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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0answers
81 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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4answers
5k views

Given vmlinuz and initrd.gz, how do I find out, where the kernel is going to load / (root) file system from?

I'm trying various ways of Linux installation (from iso, flash, iso on flash, kernel on flash, root FS in iso-file on flash...) and want to understand what's going on. My question is: is it possible, ...
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0answers
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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
35 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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0answers
59 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
99 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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1answer
45 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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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
12k views

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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1answer
1k 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 ... ...
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1answer
49 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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2answers
40 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
1k 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
746 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 ...
221
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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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1answer
69 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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1answer
81 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
53 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
52 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
40 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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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
33 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
28 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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1answer
42 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
109 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
608 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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1answer
27 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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0answers
130 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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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
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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
188 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 ...
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4answers
34k 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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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
56 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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0answers
39 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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0answers
62 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 ...
4
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1answer
89 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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1answer
542 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 = ...
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3answers
3k views

ACPI problem with recent kernels

In recent versions of popular Linux distributions (Ubuntu, Fedora, Mint, Debian) I always have to put acpi=off into the kernel parameter list before I want to boot the computer. This happens to both ...
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1answer
81 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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1answer
1k views

Debugging Linux Kernel with QEMU

I was trying to study the debugging of kernel using QEMU. I tried initially and failed due to the fact that there was no virtual file system. The answers to this post suggests that there should be a ...
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4answers
200 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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1answer
589 views

“rcu_preempt detected stalls on CPUs / tasks” message appears to continue

My board continues to display the message below. The terminal does not have any input. What is it with the following message, which I know? (T, g, c, q ...) What is the cause of this phenomenon? ...
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2answers
71 views

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 ...