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Questions tagged [linux-kernel]

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 to block non vlan traffic for an ip address on linux

I have a vlan created on a Linux vm and assigned ip address to it.I would like to block all incoming traffic to the IP address that is not coming from the same vlan I would still like to able to send ...
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Does iptables rules have control over raw socket packets?

A program I use generates some TCP connections using raw packets mode. Let's say that I executed those two commands: /sbin/iptables -A INPUT -s 8.0.0.0/8 -j DROP /sbin/iptables -A OUTPUT -d 8.0.0.0/8 -...
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Using a compressed initrd when pxe booting

I'm using netboot/pxeboot with grub. menuentry "Install Ubuntu 20.04" { set gfxpayload=keep echo 'Loading vmlinuz ...' linux /tftp/vmlinuz ip=dhcp netboot=nfs nfsroot=10.0.0.20:/data/...
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Soft-RoCE (RDMA over converged ethernet) over bonded ethernet interfaces?

I am having a hard time finding any information at all about wether it's possible to use the Linux Kernel RXE driver (software RDMA over converged ethernet) with bonded ethernet interfaces (using ...
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Page cache in Kafka

We are receiving alerts for kafka memory utilization in our kubernetes cluster and analysing it seems that most of the memory is page cache. I am aware that kafka uses loads of page cache for IO ...
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System failed, please help me interpret last console messages (screen capture)

This server runs several processes of satellite imagery, it has 256GB of RAM, 12TB disk, 64 CPU cores Intel(R) Xeon(R) Gold 6226R CPU @ 2.90GHz. It should not fail with this charge but it does ...
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3 votes
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Bind mount one container FS tree into another for debug or ephemeral containers?

I'm testing out k8s debugging features including debug pods and ephemeral containers, and I just can't work out how to properly map a "target" pod's file system into the debug container. I ...
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VirtualBox on linux: hangs on __lock_acquire on Fedora Core 35

VirtualBox (VirtualBox-6.1.x86_64) has for sometime been useless on my workstation (Linux FC35,kernel is 5.16.12-200.fc35.x86_64+debug: but the issue existed previously on FC33). The GUI starts, but ...
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Precipitous page allocation failures leading to system crash

We run a platform that uses Linux bridging to filter traffic and also logs that activity to a MySQL server. Occasionally we have an issue where the unit will experience very high latency, and leading ...
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Using iptables for SSH brute force protection

10: Limit new TCP connections per second per source IP 53 /sbin/iptables -A INPUT -p tcp -m conntrack --ctstate NEW -m limit --limit 60/s --limit-burst 20 -j ACCEPT 54 /sbin/iptables -A INPUT -p tcp -...
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Packet loss in PGSQL query leads to very long recovery time

We have a seemingly complex network issue that I have been struggling with for a while and wondered if anyone had any thoughts We have a number of servers sitting in AWS London and another set of ...
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Why do I see many "kernel: vif ...: Guest Rx stalled" / "Guest Rx ready" messages?

Since upgrading a Xen host that also is a node in a pacemaker cluster from SLES15 SP2 to SLES15 SP3, I see these messages roughly every 30 seconds, and I wonder: What are these messages telling me? ...
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Debian: Kernel update using APT - reboot required to take effect?

Suppose I update the kernel of a running Debian system using apt-get upgrade linux-image-amd64 to a higher minor version number (e.g., 5.10.10 to 5.10.11). Do I have to reboot the Debian server in ...
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Should Hard drives always set the rotatinonal flag in /sys/block/<device>/queue/rotational?

Folks, AWS exposes HDDs in their D3 instances (https://aws.amazon.com/ec2/instance-types/d3/) as nvme drives and these drives DON'T set the rotational flag as they're supposed to (https://lwn.net/...
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Sed issue!! i tried to trigger this command cat test.txt | gf xss | sed ‘s/=.*/=/’ | sed ‘s/URL: //’ | tee testxss.txt

i tried to trigger this command cat test.txt | gf xss | sed ‘s/=.*/=/’ | sed ‘s/URL: //’ | tee testxss.txt but getting error as sed: -e expression #1, char 1: unknown command: ' sed: -e expression #...
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Why I get "cache" in the output of `ip route get`?

