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

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Why is debug_putstr() not being printed during boot?

I'm asking myself why debug_putstr() in arch/x86/boot/compressed/misc.c is not being printed during x86 boot phase, though it is configured to do so with GRUB_CMDLINE_LINUX_DEFAULT="". On other ...
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211 views

check-config errors on Linux 3.19.0 kernel, configured under Ubuntu 15.04 x86-64

I'm new to configuring Linux kernels, and am receiving the following errors when running config-check: check-config: /tmp/tmp.tnqExc0fHn/CONFIGS/amd64-config.flavour.generic: loading config ...
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123 views

scripts/checkpatch.pl: Warning: consider using a completion

I'm currently writing a kernel driver that involves moving large amounts data from userspace to or from a peripheral, via a ring of bounce buffers. The buffer completion callback ups a semaphore, and ...
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68 views

Best way to approach HID_MAX_USAGES kernel errors?

This is an issue I have for the second time now: basically, an USB based device reports some wrong numbers for "HID_MAX_USAGES", resulting in the kernel giving an error message and the device not ...
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0answers
54 views

What is “state-object” in cgroups

I am gathering some idea about lxc, kernel name spaces and cgroups. While reading man lxc-cgroup, i find : lxc-cgroup gets or sets the value of a state-object (e.g., 'cpuset.cpus') in the ...
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80 views

Stack pointer of the interrupt stack

Linux kernel has separate stacks for user mode and kernel mode process and also some special stacks. One of this special stacks is interrupt stack with the size 16 kilobytes placed in the ...
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1answer
61 views

Linux modules take a lot of space [closed]

I'm using the 4.1.2 mainline kernel. The package with image and all modules has 207 MB of installed size. I built a patched 4.1.6 kernel, taking the config from the current kernel and now the drivers ...
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38 views

Does MySQL processes run in user or kernel modes?

I try to count IOPS and I/O size with SystemTap script and use MySQL to be workload. I found mysqld doesn't call systemcall but mysqld has read/write on VFS. So, do MySQL processes run in user or ...
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195 views

Error while trying to compile/install kernel, 4.1.6 on Ubuntu 15.04

I'm trying kernel compilation in Linux for the first time. I'm using the guide here to learn the basics. I'm able to pull the source code from the git repository, and can compile it. However, I run ...
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32 views

X stopped working after a kernel update

My system is a laptop with Ubuntu 14.04, with an Intel CPU and Intel + Nvidia GPU combo. After one automatic kernel update, the GUI stopped working. It shows a blue loading screen with a spinner, up ...
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11answers
5k views

What's the philosophy behind delaying writing data to disk?

In Linux, a finished execution of a command such as cp or dd doesn't mean that the data has been written to the device. One has to, for example, call sync, or invoke the "Safely Remove" or "Eject" ...
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180 views

how to set i2c bus to soc audio codec

I'm working on an audio codec driver for cs4245 device. It's controlled by i2c. I have 2 hardwares (devel-board), one of the them has the codec attached to i2c-1 and another to i2c-2. The first one is ...
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2k views

How to add a system call in linux kernel 4.x

I'm trying to add a system call using linux kernel 4.1.6 but all the documentation I can find is for older versions. Does anyone know how it's done in the newer kernels or have any good references? ...
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25 views

how practical the number of cores in Android

I've often wondered how practical the cores usage in Android smartphone. I'm asking here because Android is based on Linux. I'm looking from technical perspective. The articles that I've read so far ...
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237 views

Does this bug indicate an error in my btrfs filesystem of simply a bug in the 4.2.0-RC5 kernel?

I'm not sure this is the right place to ask this... I have been running a pre-release kernel (4.2.0-rc5) and yesterday had a possible disk error on my 6-disk raid-1 btrfs filesysystem. While trying ...
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38 views

How do I track down why my system is unstable?

I am experiencing a problem where I use Chrome on my X220 with CentOS 7 (kernel 3.10.0-229.el7.x86_64). It begins when I've been surfing Chrome for a bit and have a few tabs open. Chrome may just ...
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61 views

What module in the kernel that inform the DHCP client to start DHCP negotiation?

