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

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Desktop completely freezing on I/O operations

In my old system, I was already having desktop freezes on some heavy I/O operations like apt-get dist-upgrade and copying 4 GB video files. But now, it has become a lot worse: any apt-get install is ...
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1answer
95 views

Unable to boot a kvm guest via qemu/kvm-tools

I am using ARM Foundation Model to emulate a arm-v8 environment(I need both TrustZone and KVM), and I run a kvm-enabled linux on it as the Host OS, the kernel version is 3.14.0(I clone it following ...
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1answer
32 views

How do I know which File Systems my linux supports? [duplicate]

I am working with linux 3.19.0+ and I want to know if my linux kernel supports f2fs (Flash-Friendly File System). How do I know that?
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34 views

How to switch static drivers like switching kernel module drivers?

I have a linux embedded device that I need to switch between USB file storage gadget driver and USB Ethernet gadget driver at runtime. The approach I use now is to build both drivers into kernel ...
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14 views

What is the role of these RPM packages( kernel-debuginfo and kernel-debuginfo-common RPMs, and the kernel-devel RPM)?

I want to know what the role of these RPM packages( kernel-debuginfo and kernel-debuginfo-common RPMs, and the kernel-devel RPM)?
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1answer
266 views

How to explain strange kernel messages?

I have a server running on Debian Wheezy 3.2.68-1+deb7u1 x86_64. Lately strange records in /var/log/messages appeared. First messages of this log starts just after server reboot. 6.222.18 LEN=44 TOS=...
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1answer
11k views

Centos 7.1 still using outdate kernel 3.10 how to upgrade to kernel 4.0

I'd like to upgrade my Centos 7.1 kernel from 3.10 to 4.0 i did successfully in Ubuntu 15.04 using Linux 4.0.1-040001-generic even though i updated it manually it's works fine so please could ...
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1answer
72 views

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 /var/log/...
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2answers
50 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 (i.e....
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67 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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2answers
146 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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45 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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1answer
104 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? I'...
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0answers
105 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 C/...
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229 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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87 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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205 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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2answers
84 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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50 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 3.0;...
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108 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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46 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
36 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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71 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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1answer
17 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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61 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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61 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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54 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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1answer
41 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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3answers
65 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
16k views

How to get back from “testing” to “stable” - Kernel downgrade

currently I am having lot's of fun with apt-get - and the bad thing is, it was my own fault. I had enabled the testing packages in /etc/apt/sources.list to install a certain package. And I told my ...
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2answers
107 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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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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24 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 #grub2-...
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1answer
59 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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83 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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149 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
58 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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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
63 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
45 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
3k 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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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
81 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
105 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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74 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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68 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 ...