I'm using kernel 5.11.0 and in the ip-route manual [1] it can be read: Starting with Linux kernel version 3.6, there is no routing cache for IPv4 anymore. Hence ip route show cached will never print ...
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atftpd service start and removal error

I am facing error while doing apt --fix-broken install I searched on google but no luck. After this operation, 5,120 B of additional disk space will be used. Do you want to continue? [Y/n] y ...
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Selective Suspend in Linux?

In order to find the reason why my system is rebooting instead of suspending, I would like to suspend my devices one by one to find the faulty one. Is there a way to do this in Linux? I searched for ...
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Linux kernel firewall logging - how to change where it goes?

I'm using an iptables based firewall, Firehol. It's great but it generates a lot of logs. These logs go (a) to /var/log/syslog and (b) get echoed onto the virtual terminal. This makes it very hard to ...
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Openstack ( using libvirt image type as LVM )- Very low IOPS

As part of the base line testing, able to see qcow is providing much higher iops compare to the LVM. Ideally it should be the reverse ( as per my knowledge gathering ) Kindly please advise me on how ...
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DELL R320, Xeon E5-2450 v1, Oracle Linux 8 marks clocksource 'tsc' as unstable, random crashes under load

I recently acquired used Dell R320 with Xeon E5-2450 v1, all firmware's are updated to most recent versions using Lifecycle controller. On boot dmesg reports: microcode: microcode updated early to ...
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Couldn't load target `NOTRACK':No such file or directory

I am trying to add a IP table rule. iptables -t raw -A PREROUTING -j NOTRACK But when I am executing this I am getting below error: iptables v1.8.4 (legacy): Couldn't load target `NOTRACK':No such ...
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Can't run docker-container 'failed to create endpoint frosty_varahamihira on network bridge'

When I try to run the hello-world docker image I get the following error: ubuntu@ubuntu:~$ sudo docker run hello-world docker: Error response from daemon: failed to create endpoint frosty_varahamihira ...
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perf gives high copy_user_generic_string and clear_page_rep

I am building a server in c++ that reads a lot from disc. When recording with perf I get this report: 28.20% server [kernel.kallsyms] [k] copy_user_generic_string 18.14% server [...
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Kernel TCP tuning for buffer overrun and packet collapse

We have a Nginx+Ruby application where the data between Nginx and the application are interfaced through a socket. As part of performance improvement, when we analyzed the netstat statistics on the ...
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Forwarding ipv6 link local destined traffic not working

Setup: VM (eth0) -> hostveth -> ContainerVeth eth0 and hostveth are in VM network namespace while containerveth is in different namespace sysctl ipv6 forwarding and iptables FORWARD chain are ...
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1 vote
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BTRFS on RHEL8 - compiling kernel module or making userspace tools work

Context I recently installed RHEL 8 without realizing that it no longer supports BTRFS. Unfortunately, I have 4 disks in BTRFS RAID10. I don't have enough space on my other disks to hold the data ...
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2 votes
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Changing your kernel in AWS appears to break boot sequence (grub config issue?)

Using Ubuntu 20.04 on AWS (ec2), I wanted to change my kernel from AWS to a generic one. When I try it the suggested way with changing the Grub Config, it stops the machine. This is because Jibri (...
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Advice required for sending STP BPDU traffic between tap interfaces connected by common bridge

Need advice for the bridge tap interface to run stp traffic. created the tap interface and bridge   Have come across stp BPDU is consumed by bridge. i'm running the scapy on the host, however i'm not ...
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Cannot boot from initramfs (unable to switch root, sysroot directory is empty)

Okay, so I have a problem with Fedora 34. More specifically, I have a problem with a custom built image that is part of the services that we deliver. The Problem The problem has to do with initramfs. ...
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No Crash Log on centos 5.13 kernel

My System has multiple kernel installed on it. when the server is booted on default kernel the crash logs appears in /var/crash on each crash but when system is booted on another kernel which is ...
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Disk IO issue with high Page writeback

I have been trying to figure out what's going on with some of our servers. These are KVM hosts that have 5 -8 VMs. RAM >= 64GB, 10 - 20 cores. These are running Ubuntu 18.04 LTS 4.15.0-142-generic ...
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Load Testing CPU utilization that occurred while executing at the system level

Is there a way to load test CPU utilization at the kernel level? Output for sar 09:00:01 AM CPU %usr %nice %sys %iowait %steal %irq %soft %guest %gnice %idle ...
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Connectivity issues with 127.x.x.x series [closed]

