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Questions tagged [linux-kernel]

Questions about Linux kernel and Linux kernel related topics eg. implementation details such as system calls, kernel customization, etc. For Linux user space topics which do not involve kernel details, [linux] or distribution tag are more suitable.

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Does the kernel address region in user page tables need to be updated in an 64 bit system?

In 32 bit systems with more than 896 MB of RAM it is obvious, that the mapping of kernel addresses need to be changed because of kernel virtual addresses and the non-continuous mapping. But how is ...
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1answer
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How is the Linux git repo related to other distribution git repos (such as Ubuntu)?

I am trying to build a custom version of my Ubuntu kernel, and want to apply a patch that I see on the main Kernel tree. I know that Ubuntu development happens in these repos: git://git.launchpad....
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How to view ICMP Redirect Logs

I have read on multiple sources that there is are logs for rejected ICMP redirect messages, one of them being "Understanding Linux Network Internals: Guided Tour to Networking on Linux" By Christian ...
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How can I implement multiple kernels into bsd/Linux? [on hold]

Like on the lowest level, on multiple cpu machines I want oop code organizing things in the fashion of multidimensional binary trees.
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kernel TCP/IP implementation - about accept queue

I'm recently learning the TCP/IP implementation in linux kernel(version 4.4), and got really confused about the accept queue. I know there is a queue in struct inet_connection_sock which is called a ...
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I can boot directly from guest kvm?

I install linux as guest on kvm, there is way to boot from that linux when i open my computer? like live usb.
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What is led_cdev? And how to use it in Linux kernel (directly)?

I'm trying to debug a kernel panic on an embedded device with no access to serial output. The device has a small notification LED which is supported by a driver in the Linux kernel. So, I thought ...
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1answer
47 views

“Forcing” a kernel panic from the terminal on Linux

I'm using Solus 4.0 (in a VM) and trying to make screenshots of "typical" kernel panic output ("BSOD"). The init system in Solus is systemd. I tried the following commands in the terminal without ...
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ebtable rule to disable packet(other than BPDU) flood/forward on bridge device

The configuration has one bridge device and two ports attached to it. The requirement is to disable flooding or forwarding of any packet from bridge device to other associated ports. How to achieve ...
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overall HIGH CPU utilization, but top is not showing process which is contributing to that spike

Below is the output of a top command, which is showing "57.6%us, 24.0%sy" overall cpu utilization at a particular moment, but there is no process which is contributing to this spike of cpu usage. ...
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1answer
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How large are the “watermark” memory reservations on my system?

swappiness This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. A value of ...
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make: *** No targets. Stop. error when trying to build Linux Tree Directory

I just start contributing on Linux Kernel. I am following this guide https://youtu.be/LLBrBBImJt4?t=1052 . Up to that point I did required changes. Run the script to check for the code and it was ...
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Where is CONFIG_HZ defined?

I'm in the middle of reading the whole Linux 5.0.7 source code, and I've noticed something strange. I'll refer to linux as the parent directory here, correct me if the community uses some other naming ...
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36 views

How to disable TCP checksum validation on Linux?

For some reason, I want to disable TCP checksum validation on my Linux host. Is that possible to disable it?
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Is there a way to find out which process is setting a Linux kernel parameter to an invalid value at runtime?

I have set the kernel parameter fs.inotify.max_user_instances to 100000000, but it is automatically getting set to 1256 after a while. Is there some way to figure out which process is setting it to ...
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1answer
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What made the Linux kernel so good during its early years? [closed]

What I'm trying to find out is, what made the Linux kernel catch on during those early years (1991 - 1994-ish). I know that the open-source idealogy and Unix-base helped it, but so was Minix, 386BSD, ...
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Kernel-core fail

I use Fedora 29 (xfce), and today it's starts to break my browsers. Appears to me the message: "unexpected error" "the system encountered a problem and recovered" but, it's been happening even me ...
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Is linux mount propagation asynchronous to the mount call?

