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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In what order does kernel reclaim memory?

As far as my knowledge goes, when Kernel requires more memory for allocation for the processes it does a few things before entering OOM state. Such as freeing SlabReclaimable, Dropping annonymous page ...
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Why does the Linux kernel not use rust?

I have heard that the Linux Kernel uses rust. I don't know much about the programming language except that it has the potential to run faster than C. According to websites Rust is more safe than C ...
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PCIe kernel module UIO PCI GENERIC

I build petalinux 18.03 for PICe application for zcu102 Xilinx card. When I debug simple PCI read/write I get an error saying he can't load this driver from Linux file system: uio_pci_generic So the ...
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Creation of Kernel Modules

I have to create a linux driver for the first time and I have some questions which I don't found convenient answer. My goal is to create a PWM driver, I already succeed to create a driver and work ...
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Kernel doesn't seem to be signed for Secureboot. (linux-image-5.17.5-76051705-generic )

I've been trying to get secure boot enabled but don't manage to do it. I have installed shim and Grub correctly with sudo apt install shim-signed && sudo grub-install However, when I boot, I ...
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What is Virtualbox's "vboxdrv" module?

I have a tainted kernel and at least currently journalctl -k | grep taint points to the specific module: localhost.localdomain kernel: vboxdrv: loading out-of-tree module taints kernel. localhost....
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Stuck in GNU GRUB v2.04 loader

I just started my computer and this is what I see : GNU GRUB version 2.02~beta2-9ubuntu1 Minimal BASH-like line editing is supported. For the first word, TAB lists possible command completions. ...
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im trying to install backports in my kali linux but im getting an error while using the code line " make list-defconfigs"

im trying to install backports in my kali linux but im getting an error while using the code line " make list-defconfigs".screenshot I have done both apt update and upgrade and search ...
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Why can't update my linux kernel to the latest version 5.16?

Install the latest linux-image: sudo apt install linux-image-5.16.0-0.bpo.3-amd64 List all my linux-image after installing. sudo dpkg --get-selections | grep linux-image linux-image-5.10.0-10-amd64 ...
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OOM still happens even though there is sufficient memory

env set: arm64, DDR 1GB. Linux version 4.14.181 ,Linaro GCC 8.2-2018.08~dev. The initial memory status is as below, and after running for a while , oom happens. # cat /proc/meminfo MemTotal: ...
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Run Wireguard as a client on Win10 with WSL2

When attempting to run a Wireguard client in a Docker container or on WSL2 itself you will run into issues such as: 2022-04-27 17:15:45,035 DEBG 'start-script' stderr output: [#] ip -4 rule add table ...
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How could Linux kernel driver get output from the other module or command?

I'm writing a new driver that need to get some output from the other kernel driver. For example, Driver A need to get the physical dma address from Driver B. I think, I could write a ioctl char device ...
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KASAN config in 32 bits architecture?

I am trying to compile linux kernel (version 4.4) with KASAN support on a 32 bits machine, but i can't enable it. It seems that it depends on 64 bits architecture only. So my question is about the ...
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Who loads bridge.ko modules when Linux system starts?

When my CentOS Linux system starts, bridge.ko and ebtable_broute are loaded, I'd like to know which module is loading these modules. [root]# lsmod | grep bridge bridge 266240 0 stp ...
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Are There Softirq Race Conditions?

Softirq's are merely a function stored in struct softirq_action. The softirq_vec is an array of 32 of these softirq_action's. The element number specifies the type of softirq based on the enum... ...
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Explanation about free, available and buff/cache and how to find what process is buff/cache saved for in a server in the command "free -mh "

I see explanation for free -mh as: free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is ...
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Is vmalloc() allocate bytes of memory which is virtually contiguous maps to memory area from different physical pages?

vmalloc(size) allocates a memory of size long which is virtually contiguous but the physical mapping would not be contiguous. Does that mean the the virtually allocated size long memory actually lies ...
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OpenSUSE not showing up on EFI boot menu after Tumbleweed update (Btrfs with LUKS)

The issue: A few days ago, I updated OpenSUSE tumbleweed and didn't remember seeing anything out of the ordinary. However, when I tried to reboot my computer it went into rEFInd fine but when OpenSUSE ...
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Is there any way to achieve prioritized IO operations in Linux 5.xx?