DHCP client is a process instead of kernel code. How the DHCP client know when to start sending DHCP discover message? Is it the IP module in the kernel that inform the DHCP client?
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login shell (bash) - how to we invoke a login shell

I know what is a login shell and the difference between a login shell and a non-login shell. But what puzzles me is how it is invoked. It is said that a login shell is invoked with a - as argument ...
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185 views

Status of UVC 1.5 support in Linux

My (Debian 8) kernel, 3.16.7 only detects the Logitech C930E webcam as UVC 1.0 (when it does support 1.5). Searching the Internet only throws up kernel patches, most of them from Pawel Osciak form ...
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148 views

Wifi driver on Kernel 4.x

I've upgrade my kernel from 3.19 to 4.1.5 but the Wifi driver don't work. Does anyone know how I can make it work? I've tried a few methods but it doesn't work. First method I've tried was to try ...
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15 views

How to compile a third party driver in to the kernal? [duplicate]

I am using Linux Mint 17.2 on Toshiba c640. As my LAN driver is no more functional, I am using a USB to LAN converter which was provided with some driver installation files. Every time i want to use ...
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1answer
274 views

How to compile a third party driver into the kernel?

I am using Linux Mint 17.2 on Toshiba c640. As my LAN driver is no more functional, I am using a USB to LAN converter which was provided with some driver installation files. Every time i want to use ...
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1answer
46 views

New Kernel does not automatically reconnect to network

I tried playing around with compiling my own kernel. Everything is fine so far, except for that one thing. Whenever I leave a wifi network or unplug my ethernet cable the system does not recognize, ...
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561 views

iptables - why do I get “Table does not exist (do you need to insmod?)”

I need to install some iptable ruels to block traffic that originates from a certain country, I found this script example on http://www.cyberciti.biz/faq/block-entier-country-using-iptables/ it works ...
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88 views

How does Linux kernel know that collisions occurred in Ethernet collision domain?

Let's say that I have a following network topology: Theoretical total(Tx + Rx) bandwidth for all four hosts in total is 100Mbps. Now if I execute Iperf in UDP mode in all four hosts simultaneously ...
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137 views

Windows Internals for Linux [closed]

I've recently been reading Windows Internals version 6 (from Microsoft Press), and found it thoroughly enjoyable. I'm now using Kubuntu on my work machine, and as such have some desire to learn a bit ...
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71 views

Test program to configure MPLS datapath in Latest Kernel 4.1.3

Latest Kernel supports MPLS datapath in kernel, However there is no test program, or any guide how to write user space program to configure a MPLS datapath in kernel. I browse the kernel code and ...
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364 views

Linux Userspace PCI driver options? (uio_pci_generic)

I have a Xilinx FPGA PCIe end-point on the PCI Bus. Linux picks up the device just fine and everything in lspci looks perfect. My question is about PCI access options from user-space and what would ...
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65 views

Increasing Kernel Mode Setting (KMS) scrollback buffer size

I'm using Kernel Mode Setting to set my server's tty resolution. I added GRUB_GFXMODE=1280x1024x24,auto to /etc/default/grub, and GRUB_GFXPAYLOAD_LINUX=keep was already there. There's no vga= or ...
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444 views

Unable to install new kernel in ubuntu server. “gzip: stdout: No space left on device” error even though abundant disk space

I am trying to install a new kernel on Ubuntu Server and I am unable to complete it due to a "gzip: stdout: no space left on device" error. The full error was produced after running sudo make ...
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2answers
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Understanding the relation between FreeBSD kernel configuration file and actual device

To my understanding, FreeBSD's kernel is configured via text files. Each kernel configuration entry is on a single line. Many entries also have comments set off with a hash mark. The GENERIC conf. ...
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242 views

debian testing hangs on wakeup from s2disk / hibernate

My machine (ThinkPad x230) hangs on wake up from s2disk or s2ram after a recent aptitude safe-upgrade.† The hang looks like a blank screen with a blinking cursor in the upper right after loading data ...
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1answer
50 views

is it possible to run ubuntu kernel on fedora root filesystem?

