.9 (Santiago) I was updating RHEL packages and ended with errors like: ERROR: modinfo: could not open /lib/modules/3.8.13-16.2.1.el6uek.x86_64/extra/cxbf....