Everything about UNIX kernels: development, configuration, compilation, design, etc.

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what means 'processor execution level'?

I'm reading about Unix in a book "The design of UNIX operating system". But, in the text middle of process state (e.g wakeup, interrupt), there is term 'raise processor execution level'. What does ...
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Block device disappears after suspend-resume

After few suspend/resume cycles one of my hdd disappears from the list of devices, here is part of dmesg output that seems to be related to issue: [ 450.005310] sd 5:0:0:0: [sdc] Starting disk [ ...
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Error booting kernel 4.5.0-rc1 on Encrypted HDD

I cloned the Git tree of the mainline Linux Kernel and compiled it(version 4.5.0-rc1). After compiling with default configuration (make defconfig) I installed it. In the grub menu I can select this ...
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C/Unix: How to extract the bits from st_mode? [migrated]

I am a beginner to Unix programming and C and I have two questions regarding the stat struc and its field st_mode: When accessing the st_mode field as below, what type of number is returned ( octal, ...
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1answer
19 views

Module vfat fails to load (I've tried the obvious fixes)

The module vfat doesn't load on boot, and attempts to force the issue with a modprobe vfat produce the error modprobe: ERROR: could not insert 'vfat': Unknown symbol in module, or unknown parameter ...
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1answer
36 views

How does linux load firmeware for built-in driver modules

I've learned that the firmware-subsystem uses udevd to copy a firmware to the created sysfs 'data' entry. But how does this work in case of a built-in driver module where udevd hasn't started yet? ...
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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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Location of interrupt vector table in Linux kernel v4.4 [on hold]

I'm trying to find where the vector table is set inside of the kernel, but I haven't had any luck locating it. I have a feeling it is located under arch and is one of the architecture dependent ...
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9 views

RAPL PMU detected, API unit is 2^-32, 4 fixed counters 655360 ms ovfl timer

I compiled my own kernel (version 4.1.5) using the commands: #emerge --ask sys-kernel/genkernel #genkernel all And then I installed grub2 using these commands: #emerge --ask sys-boot/grub ...
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1answer
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How to dump the dmesg AKA Kernel logs to a single .txt file from the kernel boot?

I am trying to understand the SATA Host-Device Communication and for that I have put a lot of debug messages in the kernel driver code. Now messages are in such a huge amount that I am not able to see ...
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79 views

Newly compiled kernel can't boot to LVM root partition - but the old one does

When booting a new kernel (4.4.1 on Ubuntu 15.10) for my Intel i7 based laptop (MSI GS40 Phantom), I can't seem to far past Grub. Once initramfs kicks in I get an error message saying that it can't ...
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Manually move kernel image to /boot directory

I have compiled my own kernel on Gentoo (following the handbook) and then I have moved the bzImage to /boot/vmlinuz-4.0.5. But when I boot the system I get the Grub2 shell. What am I doing wrong? ...
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1answer
29 views

Linux file system corruption due to improper shutdown (fs ext4)?

I have been managing many Linux servers, It is very easy to play with Linux servers than any other OS. But Sometime I encounter a problem with Linux OS is that, The file system corruption. This ...
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3answers
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kernel configs and dependencies

When a particular kernel config is turned on, e.g. CONFIG_CRYPTO_FIPS=y a bunch of other dependencies (CONFIG_XXX_YYYY) get turned on during compilation. Is there a way to know all the dependencies ...
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1answer
33 views

How do kthreads actually work?

Need to implement DHCP server in kernel space. It's supposed to be a multithreading server, and I think I should use kthreads ( I'll be glade if you know better decision ). However I can't understand ...
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2answers
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Generate raw Ethernet frames with memory preloaded payloads at < 1 ms intervals

I am looking to generate raw Ethernet frames with payload that is preloaded into memory. The Ethernet frames (10-60 full frames) should be generated at 1 ms intervals with no exception. What would ...
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1answer
45 views

How to study the linux kernel source? [closed]

I have finished studying Operating Systems about a year ago, and now I'm interested in linux. So I plan to study Linux from the source code. But when I look at the source code, it is really big in ...
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18 views

Process stuck in kernel code, what is it doing? [closed]

I have a process (db_add) which is stuck is kernel code. This process is the only ressource-intensive process running on the machine. Top reports a 100% (ie it fully uses a single core) CPU usage: ...
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1answer
17 views

Which components of Linux IO subsystem are device-independent and device-dependent?

