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

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Debugging a “brutal” system hang (no longer responds to Alt+SysRq+B)

I've had a series of system hangs where I hoped to get a crash dump to at least get some clues but the normal "magic sysrq" functionality is broken too; not even the immediate reboot key works. The ...
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1answer
33 views

How to query EFI signature

It appears that Grub-EFI will only boot a "signed" Linux kernel. Is there some command that will allow me to query a given kernel image to find out what signatures (if any) are present on it?
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Can I use lldb to remotely debug the Linux kernel?

With GDB, I can remotely debug the Linux kernel. lldb, which promises to completely replace GDB, should be able to remotely debug the Linux kernel too. However, I cannot find any tutorial about this ...
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62 views

What does this dd command do exactly?

I have the 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 * ...
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Ubuntu kernel source code package

Can somebody explain me the difference between the following files: drwxr-xr-x 28 root root 4096 Apr 22 12:04 linux-lts-raring-3.8.0 -rw-r--r-- 1 root root 15209788 Mar 14 03:38 ...
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modpost.h:12:23: fatal error: elfconfig.h: No such file or directory

I am running Ubuntu: #lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 12.04.4 LTS Release: 12.04 Codename: precise Kernel info: 3.8.0-38-generic ...
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FATAL: Module hello.ko not found

I'm using CentOS-6.5 and default kernel is 2.6.32-431.11.2.el6.x86_64. I downloaded 2.6.32 and built that kernel (under /lib/modules/2.6.32). I wrote a module for simple hello world program. This ...
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Block physical console access

I'd like to block physical console access to my linux. I'd like to find, which module is responsible for keyboard input (ps/2, usb, ...) and vga output (only physical), so I can remove them from my ...
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48 views

Do I have to compile the kernel every time, even for a small change?

In my project I configure the kernel (2.6.32) in block/ioctl.c. We all know that kernel compiling and building takes few hours. Even for a small change, I'm compiling from scratch. So is there any way ...
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Passing data from kernel space to user space in FreeBSD [on hold]

I need some information regarding write requests from all applications on FreeBSD. I put a function inside the file system write call ffs_write() which collects the information into an array of ...
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39 views

What does “make install” do in the Makefile that comes with the kernel?

I'm trying to identify what does make install do with the kernel and what does the actual "install" of the kernel once it's been compiled means. The problem is I can't really identify the target ...
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Placement of kernel binary and sources for kernel module building?

I'm trying to setup an environment for kernel module development in Linux. I've built the kernel in the home folder and would like to place the sources and binaries to the correct place so include ...
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90 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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768 views

What is meant by “a system call” if not the implementation in the programing language?

I would like to understand the term "system call". I am familiar that system calls are used to get kernel services from a userspace application. The part i need clarification with is the difference ...
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how get net switch info in soc?

I have a router device. cpu is mtk7620n. mtk7620n have a switch. How can i get information of the switch . swconfig show nothing. i think the switch have no driver. Anybody give me some ...
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29 views

Starting my own application at the startup

I am working on zc702 board having ARM Cortex A 9 processor. I have a binary that I got after cross-compilation for ARM (LED blinking). Now I want that this file should execute as soon as the the ...
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106 views

Are system calls the only way to interact with the Linux kernel from user land?

Are there any other interfaces, e.g. the /proc filesystem?
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How to create a custom Linux distribution? [closed]

Can any one tell me the easiest way to create a system with live cd with installing function. Which can install backtrack all tools?? I need to create a custom boot animation and everything!
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1answer
23 views

What is the difference/relation between kernel name and OS name?

What is the difference/relation between kernel name and OS name? Are they always the same thing? For example, I am puzzled at the outputs: -bash-4.1$ uname -s Linux -bash-4.1$ uname -o GNU/Linux ...
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What is the difference of kernel/distribution's release and version?

I use the following command to see the name, release and version of a kernel. -bash-4.1$ uname -s Linux -bash-4.1$ uname -r 2.6.32-279.el6.x86_64 -bash-4.1$ uname -v #1 SMP Wed Jun 13 18:24:36 EDT ...
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28 views

Why is kernel boot starting too late

Log message from ARM Cortex A9 based board. Running petalinux. [Sat Apr 12 19:33:50.207 2014] [Sat Apr 12 19:33:50.207 2014] [Sat Apr 12 19:33:50.207 2014] U-Boot 2013.07 (Apr 09 2014 - 12:31:52) ...
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Correct location of initramfs.cpio file when compiling kernel

I am following this article and generated an initramfs.cpio file. Now the tutorial mentiones that I have to put this file in build directory: Finally, you have to rebuild the kernel again: # 0. ...
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92 views

Why isn't “REISUB” working on Debian?

I'm using Debian 'Jessie'. Sometimes my computer freezes, and then I can't use Ctrl+Alt+Supr to reboot, Ctrl+Alt+Backspace to kill the X Window System nor Ctrl+Alt+F1 to open a new shell. I've read ...
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Ping IP works, nslookup fails. New Kernel

I am compiling my own 3.14 kernel. I fear I may have left out some important networking feature to get DNS working. I can't resolve domain names. I can ping my DNS server. I can resolve using that ...
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Kernel panic not syncing : Attempted to kill init

OEL 5.9 (Tikanga) 2.6.18-371.6.1.0.1.el5 On boot I get the following errors: ... exec of init (/sbin/init) failed!!!: No such file of directory Kernel panic - not syncing - Attempted to ...
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Enabling IP forwarding at kernel compile time

I am compiling a kernel for a router. I know a way to enable IP forwarding in an existing Linux system. At compile time, CONFIG_IP_FORWARD is said to do the same task. I am configuring version ...
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26 views

How to use a built in driver in the kernel?