I have two processes in different mount namespaces. They have a shared directory bind mounted to /mnt/share. The "master" uses MS_SHARED propagation for the mount, while the "slave" uses MS_SLAVE. ...
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1answer
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Can I change LIO SCSI Disk Vendor name

I'm using LIO for SAN scsi. The shared disks shown as LIO-ORG at client side. Example; [root@testing ~]# lsblk -S NAME HCTL TYPE VENDOR MODEL REV TRAN sdc 4:0:0:0 disk LIO-...
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Does each directory under `/sys/fs/cgroup/` represent a cgroup hierarchy, or a controller?

Does each directory under /sys/fs/cgroup/ represent a cgroup hierarchy, or a controller? (I assume it represents a cgroup hierarchy in the following, because multiple controllers can be mounted to ...
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1answer
88 views

Why does Linux have two data segments, one for user mode and another for kernel mode?

Linux have (in addition to other segments) a user data segment and a kernel data segment. When the CPU is in user mode, Linux loads the segment selector of the user data segment into the DS register. ...
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1answer
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Does chroot need any special kernel support?

docker is said to be a steroid version of chroot. Does chroot need any special kernel support, e.g. namespace, cgroup? Does docker rely on chroot? I ask this because "Docker is not virtualisation: ...
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What is “a light-weight namespace container” created by systemd-spawn?

man systemd-nspawn says systemd-nspawn may be used to run a command or OS in a light-weight namespace container. In many ways it is similar to chroot(1), but more powerful since it fully ...
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Trouble with Legacy interrupts on new CPU

A legacy (IntA) interrupt works on an old CPU under Linux, but fails under the same Linux OS with a newer CPU in that system. I'm unsure if the problem is in the BIOS or in the Linux driver, as both ...
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Does Linux uses Segmentation (in addition to Paging)? [duplicate]

As far as I know, Linux uses Paging to allow processes (and even the kernel itself) to access memory. And through paging, the CPU can prevent a process (which runs in user mode of course) from ...
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How can I view threads for a running process that is creating threads?

I made a very small program that creates two threads: #include <pthread.h> #include <stdio.h> #include <unistd.h> void *start() { printf("Am a new thread!\n"); ...
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uboot Flattened Image Tree decompilation

i have run into a problem when trying to configure the bootargs for my embedded linux system. The device tree is compiled into the same image as the kernel. It includes bootargs ( /chosen/bootargs ). ...
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1answer
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What is a docker container from Linux's point of view? [closed]

A docker container is a concept understood by docker daemon. What is a docker container from Linux's point of view? You can stop, kill and destroy a container. Is a container itself a process? Is a ...
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1answer
47 views

Phony USB hubs in Linux

Using Ubuntu 18.04, with my desktop motherboard I obtain: $ lsusb -t /: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M /: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=...
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How to configure embedded linux kernel so that the file system is visible on the host linux

I am using a powerpc, and after building and flashing the linux kernel on the device I can see the file system. But if I try to create a user or make any changes they get erased and resets to default ...
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How to set default kernel to boot from?

I have two linux images so far 4.19.0-2-amd64 and 4.19.0-kali3-amd64. It starts with Debian as default but I want some packages from Kali. To group Kali packages, Debian separate in the Application ...
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Which process (kernel thread) is doing the actual compression for zswap?