From Tanenbaum's Modern OS, every operating system has an I/O subsystem for managing its I/O devices. Some of the I/O software is device independent, that is, applies to many or ...
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2answers
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What causes a PCI ID to change

When running lspci on my RHEL 7.2 box I noticed my Ethernet Adapters changed PCI bus IDs. In the example below it changed from "02:00.x" to "03:00.x". What might have caused this? Is there a way ...
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1k views

Is the entire kernel loaded into memory on boot?

I read through this popular IBM doc (I see it referred quite often on the web) explaining the function of the initial RAM disk. I hit a wall in conceptualizing how this works though. In the doc it ...
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24 views

Dereferencing string pointer in ftrace event filter

I'm currently trying to create an ftrace event filter for the event sys_enter_open which is filtering by the filename argument. Looking at the format definition of it I can see there's a filename ...
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Kdump.service FAILED centOS 7

I am getting this error on my centos 7 x86_64 after "yum update". After rebooting the host it went into emergency mode. after entering this: systemctl status kdump.service I get this: ...
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4answers
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How does a Segmentation Fault work under-the-hood?

I can't seem to find any information on this aside from "the CPU's MMU sends a signal" and "the kernel directs it to the offending program, terminating it". I assumed that it probably sends the ...
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ASLR implementation details in Linux Kernel

I was able to easily locate code that ranzomizes "stack --> randomize_stack_top()" and "heap (brk) --> arch_randomize_brk()" in Linux kernel. However, I do not see the code which randomizes the ...
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82 views

get rid of “No Caching mode page found” message during boot

during early boot, I get following error message: [sdb] No Caching mode page found [sdb] Assuming drive cache: write through If I understand correctly, this is actually just a harmless info message ...
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1answer
30 views

How do I include the device tree with my kernel?

The purpose of the device tree is to "explain" the hardware to the kernel. But if the kernel is "customized" for certain hardware, how do I "insert" the device tree into the kernel at build time(so ...
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1answer
84 views

Linux exit function

I am trying to understand linux syscalls mechanism. I am reading a book and it in the book it says that exit function look like that(with gdb): mov $0x0,%ebx mov $0x1,%eax 80 int $0x80 I understand ...
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multithread access to platform device driver [migrated]

I am currently writing a platform device driver for embedded linux on ARM. What I've noticed is that a multithreaded application from user space can only access the driver one thread at a time, and ...
2
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1answer
18 views

Managing Pre-Built Kernel Modules Across Kernel Versions

Please read the full question before attempting to answer, this is a bit oddball of a situation. I support a lot of server hardware test functionality, and essentially end up managing several ...
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how to merge device tree overlays to a single .dtb at build time?

My board boots via U-Boot and AFAIK that bootloader does not support device tree overlays, so I'm probably forced to generate a single, static .dtb will all relevant overlays (and settings??) already ...
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Copy a driver to other kernel?

I have installed RemixOS on my Laptop (sony vaio SVF 1521V1EB) but the Wifi is not working... However I could make it working on Ubuntu, so my question that am I able to copy the module files from the ...
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Q: How to tell the Linux Kernel to ignore MULTIPLE ata devices?

So, there were already questions about ignoring ata devices (like How to tell Linux Kernel > 3.0 to completely ignore a failing disk?) from where I got the info that one has to add something like ...
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1answer
46 views

Why does Linux have a maximum number of sound cards? [closed]

I'm specifically asking about CONFIG_SND_MAX_CARDS in the kernel. From the code using this config, for example in sound/usb/card.c for USB cards, soundcards are stored in plain arrays which are ...
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31 views

dd process real vs. sys time

I have two quad core workstations. One is based on Intel Atom x86_64 architecture (WS1). Another one is based on armv7l architecture (WS2). Both are running 3.10 kernel version. Identical busybox dd ...
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How do I support PTRACE_O_SUSPEND_SECCOMP and PR_SET_MM_MAP?

