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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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Can't run any snap using linux 4.12 : snap-confine has elevated permissions and is not confined but should be

I am using Ubuntu 17.04 with linux kernel 4.12.2 which I installed using the software ukuu (Ubuntu Update Kernel Utility). Every time I try to run a snap in my system when I am using this linux ...
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Kernel config for keyboard special LEDs

I'm building a 4.9 linux kernel (which is working great) for my T460s. The F1 key has a led that shows if sound is muted. I can't get this LED to work even when enabling all kinds of LED-relevant ...
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Linux 3.x fails assigning PCI BAR memory

I got an IBM x3850 type 8864 machine, I can successfully boot using a 2.6.32 kernel but when I try to use a 3.10 kernel or newer the kernel fails to initialize all PCI slots (I can fix this (manually),...
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Kernel config diffs - better way to maintain

I maintain one Linux distro (LEAF) with multiple kernel targets, so it needs to have multiple kernel configs (one reference config + usual patch files for other targets). But this adds headache on ...
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How to create Linux Kernel Headers from Linux Kernel Source?

I'm working with Tiny Core Linux and attempting to install Vmware Tools, which of course needs the Kernel Headers :-). It does not appear they have the Kernel Headers readily available in a package, ...
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838 views

How to read the output of the show-memory-usage SysRq?

I couldn’t find any (recent) documentation on reading the output of the show-memory-usage SysRq (Alt+SysRq+m). So what can one learn from looking at it? Here is an example output form my box (Kernel ...
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Why are block sizes limited by page size in Linux?

In many (all?) file systems that Linux uses, including ext2/3/4, the maximum block size is the page size of the architecture Linux is running on, ie. 4KiB on x86. Why is there this limit? Might this ...
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What is the relationship for the NX bit among the four-level page tables?

I would like to scan all executable pages in the linux kernel. The most easiest way is to walk through the page table to identify all PTEs(Page Table Entries) which clear the NX bit. However, ...
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What is the modern way to develop a Linux auditing kernel module?

I'm new to Linux Kernel development, and I am now assigned a task to develop a Linux kernel module, which can monitor the network, filesystem, USB and serial ports. I am aware of the things like ...
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Dell XPS 13 9350 wifi dying with Broadcom BCM4350 and 4.8 kernel

Launchpad report: for all those with the same problem, please subscribe to this report I opened in Launchpad so that it can gain some traction. I've been using Ubuntu 16.04 with kernel 4.7 for some ...
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How to switch static drivers like switching kernel module drivers?

I have a linux embedded device that I need to switch between USB file storage gadget driver and USB Ethernet gadget driver at runtime. The approach I use now is to build both drivers into kernel ...
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Print kernel memory layout

Userland memory layout can be inspected by looking into /proc/self/maps. I am wondering if there is a similar facility allowing to inspect runtime kernel memory layout?
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Centos 7 boot up with custom kernel problem

I have installed centos 7 on virtualbox machine which has kernel-3.10.0-123.20.1.el7.x86_64. I am trying to build Linux kernel from kernel sources. I downloaded the kernel source files from: http://...
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update kernel without restart

Recently Linux got a new feature called Live Kernel Patching, which you means you don't have to restart your system to update kernel. Is there any other kernel which has this feature already or Linux ...
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How to prevent kernel or any broadcast messages from flooding the TTYs?

Because of some hot-plugging issue, similar to what talked of here, the TTY displays show a continuous stream of messages (which are also logged in the /var/log directory). Every text I key in flows ...
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How to create the framebuffer file node?

