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

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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 ...
3
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1answer
1k views

Scaling issues of i7 3520M with intel_pstate module on Kernel 3.10.0

Few days ago I updated my openSUSE 12.3 system from Kernel 3.9.8-1.gf3348a8-desktop to 3.10.0-1.g3dcd746-desktop and since then, turbo mode of my i7 3520M is enabled by default and it does not ...
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1answer
3k views

Setting up HDMI output from Linux console

I am currently running Debian Wheezy on a HP Microserver N54L with an AMD Radeon 5450 video card. I would like to be able to play audio from the console through the HDMI port of my video card and ...
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2answers
24k views

What is difference between User space and Kernel space?

Is Kernel space used when Kernel is executing on the behalf of the user program i.e. System Call? Or is it the address space for all the Kernel threads (for example scheduler)? If it is the first ...
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1answer
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How can I mount filesystems with > 4KB block sizes?

I have a 3TB hard disk pulled out of a WD Mybook Live NAS. The partition table is as follows: Model: ATA WDC WD30EZRS-11J (scsi) Disk /dev/sdb: 3001GB Sector size (logical/physical): 512B/4096B ...
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0answers
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built-in command prompt without a shell? [closed]

This is regarding any similarities to the linux/unix kernel with older and simpler operating systems such as MSDOS and Apple DOS 3.3, which had commands built into them and an internal shell always ...
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1answer
801 views

U-Boot Bootup error

I'm running a Debian Linux on a Cubietruck, running off a SD card. When I power on, I get the following error: ## Booting kernel from Legacy Image at 46000000 ... ...
2
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1answer
450 views

how do I safely delete old kernel versions in CentOS 7?

I might be encountering odd symptoms resulting from competing kernels in CentOS 7. So how do I safely delete the old kernels? And how do I know which kernel is the newest one? Below is the ...
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1answer
30 views

How to enable auto upgrade of kernel-devel package when kernel version is upgraded?

I have a USB wireless adapter for which I need to re-install a kernel module every time the kernel gets upgraded to a new version. But for installing this kernel module again, I need to download and ...
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1answer
888 views

psmouse sync issues!

I have Compaq CQ61-420US (64-bit AMD) laptop with Synaptics touchpad checked using $ egrep -i 'synap' /proc/bus/input/devices N: Name="SynPS/2 Synaptics TouchPad" But recently after Arch Linux ...
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2answers
34 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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3answers
951 views

Location of the kernel binary (when not in /boot)?

I failed to find the kernel binary in the standard location in /boot. I've also searched the whole file system for vmlinux or bzimage find / -iname vmlin* find / -iname bzimage However, this is an ...
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3answers
80 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 ...
213
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4answers
18k 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 ...
1
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1answer
44 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 ...
1
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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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0answers
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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2answers
266 views

Linux Kernel - Wacom Tablet (CTL-490DW-S) - Lockout

I'm a bit of a beginner with Linux and after trying to fix this over the last few days I've finally given up and need your help. I'm trying to use my new Wacom (CTL-490DW-S (Intuos DRAW)) drawing ...
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1answer
15 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
21 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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1answer
731 views

How to manually compile Fedora 20 kernel

I am trying to recreate an environment for debugging purposes. I require Fedora 20 specific kernel version (in this case its 3.17.7-200.fc20.x86_64). I have manually compiled vanilla kernel (3.17.7) ...
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3answers
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
23 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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0answers
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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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2answers
1k views

Benefiting of sched_autogroup_enabled on the desktop

I am running a 2.6.37 kernel with sched_autogroup_enabled set to 1. I am not certain that I am seeing the benefits of this patch since: I am launching my applications from the desktop; applications ...
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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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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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3answers
26k views

How to disable USB autosuspend on kernel 3.7.10 or above?

I've updated my HTPC from kernel 3.7.10 to 3.10.7 and it seems CONFIG_USB_SUSPEND is now gone from the kernel options and included in PM. The main problem I'm facing is that I have an external HDD ...
3
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1answer
82 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
2k views

kernel: “echo 0 > /proc/sys/kernel/hung_task_timeout_secs”

I got this errors in syslog. Any idea what does it mean? The system is running on Ubuntu 12.04, kernel: 3.8.0-35-generic #52~precise1 It looks to me like failure when trying to write to disk... ...
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2answers
592 views

[FreeBSD] rc.conf, loader.conf vs static kernel linking

I'm curious: What, exactly are the benefits to statically linking modules into the kernel rather than loading through rc.conf, etc? For example: To add linux emulation, I could add ...
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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
17 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 ...
0
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1answer
785 views

custom kernel and firmware loading

After I have compiled my kernel, and when I type make modules_install, not only are the modules copied into /lib/modules/ but also firmware is copied into /lib/firmware/. The following is the end of ...
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0answers
25 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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0answers
8 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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3answers
11k views

How does the Linux kernel handle shared IRQs?

According to what I've read so far, "when the kernel receives an interrupt, all the registered handlers are invoked." I understand that the registered handlers for each IRQ can be viewed via ...
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1answer
76 views

cannot read key “net.ipv6.conf.all.stable_secret” in sysctl?

I am running kernel version as followings on an Arch Linux computer: [root@router ~ ]$ uname -a Linux router 4.2.5-1-ARCH #1 SMP PREEMPT Tue Oct 27 08:13:28 CET 2015 and I noticed that every time ...
25
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4answers
29k views

How to cause kernel panic with a single command?

Is it possible to cause a kernel panic with a single command line? What would be the most straightforward such command for a sudoing user and what would it be for a regular user, if any? Scenarios ...
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4answers
3k views

running kernel on QEMU

I face this message: Failed to execute /initKernel panic - not syncing: no init found. Try passing init=option to kernel. I am using this command line: qemu-system-x86_64 -hda disk.img -kernel ...
2
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2answers
671 views

Wireless constantly reconnecting on Ideapad running Arch

I just bought a new laptop, a Lenovo IdeaPad U330 touch, and after some struggle (with the Secure Boot stupidity) I have managed to install Arch Linux. I have configured my system, installed all the ...
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1answer
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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 ...
2
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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 ...
0
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0answers
29 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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1answer
5k views

bnx2: Can't load firmware file “bnx2/bnx2-mips-09-6.2.1b.fw”

I just compiled the kernel 3.10.19 from kernel.org. Support for bnx2 is enabled. On my server when I try to start the eth0 interface I got the following error : bnx2: Can't load firmware file ...
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23 views

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
10k views

Buffer size for capturing packets in kernel space?

Going through the man page of tcpdump, it seems kernel can drop the packets if the buffer is full. I was wondering if: that size is configurable and/or where can I see the size for my distro? From ...
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0answers
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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
66 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 ...
4
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1answer
499 views

What does this dd command do exactly?

I have an embedded device with this SD card: [root@(none) ~]# busybox fdisk -l Disk /dev/mmcblk0: 3965 MB, 3965190144 bytes 4 heads, 16 sectors/track, 121008 cylinders Units = cylinders of 64 * 512 = ...