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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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12 views

journald flooded by kernel messages

My journald log was at some point filled up with kernel messages like this. Mar 12 05:03:53 workstation.mydomain kernel: FAT-fs (sdd1): FAT read failed (blocknr 1785) Each followed by a message ...
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0answers
16 views

Own boot parameter in Linux kernel gives no outprint (Homework)

The task is to write a own boot parameter in the linux kernel that activates printk under the kernel initiation. The Linux kernel version that is edited is 4.16.7 (buildroot 2018.11.2) and my ...
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1answer
18 views

Change CPU count on live Linux VM

Is it possible to change the number of VCPUs on a KVM virtual machine on Linux without stopping it first? The Linux kernel has calls for addition and removal of CPUs (CPU hotplug in the Kernel) for ...
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0answers
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Linux boot-up error : initcall returned with disabled interrupts

We are developing an emulator for RISC-V ISA and during the Linux boot we are getting following errors. It seems do_one_initcall in init/main.c is returned with disabled interrupts. I am getting this ...
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0answers
22 views

Are bind mounts just another mount of the same filesystem?

I'm reading What is a bind mount? I tried mount --bind -o ro / /mnt, then I get the folowing two lines in /proc/self/mountinfo: 23 0 0:21 /ARCHLINUX / rw,relatime shared:1 - btrfs /dev/sda rw,...
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3answers
3k views

Does the Linux kernel need a file system to run?

My opinion is yes, it does, because all useful exposure to the outside world (non-priviledged processor mode) would first require a process running in the outside world. That would require a file ...
3
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1answer
17 views

Permission denied when cd to symlink'd dir in /tmp that is 700 and owned by regular user

Question: Why am I not able to cd into a symlinked directory with 700 permissions, owned by a regular user, as root, when I am able to change into the directory itself? Example: ttucker@plato:/tmp# ...
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1answer
43 views

Root shell in system filesystem with GRUB

I'm learning about GRUB and, after search for a while, I tried to get a root shell changing the kernel load string: /boot/vmlinuz-4.9.0-8amd64 root=UUID=e8485edc.... ro single to /boot/vmlinuz-4.9....
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0answers
17 views

How do I build the mainline kernel with all default Ubuntu modules?

My normal way of building a mainline kernel has been: $ sudo apt build-dep linux $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git $ cd linux $ make localmodconfig $ make -...
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0answers
36 views

Are WiFi, audio, video modules included in the kernel?

I have an old netbook based on WM8880 SoC (https://laptop.fossee.in/) which used to run lubuntu 16.04 (customised heavily by the fossee team) via Uboot bootloader fairly well, one fine day it said I ...
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1answer
40 views

How I can create light Linux version to run only a specific GUI application? [closed]

I have a java application and I want to run this application on light version of Linux server, so all that I need from my Linux is to run the java application. I don't want to run a full desktop ...
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0answers
15 views

ath10k QCA9377 doesn't load wifi unusable [closed]

The wifi load dead slow in ath10k QCA9377 i tried using various other adapter it works fine only on this it is dead slow (not a useable speed) is there is any way to load wifi in a usable speed? *-...
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2answers
51 views

Linux kernel patch

I am reading "Linux kernel module programming" by Peter Jay Salzman, and in that book they say sys_call_table is no longer exported in 2.6.x kernels. If you really want to try this DANGEROUS ...
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0answers
11 views

Hibernation with encrypted home and swap without initramfs

I have a Linux setup with an encrypted /home/<username> (LUKS) and without an initramfs. I currently have an unencrypted swap partition, intended for hibernation. For security reasons, I would ...
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0answers
38 views

How to add a system call to linux version 5.0 kernel? [closed]

I am trying to add a system call to my personal download of the Linux 5.0 kernel. As I understand it, this involves modifying certain files in the Linux kernel, but I can not find which one(s) I need ...
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5answers
290 views

Why is Linux not an operating system? [closed]

I checked the dictionary definition of an operating system: the low-level software that supports a computer's basic functions, such as scheduling tasks and controlling peripherals. Well, that ...
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2answers
30 views

install smcroute in Linux

How do I install smcroute in Ubuntu 16.04? If I try to install using apt-get, I am not finding the commands "smcrouted" and "smcroutectl" in bash. Also, the GitHub page asks to configure the kernel to ...
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2answers
37 views

Best method for searching linux kernel changelog from 4.18.0 to 4.20.16

My question is similar to this question: Where to find the Linux changelog of minor versions But I would like to search all changelogs from 4.18.0 to 4.20.16 for any reference to a specific word, ...
2
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1answer
21 views

How do linux-kernel schedule processes with weight value?