I run a lot of long-lived and io-heavy processes in addition to interactive processes on my machine. Unfortunately, they slow the interactive operations down to a crawl despite my best efforts. I ...
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How to build the kernel correctly on its tinyconfig configuration?

I have A68N-5600E motherboard. Through the Live Linux image, I got a list of downloaded modules for this PC. amdgpu gpu_sched joydev radeon i2c_algo_bit drm_kms_helper ahci crct10dif_pclmul ...
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Linux kernel BUG: scheduling while atomic: swapper/0/0/0x7fff0001

I'm running Arch Linux, kernel 5.17.3 (though this issue has been happening across many versions.) Every couple of days, I get random complete system freezes. The kernel logs vary, but they most ...
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Does "generating /boot/initrd.img-5.4.0-107-generic" mean that my kernel is being recompiled?

Under Linux Mint 20.1, some updates will print the following (or something similar) in the "Details" window: generating /boot/initrd.img-5.4.0-107-generic Does that message mean that my ...
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Finding default process scheduler

Where in the Linux code, I can find the default process scheduler at the time of launching a process. For a running process, chrt shows SCHED_OTHER. On the hand, in various websites, I see that the ...
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get all the files to be compiled from .config file

I have an old kernel and I didn't manage to get the toolchain to cross compile it. So I decided to upgrade this version of the kernel. My question is how can I know all the files(source, blobs and ...
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Out of memory on "Loading initial ramdisk" after kernel upgrade (4.15 to 4.19) on Ubuntu 18

I'm trying to upgrade my kernel to 4.19, because I need to run some benchmarks that require it (with some kernel options turned on). I'm completely stuck as to why this isn't working. I did two ubuntu ...
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linux kernel freeze

I am using linux kernel 4.19 on intel (icelake) based server. Sometime immediately after linux boot (at the login prompt) it get stuck(once is 50 reboot or so). It is not responding to anything on ...
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Increase size-limit of messages written to /dev/kmsg

I have a custom initramfs whose logging output I wish to redirect to /dev/kmsg. The Kernel I am using is 5.10.52 However, I realized that I cannot write more than 992 bytes to /dev/kmsg at once. Is ...
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What is special about GNU/Linux 3.2.0?

I am staring at the output of: % file -b /lib/x86_64-linux-gnu/*.so | grep ", for" | colrm 1 130 | sort -u =5018237bbf012b4094027fd0b96fc22a24496ea4, for GNU/Linux 3.2.0, not stripped 9f21d,...
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Restrict users switching from one to other user

I have 5 users in my linux machine (user1,user2,user3,user4,user5) and my requirement is each user except user5. Remaining 4 users able to switch only user5. But they don't want to switch any other ...
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Debugging remote reboot/shudown/boot/startup problems without console access

What are the options for collecting debugging output from boot/startup/shutdown on a remote host where one does not have console access? I'll give my specifics in case the context matters, but I've ...
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Which function in the Linux kernel creates the segments?

I'm working on a problem for my Master's degree and I'm trying to track down how a segment is created and how it calculates the checksum. I've located a function called tcp_sendmsg() but, even by its ...
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Why does the /boot folder contain only older kernel stuff after upgrading the kernel?

Following instructions at https://github.com/microsoft/WSL2-Linux-Kernel I successfully built and installed a new kernel: uname -rs returns Linux 5.10.102.1-microsoft-standard-WSL2+. However the ...
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Requesting suggestion on debugging Linux kernel freeze

We are working on custom embedded Linux board with power pc based SOC and display panel. We are debugging an issue where during video playback Linux kernel just freezes, it doesn't respond to even ...
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23 votes
3 answers
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Has Linux always separated User and Kernel space?

