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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Yocto kernel build fails with “undefined reference to imx_smp_wfe_optee_end”

I have a yocto build running on several debian und ubuntu machines. Today I started the same procedure on a freshly install debian buster, but the image build did fail during kernel build: arm-fslc-...
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Network bandwidth aggregation

Lets say I have access to two different networks: A and B. My device has two different network interfaces N1 and N2. A has a bandwidth of 5 mbps B has a bandwidth of 3 mbps I want to combine these two ...
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Linux report that lowmem region is more than physical memory available?

I'm running Ubuntu 20.04 64-bit version. I'm starting to learn about kernel programming and I'm now studying kernel VAS. when running a process called procmap by kaiwan on github which is supposed to ...
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Cannot make persistant Insertion of a kernel object (debian) using Insmod

I'm trying to insert the [.]Ko (Kernel Object) file for the on-board GPIO into my Linux kernel which succeeds using the command insmod < file-name.ko > But when the OS/Device Reboots, the kernel ...
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Linux Mint 20.1 Kernel Options

I have just installed Linux Mint 20.1 and I am wondering what kernel I should be using. In the Linux Mint update manager, there are 5.4.* kernel versions, and 5.8.* versions. My active kernel is 5.4.0-...
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running load on volume

Hi everyone here my query i need to run load on a number of volumes of a storage box but those volumes are not presented to the hosts as there are limited host available is there any script or ...
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Linux Kernel vs Distro & Installation process and requirements (ARM vs x86) - How It Actually Works?

Hi everyone (from noobs to geeks and SU!), I am one of the beginners that can't sleep at night if I didn't get it right, so here's my questions about Linux and the whole installation process and how ...
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Understanding sysinfo Ouput for Custom Init Process

With qemu: qemu-system-x86_64 -s -S -enable-kvm -m 512M -drive format=raw,file=myos.img -kernel {5.11.6-kernel} -append "root=/dev/sda init=/sbin/myint nokaslr" The C code (omitted libc ...
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How can I learn why kswapd has very low page reclaim efficiency?

Problem/context I have a (managed) Postgres 10.16 instance running on Fedora 32 in a systemd-nspawn container. Periodically, I see a big spike in "system" CPU usage in our metrics, ...
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Unable to register kprobe

I'm trying to register a kprobe to retrieve the address of a syscall. But all my attempts seem to return -22 as the error code. The sample code below (incomplete but contains the related functions) ...
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What makes the occurrence of the word “redhat” in the Linux sourcecode fluctuate so much

I was browsing this website: https://www.vidarholen.net/contents/wordcount/#redhat,oracle,google,apple,microsoft What I noticed was that at a few points in times the usage of the word "redhat&...
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Does disk quota affect real time behavior?

I am going to use disk quota within a Linux real time system by adding quota_v2.ko. I had a look to the doc of disk quota and did some research, but I cannot find any information about real time and ...
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Not seeing control channel and data interface associated with qmi_wwan evwn though the driver is loaded

I am trying to set up a QMI data and control channel on my Linux host, but been having trouble understanding a few things. When I run lsmod, I see the following $lsmod Module Size ...
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Process states in OS theory vs in Linux

I'm trying to map Linux process state codes (as in ps) to states in the OS state diagram but I can't seem to map them. Is it because Linux process states don't necessarily match the theoretical OS ...
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Why TCP fast retransmit do not work with 3 duplicate packet?

There is a lot of ack '3762420' appears in log of tcpdump. But the retransmit of seq 3762420:3763880 appears so late. Actually, the earliest ack happened at 23:30:13.267439. Why didn't tcp fast ...
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How do_each_thread() kernel macro works?