I am reading "Linux Kernel Development" and I don't understand weight value of process. In linux kernel, each process has a nice value, and then mapping nice value to weight. I think weight is "the ...
0
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1answer
42 views

I found kernel code that makes system calls. But I thought that was not allowed?

Context: linux-5.0/Documentation/process/adding-syscalls.rst#do-not-call-system-calls-in-the-kernel Firstly, kernel code cannot call functions like "sys_xyzzy()" anymore, because they have the wrong ...
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1answer
45 views

Implementing ioctl inside the kernel [closed]

I am working on Linux kernel 4.19.2. I want to read performance counters available without using perf or any such tool. From the userspace, I use code as follows. #include <stdlib.h> #include &...
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1answer
24 views

How do you turn on Adiantum on Linux 5.0?

I read recently that Linux 5.0 introduced support for Adiantum, Google's low-power encryption standard, and I felt like playing around with it. But, I can't find anything on the Internet about it, so ...
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0answers
11 views

Where is the default value of write_wakeup_threshold defined?

When reading /proc/sys/kernel/random/write_wakeup_threshold on various Linux systems I get different values. So I assume its default value is not generic but might depend on the Linux distribution, ...
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1answer
29 views

I have just deleted modules.builtin.bin, and now I can not remove any module

I got this error: rmmod: ERROR: ../libkmod/libkmod.c:514 lookup_builtin_file() could not open builtin file '/lib/modules/4.15.0-29-generic/modules.builtin.bin'
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0answers
29 views

Arch Linux freeze: “kernel: watchdog: BUG: soft lockup” and once more w/o logs - how to investigate

I just bought a new desktop PC and had a freeze a week ago. Looking into the kernel log reveals a soft lockup (from journalctl -xa): Mar 03 23:48:55 xxx kernel: watchdog: BUG: soft lockup - CPU#6 ...
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1answer
46 views

How to Disable Kernel module installation capability in Unix Based operating system?

As we are living in the Linux kernel rootkit era, Is there any way to Disable any additional module to load into operating system kernel by any user or any operation or command , in Unix? some sort of ...
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0answers
18 views

Want to know the reason for “Kernel: Page allocation failure: order 0 mode 0x201db”

Our ARM Cortex-A5 processor board used at work has been crashing randomly with following journalctl logs. ourApplication.bin[746]: Error: Custom Transport GET failed ourApplication.bin[746]: : ...
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1answer
19 views

Which format is the correct format to use for mkinitcpio.conf?

I am confused about which is the proper formatting to use within mkinitcpio.conf ... I have noticed sometimes double quotes are used and other times parentheses to close off the users desired hooks, ...
2
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0answers
13 views

How are cpu.cfs_ period_us defined in cgroups and kernel.sched_cfs_bandwidth_slice_us related?

I've been trying to understand how the Completely Fair Scheduler in the Linux kernel does CPU bandwidth control. After many readings, I still cannot understand how the CFS allows for each cgroup to ...
2
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1answer
42 views

Gigabit ethernet requires replug to work for kernel 4.20

I have a Microchip sama5d36 board that has a gigabit ethernet (KSZ9031RNX) and 10/100 ethernet (DP83848J). When I use kernel 4.20 the gigabit ethernet wont connect until I unplug and replug the ...
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0answers
28 views

mmc image does not get initialized with QEMU arm emulator

I'm trying to emulate below i.MX6Q device using QEMU emulator version 3.1.0 on host machines with #41-Ubuntu 4.15.0-38-generic SMP. CPU: Freescale i.MX6Q rev1.2 at 792 MHz Board: Mx6Q 4G Boot ...
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0answers
23 views

“rpm -qa kernel” command lists only older version of the kernel on CentOS. why?

Typing rpm -qa kernel on CentOS terminal only shows kernel version - 3.10.0-957.5.1.el7.x86_64 but I do have 4.20.12-1.el7.elrepo.x86_64 also installed and currently running. $ rpm -qa kernel ...
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1answer
36 views

No system call when malloc after free

While I was playing a little with kernel audit system, I made a small C program: #include <stdio.h> #include <stdlib.h> int main(int argc, char** argv){ void *t; while(1){...
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0answers
34 views

What makes networking packets? [closed]

I'm confused about what parts of a linux system do what when it comes to networking. I'm looking for a good reference about more than just the network layers. Starting with network layers though, ...
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1answer
58 views

Why use tristate vs bool in the Linux kernel Kconfig?