I was thinking back to my introduction to programming recently and remembered writing a C++ program that deliberately read and wrote to memory addresses at random. I did this to see what would happen....
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Running Raspberry PI buildroot image in qemu

I am trying to build a linux image for raspberrypi3 with buildroot and run it on qemu. Once the make process is done i can copy the sdcard.img file into a SD card and correctly run the OS on a real ...
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Accessing sys/kernel/debug through SSH via sshfs

Following scenario: We have an embedded Linux system 'A' for which we want to debug some driver and device registers through /sys/kernel/debug, aka using FUSE's debugfs. Our test software is running ...
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Network unreachable while tftp on a virtual machine. What config should I add?

I'm trying to build a minimal kernel where tftp works. I'm using busybox for initramfs and I'll be running the kernel on an arm64 virtual machine. The command for getting file is tftp -g -r ...
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Linux multiprocessors support

I am reading the following paper. In the paper, the authors argue that Unix/Linux "has struggled for a decade to support multiprocessors in a single node" in the last paragraph of the first ...
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Boot customized Ubuntu image over PXE via Serva encounter Kernel panic

Background I had make a customized img on Ubuntu 20.04 via dd command from a usb disk driver. Using serva as pxe server like serva tutorial. It is successful completion boot over pxe on official ...
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A simple global keyboard shortcut handler

Yeah, I know there's actkbd which allows to assign global keyboard shortcuts which will work everywhere including the text console and a graphical session but I don't want to run an extra daemon (long ...
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Why does grub kernel parameter slub_debug=P crash the system with some software?

I've observed that when passing slub_debug=P (together with FZ) as a kernel parameter to grub, KDE Plasma will crash when I close the electron-based note taking software Obsidian. I don't understand ...
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4 votes
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How come Fedora ignores `module.sig_enforce` kernel parameter if SB is enabled but Arch does not?

I recently secure-booted Arch and Fedora on my RTX3050 equipped laptop. As is the common knowledge, I had to sign my Nvidia modules on Fedora for the kernel to load them. However, I find that same is ...
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APT says that the linux headers, modules, images, and extra modules aren't needed anymore and should be removed

I just finished updating the linux kernel via APT and restarted my machine. Then I checked for more updates and it said this: The following packages were automatically installed and are no longer ...
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statvfs returns invalid information

My eMMC partition is ext4 formatted and has about 100MB. When I issue statvfs() on that partition, I get huge return value for f_blocks field of struct statvfs. struct statvfs { unsigned long ...
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update-initramfs does not fully create initrd for new kernel

I seem to be having a bizarre problem installing a new custom kernel. update-initramfs fails during dpkg -i with: update-initramfs: Generating /boot/initrd.img-5.15.7-hardened1-test1 find: ‘/tmp/user/...
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How does RAM get divided into Kernel Space and User Space

I understand that with Linux, RAM gets divided into kernel space and user space. Kernel space is reserved for running the kernel, and user space applications should not have direct access to the ...
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Too many open files error, but only when accessing through a mounted disk

I am having a problem where once I try to copy something from a mounted unit on a windows dfs server (Windows server 2012), I get the "Too many open files" errors from linux, but ONLY if I ...
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What is the best way to back-up the Linux kernel before performing a kernel and device tree update?

Is this as simple as duplicating the directory /boot to /boot~ before using dpkg to apply the updated Kernel ? So if the systems is bricked then all I would need to do is put the SD card into another ...
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Can't compile Kernel module with KBUILD_CFLAGS_MODULE

I'm having trouble to compile kernel modules with KBUILD_CFLAGS_MODULE with new kernel. The compiler shows me a weird error. Such builds used to work with my older kernel (5.5) but does not work ...
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How to update the kernel for a live CD Linux image

I have a liveCD ubuntu Linux iso image. I need to update the kernel of this image. I've tried to get the iso on a host Ubuntu system and move the compiled kernel and the modules from there to the ...
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