I am building the 3.14 kernel for a board that requires the intel e1000e driver. I would like this kernel to have the driver built in so that I can remove loadable module support. I have chosen the ...
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18 views

Where are the files created by “make modules” when building and compiling the Linux kernel?

To build the kernel, I do make menuconfig make make modules For step3, where do the files go? What's the location for modules? Can I change it by using any env variables?
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Kernel optimiziations for ioctl AF_INET operations

Our server solution handles many tunnel operation requests (add/update/delete) using the ioctl interface, and the AF_INET address family socket. Aprox. numbers are 100 operations/minute with over 8k ...
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Newly compiled kernel not booting up (vanilla kernel 3.12.14)

I downloaded, configured and installed kernel downloaded from kernel.org. While booting up this new kernel for the first time, this error screen shows which is pointing towards a missing or wrongly ...
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101 views

Can the 25 years of development of the Linux kernel be qualified or abstracted in layman's terms? [closed]

The Linux kernel is almost 25 years old. If I had to come up with the short version on the development history of the Linux kernel since 1991(its inception date), and in partcular since 1994 (1.0.0) ...
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Can a real-time process exist in the 'expired' queue of linux kernel?

In the Linux kernel 2.4: Real-time processes are given a priority of 0-99 and they co-exist in the ready queue along with the nice processes (who's priority goes between 100 and 139). But real-time ...
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73 views

Why is swap used when a lot of memory is still free? [duplicate]

In the below 2.6.18 Linux Kernel (Red Hat) server, there is a lot of free memory, but I see some swap is used. I always thought of swap as an overflow when memory has been depleted. Why would it ...
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76 views

Does an in-kernel firewall sit between the network access layer and Internet layer?

This question is a follow-up to my previous question. Logic for me to says that an in-kernel firewall sits between the network access layer and the Internet layer, because it needs to have access to ...
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How security programs like firewall, IPS and IDS have access to network data?

It is said that kernel responsible for the transport, internet and network access layers for a network data. Then, the network data is passed on the appropriate process based on port number. How ...
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How to verify that my uImage is good?

I had a zImage file and I used mkimage tool to convert it into a uImage format. When I am booting this file, it is not been found by u-boot: Wrong Image Format for bootm command ERROR: can't get ...
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168 views

How we can avoid rebooting the system after partition change with fdisk?

When modifying the partition table, fdisk usually returns the following error message: WARNING: Re-reading the partition table failed with error 16: Device or resource busy. The kernel still ...
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How does one capture traffic on virtual interfaces?

I would like to capture traffic on Linux virtual interfaces, for debugging purposes. I have been experimenting with veth, tun and dummy interface types; on all three, I am having trouble getting ...
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Why isn't the -rt (RT-Preempt) kernel patch included by default in the mainline kernel?

According to https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO , the RT-Preempt patch converts Linux into a fully preemptible kernel. The magic is done by: Making in-kernel locking-primitives ...
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How to automate configuration of the Linux kernel build

I'm compiling a flavor of the Linux kernel based on the default configuration (for an ODROID system), with some additional features enabled. I want to automate this process so that I don't have to ...
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Process in user mode switch to kernel mode. Then the process will have root privileges?

According to http://www.linfo.org/kernel_mode.html in paragraph 7: When a user process runs a portion of the kernel code via a system call, the process temporarily becomes a kernel process and is ...
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How to correctly set kernel command parameter for sdboot

Thease are the kernel command line parameter Kernel command line (user set) root=/dev/mmcblk0p2 rw rootwait console=ttyPS0,115200 I am trying to run linux from sd card, and the file ...
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150 views

What is the relationship between root and kernel? [closed]

Based on part of the first answer of this questions: read from a file (the kernel must check that the permissions allow you to read from said file, and then the kernel carries out the actual ...
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Result from kernel returned to what process?

When a process requires actions that require kernel mode, it uses a system call. So, how are the results returned to the process?
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What happens when I run the command cat /proc/cpuinfo?

What happens when I write cat /proc/cpuinfo. Is that a named pipe (or something else) to the OS which reads the CPU info on the fly and generate that text each time I call it?
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Is my understanding of kernels correct? [closed]

System: Application OS: Scheduler, VMM, IPC, FS Drivers, dispatchers, VFS The above would be a monolithic kernel. In a monolithic kernel all core OS functions are separate from user space. Functions ...
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Does ksplice work with updates from repos?

If there is a kernel update from an upstream repository (such as debian or centos) does ksplice work with those updates? If not, how does one update the kernel without a reboot and without paying ...
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153 views

usb kernel module does not load on demand but works fine with insmod and modprobe from the shell

I have a USB Linux Kernel module that compiles and builds. Running insmod loads my module and dmseg and tail -f /var/log/debug shows me it works as expected. Running depmod -a then modprobe from the ...
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174 views

High performance routing with high churn ruleset. What approach is most likely to scale to C10K and beyond?

I've been asked to create a high throughput router using PC / server hardware. I'm modestly familiar with pf, iptables, and tc, but I've never had such high churn and so many rules. I hope you can ...
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What defines the maximum size for a command single argument?

I was under the impression that the maximum length of a single argument was not the problem here so much as the total size of the overall argument array plus the size of the environment, which is ...