Asked this in network-engineering in stack exchange and was redirected here. I have a couple of servers with the below config server1: eno1: 127.15.0.1/16 scope global eno2: 5.0.0.1/24 server2: lo: ...
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Server has continuous beep alarm when I reload the kernel

Here is the situation: I have a Lenovo ThinkCentre M900 with Linux CentOS 7. I tried to do a kernel load (kexec -l + kexec -e), and it works fine, with one problem. As soon as I enter the kexec -e ...
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CentOS 8 compiling kernel 5.13.7 BTF Error

I'm compiling Kernel 5.13.7 for Centos 8.4.2105 I've got the below error MODPOST vmlinux.symvers MODINFO modules.builtin.modinfo GEN modules.builtin BTF: .tmp_vmlinux.btf: pahole (pahole) is ...
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Why am I seeing overlimits in TC statistics?

I configured my linux servers with tc (TBF) using the below parameters: rate 1Gbit burst 1000Kb lat 200.0ms Now, when I'm testing Iperf between this server and another server as iperf client, I'm ...
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3 votes
1 answer
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Setting CPU frequency to hardware minimum limit - will it harm the hardware?

I'm running on a Intel Celeron N4120. I can easily set the CPU governor for all 4 cores to powersave using: for n in {0..3} do sudo cpufreq-set -g powersave -c $n done Now, using cpufreq-info I ...
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Understanding buff/cache and tmpfs relationship on a read only filesystem with no swap

We have a really strange bug where a Yocto operating system running on a Raspberry Pi will 'lock up' because of disk IO wait. Scenario: operating system runs read only and has no swap there is a ...
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IPv6 multipath routing with configurable weight

With Linux kernel 4.14, when I add IPv6 multipath routes with weights (10 & 30), they are getting added with same weight '1'. IPv4 route does not have this issue. I checked with exact same steps ...
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2 votes
2 answers
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Why does my Linux Kernel have missing directories / files that are crucial for ip_tables to run?

as mentioned in the header - my Linux Kernel seems to be missing files / directories that are crucial for iptables to run properly. I'm able to temporarily resolve this by reinstalling my kernel, but ...
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Google Cloud Platform - Ubuntu Pro - Quota format not supported in kernel

I cannot get quota to work on Fresh copy of Ubuntu Pro mount -o remount / quotacheck -avugm quotacheck: Scanning /dev/root [/] done quotacheck: Checked 19045 directories and 94713 files ...
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How do routing rules from IPTables, IPVS, and NFTables get ordered from a precedent perspective, in the Linux kernel?

The Linux kernel has the ability to route traffic using nftables, iptables, and ipvs. Ive collected 3 related questions here, in order to generally ask the broader overall question of how ...
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Centos 8 CLI failed to start Switch root . “failed initrd-switch-root.service” [exit code]

I have Centos 8 Cli version installed , due to power off the OS starts directly in emergency mode without starting root user . I have attached screenshot here The OS is on VMware Hypervisor esxi 6.5 ...
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Linux: How to setup dns server via dnsmasq and connect a second machine with it?

Setup: I have two vms running: prime and second. On the prime dnsmasq is installed. What I need to accomplish: Setting a second(machine) so it connects and looks for domain names on the dns server. (...
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Disk extremely slow on VM

Environment: Hypervisor: VMware ESXi, 6.5.0, 4564106 Guest OS: Debian 9.5 | Kernel: 4.19.0-0.bpo.16-amd64 Guest resources: RAM: 40GB, CPU: 16 cores Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz, Disk: ...
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Is it possible to upgrade from centos 6 kernel 2.6.32-754.25.1.el6.x86_64 to 5.12.1 version?

You are currently using centos6 kernel 2.6.32-754.25.1.el6.x86_64. I'd like to upgrade to 5.12.1 to take action against the vulnerability in this version, and I'm asking if it's possible. If it is ...
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Influence source address selection to same destination with multiple interfaces

I have a system with two network interfaces, both connecting to same default gateway. I want to load balance the connections to the same destination IP made from the system across both interfaces and ...
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1 vote
2 answers
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What is the state of AppArmor network rules in the latest kernel?

I decided to give AppArmor a try and while it works great at restricting file access, signals handling etc., it completely ignores any network rules. It doesn't complain about anything, but it also ...
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What triggers a "*** Guest State ***" register dump from the linux kernel?

Prefix: There is no kernel crash. Something, rarely, is triggering Guest State, Host State, Control State register and other debug variable dump to kernel log. The system in question is running many ...
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