In Linux kernel to loop over all threads alive you use do_each_thread() and while_each_thread() macros which both defined as : #define do_each_thread(g, t) \ for (g = t = &init_task ; (g = t = ...
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Not able to install realtek rtl8723de driver on debian 10.9

I have recently installed debian 10.9 on my system using a non-free kde image. As expected there was no wifi so I had to configure it. I got this after running lspci , 03:00.0 Network controller: ...
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IdeaPad 5 15are05 touchpad not working after fix in Pop!_OS

I have a new Ideapad 5 15 with Pop!_OS 20.04 installed. After the installation, my touchpad wasn't working but I was able to fix that issue using the solution of @theunreal89 given here https://...
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Linux installation not able to find the first partition of the disk during the boot up

I have an hard disk image of an openSUSE installation from a x86-64 machine which I no longer have access to. I'm trying to boot from this raw disk using quemu. If I start the virtual machine with for ...
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What to interpret from dd command in terms of performance?

I am trying to compare the performance of various kernel running in power pc. Here is one of my test. dd if=/dev/zero of=/dev/null bs=1024 count=1000000 I see that in one of the kernel version it ...
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How does linux know to mount / without /etc/fstab

When /etc/fstab gets deleted/name is changed booting into the machine still works, in addition the root file system (/) is still mounted and on the correct storage device, how does it know to mount / ...
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MQ I/O schedulers, but I can't find multi-queue in the code

I have been looking at the mq-deadline source codes. Theoretically, mq-deadline utilizes a per-core sw queue. However, when I looked at the code, I can't find the multiple queues. They do have a per-...
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Why do distros(e.g. Arch) use BOTH initramfs and root={smth}?

I thought the goal of initramfs is to boot a root partition and chroot into it. But I can't understand why do distro developers use initramfs if there is ALWAYS a root={smth} flag.
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How do I determine a device mentioned in “ld: final link failed: No space left on device” message during 'make'

I am trying to comlete make command when installing kernel 4.19.188-amd64. But I get No space left on device after 2 hours after make command. I increased /tmp folder, set TMPDIR to a folder in home ...
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Why I don't see any increase in “Dirty” memory when writing to a file?

I read a bunch of stuff about "Write-back" mechanism today and wanted to try an experiment. EDIT: file downloaded from the Internet shows up in Dirty stats Based on the comments, I tried to ...
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What does btusb.enable_autosuspend=n really do?

Bluetooth is a mess in linux. After hours of trying to make bluetooth even turn on, I found out that adding this to the grub fixed the issue to where now it's at least turning on albeit not pairing ...
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35 views

Remove kernel module in use

I would like to remove some kernel module (bluetooth) without rebooting my device. When I'm trying to remove it, a fatal error appears. # modprobe -rf btbcm modprobe: FATAL: Module btbcm is in use. I ...
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Can Linux Kernel CONFIG_RETPOLINE be dropped on for Enhanced IBRS systems?

I'm working on a deployment of systems that exclusively use Cascade Lake processors, which support Enhanced IBRS for Spectre v2 mitigation. I see that in kernel source, if I set spectre_v2=auto on ...
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ext4_mb_generate_buddy Filesystem Error

I'm facing the below filesystem error in SSD type disk with software raid configured machine. Is there any possible cause for this issue? Thank you for your help in advance. Kernel Version: 3.10.0-957....
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Set interface-name to net0 instead of ens18 during unattended installation

I am struggling with a problem I can not solve at the moment. Using PXE-boot to run an automated installation of Debian 10, the installer is setting the interface's name to ens18, which follows https:/...
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How to install kernel-headers/devel-4.x on CentOS7

I cannot figure out how to install kernel-headers/devel-4.x on CentOS7. I want to compile a program using headers from a later kernel version without having to upgrade CentOS. I'm running CentOS 7.9 (...
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Linux kernel with ZFS eating my ram (2x of arc_max)

First up, It seems my kernel is using way too much ram $ grep Slab /proc/meminfo Slab: 21794184 kB See all of /proc/meminfo and /proc/slabinfo $ free -h total used ...
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How to compile Linux Kernel 0.95 and run it with QEMU?

I want to compile Linux Kernel 0.95 and run it with QEMU. But I just found this (Linux Kernel 0.95 source code).
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Function Level Reset notification to Linux PCIe device driver

This query is regarding Function level reset feature for SRIOV. As per code in Linux PCIe driver the function level reset is done by writing 1 to reset under sysfs interface: echo 1 > /sys/bus/pci/...
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38 views

How can I install a non real-time kernel in my Debian box?

