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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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Available options for real-time Linux (Centos 7) and their relation to one another

I'm looking to expand and also get more current information from the question asked here. I have a requirement for real-time behavior that has is sub-millisecond and am now exploring what my options ...
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Optimizing Linux for desktop responsiveness without thirdparty kernels

The default linux kernel config (at least in Ubuntu and Arch) is not as optimized for desktop responsiveness as linux-ck or Zen Kernel. The difference between those kernels and the default one is very ...
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1answer
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Getting sector number from inode or address_space mapping

In am trying to understand how to calculate a sector number from an inode in the ext4 filesystem. Therefore, I am reading ext4_mpage_readpages function. About the function: During a read request, if ...
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kcompactd high CPU usage

kcompactd is spiking while we are PUTting a file using FTP to another host, and the transfer rate is dropping. top - 18:39:59 up 31 days, 6:23, 4 users, load average: 1.15, 0.42, 0.32 Tasks: ...
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1answer
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How to get around R_X86_64_PLT32 error when bisecting the Linux kernel

When bisecting the Linux kernel to find a bug (in my case between v4.4 and v4.9), I'm encountering the following build error: RELOCS arch/x86/boot/compressed/vmlinux.relocs Unsupported relocation ...
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27 views

Can't load kernel

I'm a Mint user. I was trying to solve a problem, which is that when I suspend my PC I can't resume. I found on stack exchange Ubuntu an answer saying to use "ukuu" in order to upgrade the kernel. ...
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1answer
26 views

Read keyboard inputs in Linux

I am making a Ruby program so I can play different sounds when a key is pressed. Key A will make different sound from key S and so on. I want to get raw inputs rather than using some ruby gems. For ...
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1answer
48 views

Binary executable file with write permission get READONLY from vim

First I know that use vim to write a binary executable program is not recommended. So, I don't want to talk about its rationality here. I have a binary program, with permission 755(owner is root), so ...
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Linux kernel module address randomization

I'm booting the same 16.04 Ubuntu server image (4.4.* kernel) and checking where modules are loaded with cat /sys/modules/[module_name]/sections/.text. After every boot I get different text segment ...
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1answer
57 views

Realtek RTL8821 Ethernet card not detected by Kali Linux

When installing Kali Linux, an error message appears during the "Detect network hardware" step. The message says: "No Ethernet card was detected. if you know the name of the driver needed by your ...
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1answer
40 views

unlink/rm target of an open symlink

I've come across an issue where processes that load symlinked .so files crash if I update the .so while the processes are still running. I have long-running processes that load shared libraries (.so)...
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Boot problems on Ubuntu 16.04 (elementary os) with kernel 4.4.0-145

After a recent update on my dual boot hp laptop with secure boot disabled, whenever I switch back to linux (from windows 10) on the default kernel (4.4.0-145) the boot process gets stuck in this loop ...
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Need to recompile module ideapad_laptop, how? [on hold]

I found that ideapad_laptop doesn't have my laptop, causing wifi to not work. I need to edit and recompile the file. The file is here. Now I want to recompile that file and the other files it needs so ...
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1answer
21 views

How to manually mount the virtual file systems, to copy MTD partitions

Linux version 2.6.26.5, ARM Linux Kernel on embedded device, NAND-based device. I'm at Busybox rescue shell (ash), with restricted command set. How to manually mount the virtual file systems, to copy ...
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1answer
63 views

Why is kernel module blacklisting so weak?

There have been several times in the past year or two where I have tried to blacklist Linux kernel modules (either through blacklist.conf or kernel command line parameters), and yet it hasn't worked - ...
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1answer
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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
35 views

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? [closed]

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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0answers
27 views

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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20 views

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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37 views

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
73 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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52 views

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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1answer
26 views

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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1answer
42 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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24 views

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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16 views

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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33 views

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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Linux kernel debug - no source code

I am debugging the Linux kernel. It is running on a guest virtual machine (qemu/kvm) while I use the Eclipse debugger on the host for debugging. The remote debugging works well but I don't see any ...
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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
91 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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1answer
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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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1answer
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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
70 views

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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31 views

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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32 views

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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0answers
23 views

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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24 views

What is the purpose to clear the kernel log buffer

What is the purpose to clear the kernel log buffer ?? why we do that?