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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Can I compile Linux kernel with -Ofast?

I want to know if compiling the Linux kernel with -Ofast is: Worth it. Supported (what level of optimization do the kernel writers take into account?) Secure. The question arised because ...
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Poor performance from a Wireless network card

I'm new to Stackexchange, so I apologize if I don't get quite how the platform works yet. Regardless, I believe you're all more than capable of helping me out here. Currently running Linux (let me ...
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Kali Linux - Bluetooth HCI error don't let live system boot

Hello community i have a bootable USB Drive (usb2.0) with Kali Linux 2017.1 x86 on it, i used rufus for doing this couple years ago, i was using Kali Live system to test some of my java programs with ...
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How to read MCP2515 registers from application using sockets?

I have a MCP2515 CAN controller connected to SPI and I am using Sockets to send/receive CAN frame(using sendto/read) in application. How do I read the CANCTRL register of MCP2515 from the application ...
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Remove ECC warnings in system log

How can I disable these warnings about ECC? I don't have ECC memory and so disabled it in bios also but it still prints it. [ 4.697057] EDAC amd64: Node 0: DRAM ECC disabled. [ 4.697061] EDAC ...
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How to access the wi-fi driver folder on my hard drive while installing Arch linux?

I recently tried to install Arch linux. When I booted into Arch linux setup from bootable usb drive, I tried the wifi-menu command to connect to my mobile hotspot but it just said to use netctl. When ...
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How to update the driver used by the Debian Linux kernel for my processor?

A few months ago I installed Debian 10 on my laptop, I have already managed to use it regularly for my daily activities, so I am starting to customize my settings. And started by validating the ...
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What is kernel headers that can be used in userspace? Do their signature or interface differ than the headers in different directories?

It might be a incoherent question about kernel headers as I don't have clear understanding about it and where and how it is used. I think it might get flagged down. My question has 3 parts: I think ...
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Revert installed mainline kernel using systemd for booting

I installed a the new 5.6 mainline kernel with ukuu. Unfortunately it breaks my Wifi. How can I go back to an older mainline kernel, which I know works well?` I use pop_os which boots with systemd.
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PCIe Kerneldriver DMA writes to incorrect addresses [migrated]

I'm currently writing a PCIe kernel driver for linux kernel 4.19. A FPGA (Arria 10) running an Intel DMA IP is connected to the Linux CPU (i7-6700TE) via PCIe Gen 2. I want to run an upstream DMA ...
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Is /usr/src a valid location for a custom kernel?

While learning how to build and install a custom kernel (for kernel hacking), I came across a contradictory statement. In this StackExchange answer, the author states: in the following ...
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About the mmap field in mm_struct

The mmap field in mm_struct is a pointer pointing to the list of vma areas of the respective process. So, my question is, whether this mmap is a virtual address ? If yes, how does kernel access it (...
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How can I get the 'root' boot arg in kernel space?

I am writing a driver and I need to know what disk/partition contains the root filesystem. This can be viewed from userspace using: cat /proc/cmdline root=/dev/mmcblk0p1 How can I get the value of ...
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__report_bad_irq not getting hit

I am stucked in one issue, in which i am getting __report_bad_irq callstack inconsistently. AFAIK, whenever we have 100000 unhandled interrupts this stack kicks in. Output from cat /proc/irq/128/...
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Does Linux kernel since version 5.0 have a CR0 protection?

In kernel versions 2.X through 4.X, you could have easily overwritten the 16th CR0 bit in kernel modules with: write_cr0(read_cr0() & (~ 0x10000)); This way it used to remove the write ...
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Navi 14 works with kernel 5.4 and 5.6 but not 5.5?

I managed to get Ubuntu installed on a MacBook Pro 16-inch. I compiled kernel 5.5.11 from source with some patches to get it to run. Mostly everything works except the onboard dGPU doesn't seem to ...
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Retrieving pointer to an existing i2c device class

I am working on communicating with an i2c slave device using loaded /dev/i2c-1 master driver that is loaded and working in my linux computer. This slave device needs multiple synchronous writes as ...
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How are the kernel daemons running automatically?

I have written my custom init (PID 1) script. In that script I have just mounted the necessary filesystems, but if I run ps aux the list is similar to below: / # ps aux PID USER TIME COMMAND ...
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use of copy_user_page() method while implementing COW(Copy on write)

I want to implement copy on write on the heap region. Are there methods that I need to modify in the kernel level code?
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Process hung on futex system call

A DB software(Aerospike) that I had been using since a long time without any problems has now suddenly stopped working(hung) and I'm not able to find out the cause. Given below is the strace output: ...
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Why DTBO fails on load and says no symbols in root of device tree.?

I am trying to build a DTBO from a dts file. I have a few questions here. I get a warning when I build this - /opt/poky/2.7.3/sysroots/x86_64-pokysdk-linux/usr/bin/dtc -o dtb -o phyDriver.dtbo -@ ./...
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How to flash SPI NOR and read back from the SPI Nor - Microzed Zynq from Uboot?

I am trying to read the kernel image from the mmc card and flash it on the SPI Nor flash. My kernel image is uImage only. So, I read the kernel image from mmc card and put that into the memory ...
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Need explanation of arguments to kthread_create()

I am currently reading Linux kernel development By Robert Love. While reading about threads, I came across kthread_create() function which takes several arguments and spawns a kernel thread ...
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Is my Touch Screen Digitalizer supported?

I am hoping that the "10-point capacitive multi-touch"-digitalizer of an 11" convertible notebook is supported by the Linux kernel, but I have a feeling that it probably isn't... how can I determine ...
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Drivers completely messed up after the last Ubuntu update [closed]

Ma laptop (Dell Vostro 7590 with a i7 9th gen) was working completely fine with Ubuntu but the last update from Ubuntu completely messed my drivers. After the reboot I had no sound. I fixed this ...
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Low latency vs normal kernel?