I can imagine actually two locations: In the kernel space belonging to the process whose ram is being swapped in/out From [kswapd0] However, digging into the kswapd source (mm/vmscan.c, init/main.c),...
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Encouraging the CPU to perform out of order execution [migrated]

I am attempting to exploit the meltdown security flaw on Ubuntu 16.04, with an unpatched kernel 4.8.0-36 on an Intel Core-i5 4300M CPU. First, I am storing the secret data at an address in kernel ...
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Configuring virtio vsock for android (aosp)

I want to use virtio vsock for communication between host machine and vm. My host is running ubuntu. I understand by default virtio vsock module is enabled for ubuntu so I don't need to do any ...
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What is the purpose to clear the kernel log buffer

What is the purpose to clear the kernel log buffer ?? why we do that?
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1answer
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What you wish to remove or add to linux kernel? [closed]

I was wondering what or how we can do to develop a better Linux kernel or variant (if necessary). What problems does Linux have and how could they be solved or if Linux needs some feature? ...
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1answer
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Debian Linux kernel versioning

On a Debian Stretch distribution, if I run uname -a, I obtain: Linux index 4.9.0-8-amd64 #1 SMP Debian 4.9.144-3.1 (2019-02-19) x86_64 GNU/Linux If I run dpkg -s linux-image-amd64 | grep Version, I ...
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2answers
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Mediatek MT7630e not working on Linux 5.0.2 & 4.20

Under Elementary OS Juno, I am trying to use Mediatek M7630e WiFi, which doesn't work. I know that in Fedora 29 with the officially supported Linux 4.20 it does instead, even if not perfectly - I ...
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1answer
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How do the kernel and processes communicate?

In Linux there are various ways for inter process communication, for example, shared memory, (named) pipe, socket, message queue. What are equivalent or similar ways in which Linux kernel and ...
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UBI layout volume not found

I am following Bootlin's embedded Linux training which aims to put an embedded Linux system on an Atmel SAMA5D4 Xplained board (theory slides, practical lab instructions) and I am stuck a putting the ...
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journald flooded by kernel messages

My journald log was at some point filled up with kernel messages like this. Mar 12 05:03:53 workstation.mydomain kernel: FAT-fs (sdd1): FAT read failed (blocknr 1785) Each followed by a message ...
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Own boot parameter in Linux kernel gives no outprint (Homework)

The task is to write a own boot parameter in the linux kernel that activates printk under the kernel initiation. The Linux kernel version that is edited is 4.16.7 (buildroot 2018.11.2) and my ...
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2answers
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Change CPU count on live Linux VM

Is it possible to change the number of VCPUs on a KVM virtual machine on Linux without stopping it first? The Linux kernel has calls for addition and removal of CPUs (CPU hotplug in the Kernel) for ...
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Are bind mounts just another mount of the same filesystem?

I'm reading What is a bind mount? I tried mount --bind -o ro / /mnt, then I get the folowing two lines in /proc/self/mountinfo: 23 0 0:21 /ARCHLINUX / rw,relatime shared:1 - btrfs /dev/sda rw,...
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Does the Linux kernel need a file system to run?

My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file ...
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1answer
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Permission denied when cd to symlink'd dir in /tmp that is 700 and owned by regular user

Question: Why am I not able to cd into a symlinked directory with 700 permissions, owned by a regular user, as root, when I am able to change into the directory itself? Example: ttucker@plato:/tmp# ...
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1answer
57 views

Root shell in system filesystem with GRUB

I'm learning about GRUB and, after search for a while, I tried to get a root shell changing the kernel load string: /boot/vmlinuz-4.9.0-8amd64 root=UUID=e8485edc.... ro single to /boot/vmlinuz-4.9....
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How do I build the mainline kernel with all default Ubuntu modules?

My normal way of building a mainline kernel has been: $ sudo apt build-dep linux $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git $ cd linux $ make localmodconfig $ make -...
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Are WiFi, audio, video modules included in the kernel?

I have an old netbook based on WM8880 SoC (https://laptop.fossee.in/) which used to run lubuntu 16.04 (customised heavily by the fossee team) via Uboot bootloader fairly well, one fine day it said I ...
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ath10k QCA9377 doesn't load wifi unusable [closed]

The wifi load dead slow in ath10k QCA9377 i tried using various other adapter it works fine only on this it is dead slow (not a useable speed) is there is any way to load wifi in a usable speed? *-...