Here is my current understanding of why one would choose to use one vs the other, can you please confirm or correct me? Run-time vs compile-time: If you don't know whether or not you want this ...
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2answers
89 views

Does Linux represent an opened directory in the same way as an opened file?

Linux kernel represents an opened file as an entry in the file descriptor table, an entry in the v-node table, and an entry in the open file table. Does Linux kernel represent an opened directory ...
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1answer
22 views

Can I stop a system call before it is executed using Stackable Filesystems? [closed]

Let's assume that I have an application X. I only track system calls that X issues. For example in systems like "CS-STILo". The system detects anomalous sequences of system calls to detect code reuse ...
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2answers
73 views

Are system calls part of the kernel or are they part of the OS?

When a user issue a system call, an interrupt is fired, which switches execution to kernel mode, and then the interrupt handler responsible for system calls execution is executed. Now I believe that ...
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1answer
10 views

Building modules for a precompiled kernel

Actually I am learning kernel module programming and I have learnt how to build and insert a kernel module but now I want to learn that how to build kernel module for a precompiled kernel.
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2answers
2k views

ip vs ifconfig commands pros and cons

At some point, in some teaching material (from Linux Foundation) on Linux that I came across, the following is mentioned: ip command is more versatile and more efficient than ifconfig because it ...
2
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1answer
25 views

Kconfig: Why ``CONFIG_DRM_TTM`` is not displayed by kernel config tools?

There is an option in drivers/gpu/drm/Kconfig: config DRM_TTM tristate depends on DRM This option adds several functions used by DRM GPU drivers to manage videocard memory, ...
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0answers
31 views

Does it work? Ryzen 1800x and XFX RX590 on 4.15.0-46-generic?

I'm thinking on buying a Ryzen 1800x together with a XFX RX590. I've been doing some reading but couldn't get my mind clear so I thought about asking someone with actual experience on these hardware. ...
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1answer
56 views

Latest kernel update issue

I have updated to the latest Kali Linux 2019.1 Release but my kernel is still stuck on 4.18.0-kali3-amd64 grep VERSION /etc/os-release VERSION="2019.1" VERSION_ID="2019.1" How do I update to the 4....
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0answers
16 views

Performance reduction activating trace-functionality in kernel

Is there any performance reduction to be expected from just activating trace (ftrace) functionality in the Linux kernel, but not using it at run time?
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1answer
129 views

How does the Linux Kernel handle newer chips that patched only against Spectre Variant 1 but not Variant 2?

How will chips patched for Spectre Variant 1 and Meltdown, like Whiskey Lake and Amber Lake, handle Spectre Variant 2? I'm looking to spec out a new laptop. Currently evaluating the Lenovo x390. It's ...
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3answers
76 views

queueing in linux-htb

I am trying to understand the queuing mechanism of linux-htb QDisc and QDisc of linux tc in general. I am new to networking and want to get my basics cleared about how a packet is processed inside ...
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0answers
23 views

Mainline Linux kernels make updates impossible?

Using Ubuntu Kernel Update Utility (UKUU) I installed a mainline Linux kernel (4.16.18). I soon discovered that when starting the Update Manager it requires the new kernel to be uninstalled. The same ...
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1answer
63 views

Writing to /dev/kmsg randomly shows up in /proc/kmsg and always in dmesg?

When writing a message to /dev/kmsg while tailing /proc/kmsg the messages show up very randomly, in never shows up in /var/log/kern.log. However, dmesg gets all the messages correctly. Example # ...
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0answers
26 views

Linux kernel: how to load module last

I wrote a kernel simple module, and I can select my module with make menuconfig. The module compiles and executes without a problem. Is there a method to force the kernel to load my module last - ...
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0answers
28 views

Frequent Kernel Panics, how to solve?

I have a HP Laptop, with the following configuration: Intel i7-5500U CPU @ 2.40 GHz NVidia GeForce 940M Intel HD Graphics 5500 8GB Ram I installed Manjaro i3 on it, and am getting frequent Kernel ...