I am new to this world, and I want to make and record music with my new Linux installation, as I have found marvellous applications. I have seen some youtubers recomending to install the linux-...
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Why is the integer value of SIGRTMIN (first real-time signal) 34 and not 32? [duplicate]

Examining the output of kill -l command $ kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2 13) ...
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How does the linux kernel support dns changes for resolving domain names?

In linux, the dns servers are configured in /etc/resolv.conf, without going into userspace implementations, how are changes to this file supposed to propagate to the many consumers of domain names?
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Create a kernel crash without using “/proc/sysrq-trigger” [duplicate]

Is there a way to create a kernel panic without using echo c > /proc/sysrq-trigger option?
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Is “/proc/<pid>/map_files” include mapped file of all tid or just include mapped file of tid=pid only?

There is /proc/pid/task/tid/maps file but no corresponding /proc/pid/task/tid/map_files.
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How does Linux kernel works irrespective of the platform it is on?

What I specifically want to know here is: Irrespective of the underlying hardware it is on how Linux kernel manages to work on all different PCs. Or in general how any kernel can (Microsoft's NT ...
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Modules installed when building the kernel end up in a different directory than the kernel version

I have recently upgraded from 5.0.4-gentoo to 5.5.6-gentoo. After some problems and kernel panics, I was able to fix the boot such that the new version was loaded and grub config got updated. ...
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How does the TCP/IP protocol differentiate between clients?

If we create a listening socket it will return us a descriptor (let say root descriptor) and we are binding this descriptor to a address. Whenever a new client connection is available the root ...
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LEDs don't trigger on CPU activity

I'm trying to set some triggers for the LEDs on an embedded board (Rock960). They work with heartbeat and mmc1 (main drive) and none of course, but I haven't been able to get any of the cpu<i> ...
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how to delete specific kernel and clean up dir /boot

I am trying to recover from attempt to remove a specific kernel ... I can login to Ubuntu using previous kernel release shown on login GRUB menu ( avoiding the newest top most kernel which I am trying ...
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How to get directory structure and inodes from files recovered through debugfs

Somehow system update at hosting VPS site deleted my cpanel. I tried to recover files on Centos using debugfs. Command used 1. debugfs /dev/ploop40383p1 2. lsdel - gave me the nodes that were deleted....
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polling for GPIO in user space

I wrote a USB driver a few months ago for an ARM STM32 board that provides access to the pins,on Linux. I can set or reset the pins on my board using sysfs interface. In the Interrupt section, the ...
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Linux read() system call sampling rate, task scheduling & RT_PREEMPT

I am working with a Measurement Computing PCIe-DAS1602/16 DAQ: https://www.mccdaq.com/pci-data-acquisition/PCIe-DAS1602-16.aspx with Linux device drivers written by Warren Jasper: https://github....
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Linux hangs at first start with black screen, the second is ok

Everytime I start Linux the system hangs with a black screen and no keyboard, then I must reboot with magic sysrq, and then the boot completes correctly. At the end of kern.log I got (this is only a ...
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mdev doesn't seem to be working on reboot

Our Linux Kernel is 3.10 running on an embedded mips processor with busybox. The init script has - echo "/sbin/mdev" > /proc/sys/kernel/hotplug mdev -s We have a rule to rename a network ...
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High kworker CPU usage on idle embedded system

I am working on an embedded device where the kworker stays at high cpu usage when the device is idle. iostat output: bash-4.3# /intflash/iostat Linux 4.9 03/05/20 _ppc_ (2 CPU) ...
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Does fstat require disk access on Linux/ext4?

Linux Kernel 5.3 Consider the fstat syscall defined as int fstat(int fd, struct stat *statbuf);. Is disk access required for the fstat syscall on ext4? I did some research related to it and find out ...
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What do the Block Device Capability flags mean?

Linux block devices in sysfs have a capability file, partly documented here. Well, one is documented. Looking in genhd.h as it suggests, there are others. Is there any documentation on them, or does ...
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1answer
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Kernel throws error while writing to the character device file in 4.9.82-ti-r102 debian 9.3

I created the device file under /dev folder successfully, but writing to that device file makes kernel to throw following error messages. Message from syslogd@beaglebone at Feb 26 15:40:10 ... kernel:...
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How to delete or shrink compiled kernel installation directory and still build an external module?

I am having trouble building external modules after compiling the linux kernel on an external device. It is the 4.19.103 kernel with the real time patch-4.19.103. My onboard storage disk is <3Gb ...
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SysRQ+B (boot) not working but O (turning off) is

For some reason, my Linux machine will properly turn off when striking SysRq+O, but won't reboot as expected when doing SysRq+B. Both of these ones show up in the help message (with SysRq+H) and all ...
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Kexec: Can installer available in initramfs access (to copy) a file in disk storage

I am trying to migrate from one linux(embedded) say host to another say guest(without pendrive). kexec -l <installer> --initrd=< initramfs.cpio containing actual guest installer> I have ...
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How to filter kernel parameter changes from kern.log?

I'm trying to add a use case to my SIEM where it triggers when kernel parameter change happen. I did some digging around the internet, but can't seems to find any method for filtering them from rest ...
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1answer
20 views

Scan PCI-Devices beginning root bridge

I am now looking for countless hours in the linux/pci.h and all connected files to understand how the PCI can be securely scanned (read-only) and then picking a pci_slot when the device matches. ...
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What application manages the consoles

With Alt + Fn you can switch between virtual consoles in most Linux distributions. What application handles the switching of consoles and how? I suppose it has to read the keyboard input before all ...

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