My concern is theoretical possibility of running ubuntu kernel with fedora root filesystem (e.g. 3.2.58 ubuntu kernel on fedora 22). It's long story why I need this.. Also, I have no chance to make ...
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1k views

Uboot passes arguments to kernel!

How can uboot pass command line argument to kernel? I did some googling and got to know that it uses the bootargs environment variable. There it was mentioned that setenv bootargs key=value. Since I ...
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CONFIG_NF_CONNTRACK is not set

I am trying to setup iptables on udoo quad but I hit a brick wall and cannot find a fix anywhere: root@udoo:/# uname -a Linux udoo 3.0.35 #10 SMP PREEMPT Wed Jul 30 18:16:10 CEST 2014 armv7l ...
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2answers
269 views

How to get the name of USB driver in use in linux

I'm running Ubuntu 14.04 on my laptop. I'm having USB related issues in my laptop. It works sometimes and sometimes doesn't. I thought of fixing the issue myself. So, I wanted to know if there is a ...
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248 views

grub2: error: /vmlinuz-3.16-ucs109-amd64.efi.signed has invalid signature

I am using a derivative of Debian, called Univention Corporate Server. It's a nice appliance that I use for my home server. Yesterday I upgraded to the newest version and since then my server does not ...
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76 views

Option to configure Linux kernel to run userspace script when core dump occurs?

Is there any option in the kernel compilation or userspace setting to do the above? I'm looking to add a crash reported to my new embedded Linux system.
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What could cause dropping cache to be extremely slow on a large cluster?

I'm attempting to time file I/O on my disks. In order to make sure all the I/O is happening off the hard drives and not from ram, before I time any read, I run a drop cache command. Specifically, I ...
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180 views

SLES official repository connection (activation code available for SLES 12, not SLES 11 SP3) solution: use SLES SP4

How could I connected to official repository from my SLES 11 SP3? I need to update my kernel etc. Here my previos active-search post =) How to get 60 day SLES activation code
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2answers
552 views

How to call in a kernel level function in user space [closed]

I've developed some helper functions in the kernel. They're called by other functions in the kernel. Currently, they make my custom kernel panic :( For now (i.e. debugging), I made them as a passive ...
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2answers
369 views

What causes the ata exceptions in my syslog and how to solve them

I have a new system with debian (omv) a SSD hard drive for the OS and a software RAID 6 for the data. I only saw now that I have very regular exceptions in my syslog. I'm worried now, what could ...
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1answer
4k views

What does “kernel:NMI watchdog: BUG: soft lockup” followed by other errors mean?

I have my terminal always opened (Fedora 22), because all my work I do from there. Sometimes I search some info in browser or just have fun. After 20-30 minutes of browsing (browser starts not from ...
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Automatic solution to reduce Linux kernel package size at compile time

Are there automatic solutions to disable unused Linux kernel parts (in particular unused modules) before compilation to fasten compilation? A daemon, that logs used kernel functions (or modules) at ...
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60 views

Signing a module for prebuilt kernel

I am developing linux driver for my own PCI device. I have stucked up on starting my module: [14941.205599] mymod321: module verification failed: signature and/or required key missing - tainting ...
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105 views

Linux: Two different drivers for two (mostly) identical PCI devices

For some obscure reason, I want to use two different drivers for two identical PCI devices on the same system. The drivers have different characteristics, which is why I want one physical device ...
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1answer
153 views

How do I crash Ubuntu Linux 14.04 LTS deliberately?

I'm trying to crash an instance on AWS so that I can simulate what happens when it gets 'stuck'. I tried the top suggestions here How to cause kernel panic with a single command? but unfortunately ...
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1answer
289 views

Does Parallels support 3.18.0-kali3-amd64?

I'm not able to find information on which kernels Parallels supports. I'm trying to figure out if Parallels 10.1 supports this kernel since Parallels Tools will not install no matter what I try. ...
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106 views

Use of MODULE_FIRMWARE(filename) macro in Linux modules

What is the use of the MODULE_FIRMWARE(filename) macro in Linux kernel modules?
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4k views

Empty kernel directory but kernel-headers are installed

Host - Windows 7 Guest - CentOS I am trying to install kernel-headers using yum since during the installation of vmware-tools I get a message asking for the path to the kernel header files for the ...