I setup a box with Debian: # cat /etc/debian_version 9.13 # uname -a Linux orange 4.9.0-15-amd64 #1 SMP Debian 4.9.258-1 (2021-03-08) x86_64 GNU/Linux And now, I am trying to install CUDA but I am ...
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Hardware clock and date not aligned

On a Linux device I am using the hwclock command and the date command return different values: root@myhost:/home/user# hwclock 2021-04-08 15:12:55.878171+02:00 root@myhost:/home/user# date Thu 8 Apr ...
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145 views

I am trying to install the drivers and the kernel gives me this error:

I am trying to install the drivers and the kernel gives me this error: Kernel preparation unnecessary for this kernel. Skipping... Building module: cleaning build area... make -j1 KERNELRELEASE=5....
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Reading TTY does not work with cat

I have a /dev/ttyUSB6 device (modem) which I was able writing to and reading from like so: stty -F /dev/ttyUSB6 speed 9600 line 0 -brkint -imaxbel -echo echo "ATI" > /dev/ttyUSB6 cat /dev/...
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Kernel panic - not syncing: unable to mount root fs on unknown-block(0,0) after building a kernel without initramfs

While trying to install KISS Linux (a distribution which doesn't use (or at least doesn't by default) an initramfs), a distribution that requires you to build your own kernel, I always get the same ...
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Set quotas for disk usage to a system

I have a remote server. Every time, after a short while, I have a problem with free space, my disk usage (/dev/sda) becomes 100%. This is real problem because I can't easily free space. Most options (...
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How much percentage should zram take?

I'm setting up zram on my server, let's say I have 4GB ram, should zram take 3.5G or 1G or something in between? What trade off will I have when going to the extremes? And, for example I have a single ...
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35 views

Why is `kprobes_register` (kprobes) able to retrieve symbol addresses for symbols like `flush_tlb_all`, but not `sys_call_table`?

Consider the following kernel module source, which uses kprobes_register to get the address of a kernel symbol. It works for symbols like flush_tlb_all, but not for sys_call_table. A quick lookup ...
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Why doesn't the symbol address reported by `register_kprobe` (kprobes) match the symbol address in /proc/kallsyms?

I want to look the address of Linux kernel symbols up using kprobes_register (kprobes). After having planted kprobe for flush_tlb_all, I look up the address using sudo dmesg: [1055.285848] Planted ...
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Adding an if condition inside the grub configuration file

By default when I have only one kernel, the output of ls /boot/ | wc -l is 13. However, sometimes I want to compile and install another kernel to my system and after that I want the grub menu to pop ...
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How can my PCI device driver remap PCI memory to userspace?

I am trying to implement a PCI device driver for a virtual PCI device on QEMU. The device defines a BAR region as RAM, and the driver can do ioremap() this region and access it without any issues. The ...
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38 views

Is rebooting necessary after oom-killer kills a user process?

Is rebooting necessary after oom-killer is invoked on a user process (not a system critical process)? Is there any chance of anything being in a bad state other than the user process that was killed. ...
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1answer
87 views

What's the point of naming Iptables' tables as “tables”?

After reading some guides (e.g. this one) and playing with Iptables tuning I found that I see no reason for naming Iptables' tables as tables. I mean that there practically are no tables. E.g. having &...
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29 views

Custom Kernel module not being loaded

I've modified a kernel module (qcaspi) and recompiled it, however my modifications aren't being called (checked dmesg) when the OS boots up. Instead, the old kernel module is being run. If I reload ...
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Accessing calling userland data from kernel

How do I access the registers of the calling userland process from kernel space? For example, if I want to access the stack pointer or r8 or something? If I had a stack pointer to the user stack, how ...
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“No space left on device” with cgroups v2 writing empty string to `cpuset.cpus`

I'm using Linux 5.11 in the unified cgroups v2 configuration. Following cgroups-v2.rst, I'm trying to reset cpuset assignment of a non-root cgroup (to make it inherit the parent's cpuset). According ...

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