I'm working with a limited embedded device - Linux environment - that uses a custom DirectFB implementation to draw a user interface in its video output. I would like to exchange this method by a raw ...
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787 views

EDID Invalid on USB DisplayLink Device

I have a Sabrent USB to HDMI adapter which is a DisplayLink device. It's recognized by udl as being a DisplayLink device, yet seems to be rejected/disabled due to having an invalid EDID: [32780....
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Kernel does not detect Hardware / Software or Hardware fault

My Linux kernel (I tried several here from stock 2.6, 3.2 and 3.5 as well as a custom 3.7.3 one) does not detect my synaptics touchpad - or I am too dumb to find it. I looked into: dmesg, lsusb -v, ...
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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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kernel 2.6.35.3 - how to convert .config to defconfig

If you have newer kernel (i.e. > 2.6.35.3) you can create a 'defconfig' from a '.config' by using make savedefconfig But in kernel 2.6.35.3 - does not provide you with 'savedefconfig' target. How ...
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143 views

kexec: relocate_kernel fails

I am not able to get kexec to work. For x86_64 relocate_kernel fails to store information for jumping back. Kexec stops in movq %r9, CP_PA_TABLE_PAGE(%r11). works fine for kernel 4.4.162, doesn't ...
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439 views

Kernel BUG: unable to handle kernel paging request

So I'm trying to run this kernel module on my laptop, and every time I do so, I get a stack trace that looks like this (all the messages might not be relevant to the module). [17539.035247] EBBChar: ...
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How do I upstream a patch into the Linux kernel developed by someone else?

I've recently been trying to upstream part of the Nintendo Switch-on-Linux patchset, but it appears that the original developer must sign off on each commit. Do I need to ask the original developers ...
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748 views

Explain output of cat /proc/vmallocinfo

What does this output represent after doing cat /proc/vmallocinfo. I know, this gives mapping of virtual address space of kernel. But want to have in-depth understanding. Questions What are actual ...
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What is the maximum processor frequency that Linux could run on?

Theoretically, if an extremely fast computer could be built (100s of GHz or even terahertz), what is the maximum frequency that could be expressed in the variable used by the scheduler allocate cycles?...
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Which Linux kernels include a particular bug fix?

How do I know which Linux kernels have merged a particular bug fix? For example, as mentioned in this question: Kernel Bug 198357 - iwlwifi: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware ...
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How to combine linux kernel and initrd without compiling?

I know that it's possible to extract from a linux kernel the embedded initramfs cpio. I want to know if the reverse operation is possible; i.e., given both a compiled kernel and initramfs archive, how ...
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312 views

Loading a kernel module at run time using “compatible” property of device node in device-tree

If I know the "compatible" property string of a device(from the device tree), can I use it at runtime to load the corresponding kernel driver module? I do not have access to the driver source. I am ...
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Hooking sys_execve on Linux kernel 4.6 or higher

Kernels lower than 4.6 use assembly stubs to harden the hooking of critical system calls like fork, clone, exec etc. Particularly speaking for execve, the following snippet from Kernel-4.5 shows entry ...
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How to handle exceptional page when allocating contiguous cache pages in Linux

I have a kernel module code which allocates contiguous cache pages. I use radix_tree_for_each_contig(). Here is the partial snippet of the code. radix_tree_for_each_contig(slot, tree_root, iter, ...
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Limit on number of virtual interfaces in linux?

I am running some automated tests with docker containers, and this includes creating a lot of veth interfaces (about 2 per container, ~1000 containers). Whenever I do this, the system shuts down. ...
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How to run kernel in debug mode and wait for KGDB with Virtualbox and Kali Linux?

I am trying to debug a Linux kernel using Virtualbox, but I cannot get it working. Here is what I've done. Compile Kernel with the following configuration CONFIG_HAVE_ARCH_KGDB=y CONFIG_KGDB=y ...
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151 views

MSI interrupt in serial driver

This is a more general question: I have a RS485 PCIe card in my system (PERICOM_PI7C9X7954). The driver for it is in 8250_pci.c. It configures the PCIe interface. However, it doesn't use the MSI ...
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How to install Linux 3.2.40 headers on Synology DS214 with DSM 6.1?

