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

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Linux + how to know why Linux machine is hung from the messages on the console

As the picture below , my VM Linux machine was hung and I cant login how to identify the reason for the "hung" according to the messages on the console? I also searched more info from the ...
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2answers
47 views

Efficient way to deploy a custom kernel onto multiple hosts

I recently had to do a custom build of the Linux kernel from its source. That custom kernel is now installed on the machine I used to build it and works fine. Now there are other similar systems ...
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32 views

How to interpret some kernel OOPS output?

I'm trying to analyze some kernel OOPS message. I'm able to understand most of the output, but there's still some lines that I have no idea how the should be interpreted. The first thing is PGD which ...
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0answers
84 views

CentOS 7 unable to cleanly umount a bind mount using rbind and rslave

The following sequence of commands will fail on CentOS 7 (kernel version: 3.10.0-327.10.1.el7.x86_64): [hidden]$ mkdir -p A B/a C/b [hidden]$ sudo mount --bind A B/a [hidden]$ sudo mount --rbind B ...
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1answer
176 views

Find Linux kernel build date/time?

In a Linux distro, let's say Ubuntu 14.04, how can one find the time and date when this particular Linux Kernel was compiled/built?
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51 views

module not loaded at boot

I'm on an archlinux 4.4.1-2 and I'm trying to set up a netctl service. Problem is that for netctl to work I need to have bcma and b43 loaded. Since these two are not out-of-tree modules I thought I ...
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1answer
79 views

why process running in kernel mode cannot be preempted [duplicate]

I read that user mode process are preemptive but why not kernel mode process?
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2answers
148 views

Differences between system processes, and user processes, kernel control paths and kernel thread

My understanding is that a process always runs in user mode and uses user space only, and a kernel always runs in kernel mode and uses kernel space only. But I feel that I might not be correct, ...
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38 views

How does vfs_write decide to aio_write of which file system?

We know that sys_write call vfs_write that ultimately call fs->f_ops->aio_write.But how does kernel know which filesystem's aio_write call back function to call?? Moreover I have noticed that ...
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1answer
72 views

Why are Linux versions so confusing?

I was browsing through kernel.org pages and reading changelogs from several different Linux kernel versions. I noticed the version number pattern is extremely awkward: From Linux 2.6.x came Linux ...
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2answers
72 views

How to find out the reason why ssh processes are hanging?

When I run command like iostat -dkx 2 2 via ssh, I get the expected result, but the processes on the local computer are saying alive in status "interruptible sleep". Why is this happening? Is there a ...
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0answers
87 views

How to Modify Android Boot Sequence in Order to Boot From an SD Card

I've been looking into how to boot Android form an SD card, and I came across this thread on XDA, but I am too much of a noob to understand it, and user has stated that she doesn't have the time to ...
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42 views

Mysterious 8 second delay in boot after grub

I have installed Fedora 23 (KDE spin) on an HP Prodesk mini 600 G2. There is one problem I can't quite figure out, though: after grub comes up, and I press enter on any kernel to boot, the screen goes ...
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1answer
35 views

Linux setup compatibility

I want to setup a Linux environment, but I want the system to be bootable in two or more computer systems with different sets of hardware. Can Linux provide that level of hardware abstraction given ...
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0answers
51 views

bcache not working as expected with ramdisk as cache device

I was trying out bcache but i don't have an SSD so wanted to use free memory as a substitute. As ramdisk is listed in /proc/devices as block device i assumed this would work OK but with below simple ...
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1answer
16 views

Abrupt Loss of Brightness Control

So I've had an openSUSE 13.2 (kernel 3.16.7-29) installation running on an Acer Aspire S7-392 for well over a year and have no problems until Sunday. I can't recall if I did an update or what, but I ...
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0answers
45 views

What's different between logical block and physical block?

I know the logical block is viewed by kernel, and physical block is viewed by disk controller. Then, Where the file system like ext3's block is related? Is this logical or physical? I think file ...
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0answers
56 views

How to detect rootkit linux kernel module based?

I found this small rootkit source code implemented as a Linux kernel module. https://github.com/mfontanini/Programs-Scripts/tree/master/rootkit Basically, as you can see, it changes the ...
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1answer
37 views

How to capture my screen video stream?

I try to capture the output of my gpu, the video flux of my desktop, to stream it on another computer. I'm working on a project like a remote control terminal so I can't have any latency. I have ...
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2answers
99 views

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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1answer
41 views

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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0answers
90 views

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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2answers
119 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
82 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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67 views

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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19 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
47 views

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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69 views

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
126 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
52 views

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
50 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
44 views

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
74 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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0answers
60 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
57 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
49 views

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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0answers
39 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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2answers
446 views

Kdump.service FAILED centOS 7

I'm having CentOS 7 64 installed on my desktop. After recent system update, I am getting below error while booting the CentOS 7. Some time system is able to boot and I can work on it. but it gives ...
224
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4answers
20k views

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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0answers
29 views

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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3answers
1k 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
49 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 ...
3
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1answer
119 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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1answer
28 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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104 views

Is there a general USB 3.0 support in OpenWrt?

the only information i found about this topic is outdated since 2011/02: it says there is no support for devices with usb 3.0 "so far"! according to the german wikipedia since version 2.6.30 the ...
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0answers
157 views

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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11 views

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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1answer
45 views

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 ...
2
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1answer
59 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 ...