I'm trying to make Criu work. However, when I run sudo criu check, it gives me this error: prctl: PR_SET_MM_MAP is not supported, which is required for restoring user namespaces Error ...
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1answer
52 views

No space left to free up on rootfs partition to upgrade kernel

I want to upgrade Linux kernel from 3.16 to 4.3. Unfortunately when I run aptitude install linux-image-4.3.0-1-amd64 installation fails due to no space on rootfs partition. 117MB left, 174MB needed. ...
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How can I find the module responsible for interaction with keyboard [duplicate]

I have a laptop and want to be able to turn off keyboard for a while. I use this code: modprobe -r usbhid sleep 10 modprobe usbhid But as my keyboard is not usb, and it only blocks mouse. How can I ...
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1answer
64 views

Can a bootable NetBSD be built on OSX?

I've got OSX 10.9.5 . I want to build NetBSD (or at least it's kernel) on my OSX box. I've tried building the 'config' program but I can't find 'build.sh'. Is this possible and what would be the steps ...
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2answers
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In Debian Jessie, make allnoconfig and make allyesconfig generate the same .config file

In debian jessie, I've installed the linux source with: sudo apt-get install linux-source I obtain a file /usr/src/linux-source-3.16.tar.xz, I copy it under my home directory, change the ownership ...
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Shared IRQs not operating properly

I'm having problems trying to make use of four out of six serial ports on my motherboard. The situation is: I have 6 serial ports available - ttyS0 to ttyS5 - of which 0 is a RS232 port on the edge ...
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1answer
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What is the information present inside a kernel core dump

I am running CentOS 6. The system got a Kernel Panic and rebooted. I have enabled coredump generation, hence it generated a Kernel Core Dump of Size 300MB. What is the information that got ...
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1answer
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FreeBSD: How can I install kernel sources for 10.2-STABLE version?

Lots of articles and posts on internet tell how to install the kernel sources for FreeBSD x-RELEASE versions, but none of them for X-STABLE. For example, my FreeBSD version is 10.2-STABLE. How can ...
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Arch linux kernel upgrade from repositories

About two months ago I build a kernel (4.2.6-ARCH) from source according to this page, this is my current kernel version, the problem comes when I try to upgrade from the repositories, actually I did ...
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1answer
67 views

Loading WiFi driver results in the whole system becoming unstable. How to debug?

I am not a linux kernel expert, but I got this new laptop and it's WiFi(RT3290LE) is not working. I tried solutions from various sources and they are not working. So it is upto me to solve it, and I ...
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CentOS update from 7.1 to 7.2 with 2.6 OpenVZ kernel?

We are using CentOS 7.1: $ cat /etc/redhat-release CentOS Linux release 7.1.1503 (Core) We deferred the 7.2 upgrade. It looks like it did not cause any problems so we are planning an upgrade. The ...
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prevent from writing to a large continuous section of virtual memory [closed]

How can an operating system kernel efficiently prevent a user process from writing to a large continuous section of virtual memory?
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Identifying disk drives during RHEL/CentOS/Fedora Installation

What steps are followed in order to identify a connected disk drive during Linux installation ? I am interested RHEL/CentOS/Fedora procedures. Is it entirely depends on the Kernel package and drivers ...
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4answers
112 views

Kernel panic after Gentoo install — cannot open root device

I have a Debian system on /dev/sda1 (/) and /dev/sda2 (extended, /dev/sda5 is /home, /dev/sda6 is swap). I want to install Gentoo in parallel, so I shrinked sda2 and created /dev/sda3, in which I ...
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Unable to setup TL-WN722N or Unable to install/complete headers

I would like to set up the tl-wn722b WLAN Adapter. I have a Kali Linux version for a Raspberry Pi. I tried to follow this tutorial: ...