Since I'm tired of cross-compiling and already have a working (cross-compiled) gcc on my Synology DiskStation DS214 with DSM 6.1, I'd like to install the Linux headers of the Linux version running on ...
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343 views

Is it normal that a modalias matches various devices?

Recently another user asked why they were loading the fjes module. While I was trying to understand that question, I realized that Linux is also loading the same module for me. Now, this is the ...
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Kernel messages on console

I just got the following messages on the console: Message from syslogd@andromeda at Dec 5 12:50:47 ... kernel:page:ffffea003ae93000 count:3 mapcount:0 mapping:ffff9986dc372810 index:...
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Difference between syscalls and raw_syscalls events?

AFAIK different linux tracing tools gather information from /sys/kernel/debug/tracing/events directory where different events are logged. Can anyone explain the difference between "syscalls" event and ...
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578 views

Total available physical memory from /proc/meminfo not adding up

I'm trying to account for the available physical memory on a Linux box through /proc/meminfo (output provided below). Accounting for current free memory, user-space physical usage, kernel data ...
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Device Tree Overlay fragment notifies and loads children twice

I have the following device tree overlay fragment, and when it's loaded, spidev is added twice: fragment@0 { target = <&fpga>; __overlay__ { #address-cells = <1>; ...
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Linux kernel: Bigger swap-in chunks

I have been quite happy with suspend-to-disk. But getting more and more RAM, this is not really working as well as it used to. Suspending TO disk works fine: It takes a minute or 2, which is what I ...
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327 views

Linux boot hangs

I have been having a problem recently with one of my computers getting Linux to boot. I mainly use Manjaro or Linux Mint and so far both have been running into the same problem at boot. The following ...
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813 views

Kernel panic - not syncing: Attempted to kill init! during early boot

I am getting Kernel panic - not syncing: Attempted to kill init! during early boot on my Fedora Linux system. Root and home filesystems cannot have been mounted since both are encrypted and I have ...
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828 views

Changing Console Resolution in Core (not Tiny Core) Linux

I have recently got Core Linux, and am having trouble setting the resolution to 1920x1080 (my native resolution). I have not got a /etc/default/grub directory, nor have I got a UI. My question is, how ...
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461 views

How to compile custom kernel for Raspberry Pi

I'm trying to run the Ubuntu 14 Raspberry Pi ARM image in QEMU, and for that I need the kernel that matches the version used in the image. If I mount the image and run file vmlinuz I see: vmlinuz: ...
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FIPS mode, signature verification failed

I am building a kernel with FIPS mode on. I followed most of the procedures described on Red Hat documentation here. I also created a hmac signed .vmlinuz file. After installing dracut-fips and ...
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Enumerate valid values for mknod

I have access to an embedded device which has a bunch of block/char files under /dev. However, this is not a satisfying description of the hardware, because since the firmware is shared with small ...
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Virtualbox and GPU Pass-trough: Device with host PCI address already attached to this VM

I have server with several GPUs. My idea is to attach them to different VMs in order to use that VMs in CUDA (or OpenCL) calculations. My setup: CPU: Intel Xeon E5-2670 GPUs: 1 x Radeon HD 7970 $ ...
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Kernel - Measuring the rate of timer interrupts

I am working on optimizing kernels of my boxes for telephony, which involves (among other things) adjusting the HZ rate and the preemption model. Initially the kernel was compiled with the default ...
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Linux Angstrom can't start without serial cable plugged

I'm using the Altera Cyclone V Soc dev Kit and Linux Angstrom provides by rocketboards (http://rocketboards.org/foswiki/Documentation/GSRD141) Kernel is : 3.10 LTSI Linux can't start if any serial ...
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What is the difference between Local timer interrupts and the timer?

When I do cat /proc/interrupts on my multicore x86_64 desktop PC (kernel 3.16) I see this: 0: 16 0 IO-APIC-edge timer LOC: 529283 401319 Local timer interrupts When ...