The kernel of operating systems popularly known as Linux, or sometimes GNU/Linux.

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NMI received for unknown reason 20 — Do you have a strange power saving mode enabled?

I am using Debian GNU/Linux 7.8 (wheezy). While running my MATLAB program today, I got this message in terminal. Message from syslogd@sas21 at Jul 18 16:40:49 ... kernel:[1747708.091929] Uhhuh. NMI ...
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29 views

Is a disabled kernel option equivalent to not loading the corresponding module?

Suppose I set a tristate kernel configuration option to be built as a module, but I don't load the corresponding kernel module at runtime (and it doesn't get loaded automatically). Is the ...
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How to troubleshoot Fedora kernel bug

Bug 1236215, reported to the Redhat bugtracker has not gotten any attention in over 3 weeks. I'm trying to track down the cause myself, but I'm not sure how to proceed. The problem was introduced in ...
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Why does Linux scheduler have locks for run queues?

Why does Linux Kernel Scheduler code have locks for run queues? Does the scheduler spawn kernel threads, and locks are to prevent two of such threads to avoid modifying run queues at the same time?
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25 views

edit module requirements when compiling kernel

I would like to compile the realtime kernel for raspberry pi (https://github.com/emlid/linux-rt-rpi) and want to use the pi with a soundcard - the tascam us122l. The problem that I have is the ...
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28 views

Why am I able to compile kernel modules without “#include”ing the relevant header files?

Based on the common practices shouldn't I have to include <linux/stat.h> and <linux/module_param.h> in the following program? #include<linux/module.h> char str[7] = "hello"; int ...
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28 views

Difference between Current and RC Kernels?

What's the difference between wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.2-rc1-unstable/linux-headers-4.2.0-040200rc1_4.2.0-040200rc1.201507051635_all.deb and wget ...
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44 views

Modify the graphical parts of the Android OS [closed]

I’m going through the Android kernel and Google Glass kernel, and I’m trying to find the graphical parts of the operating system. I want to modify things like the splash screen displayed while the OS ...
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44 views

Why can the waitpid system call only be used with child processes?

The man page wait(2) states that the waitpid system call returns the ECHILD error if the specified process is not a child of the calling process. Why is this? Would waiting on a non-child process ...
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How to confirm CONFIG setting made with make menuconfig?

I poke around make menuconfig select this, deselect that. Rebuild a linux kernel and boot up with it. How can I confirm the selection(s) I made via menuconfig exist after booting? lsmod?
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230 views

Where is the RHEL7 kernel source code installed?

I install the Linux kernel source code RPM: [root@localhost ~]# rpm -ivh kernel-3.10.0-229.el7.src.rpm warning: kernel-3.10.0-229.el7.src.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY ...
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What is difference between different cpu.cfs_period_us values?

I'm reading kernel[1] docs and confused about the cpu.cfs_period_us in this part: 3. Limit a group to 20% of 1 CPU. With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU. # echo ...
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114 views

Where in the kernel /dev/kmsg gets initialized?

I'm trying to figure out at which point in the boot up process /dev/kmsg gets initialized and can thus be written. On my system the first line that occurs in dmesg is printk(KERN_INFO "Initializing ...
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58 views

ACPI – how to select correct LED and LCD module

I'm facing a strange issue. I have ASUS x551ma notebook; As I can get it, after a while (20-30 min) watching LCD, I suffer eye strain. The graphics (video card) seems fine but the LED is micro-shaking ...
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19 views

How to add version number to custom kernel and rootfs?

I have a small embedded project where I had to make some minor tweaks to a linux kernel to support different hardware and minor tweaks to a debian-based operating system (my rootfs). uname -a no ...
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56 views

Custom driver for keyboard GNU/Linux 4.1.0-rc8 (Fedora)

I am writing a driver for a Logitech G110 USB keyboard for Kernel 4.1.0-rc8. My driver is perfectly loadable with insmod (Debugging message prints to dmesg that it get's initialized through ...
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63 views

Kernel panic? After ram increase

We asked our server provider to increase ram (from 4gb to 6gb) on our server. After they increased and restarted server, it started giving these messages: Message from syslogd@www at Jul 1 14:39:04 ...
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78 views

Why does my process take too long to die?

Basically I'm using Linux 2.6.34 on PowerPC (Freescale e500mc). I have a process (a kind of Virtual Machine that was developed in-house) that uses about 2.25 G of mlocked VM. When I kill it, I notice ...
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43 views

How does rootfs.ext3 image file work?

I have a FriendlyARM mini6410 device and I have just hardly make it boot from sdcard. Now my sdcard uses "u-boot for mini" (u-boot.bin), "linux2.6.38 kernel" (zImage) and "rootfs qtopia fs" ...
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21 views

How to catch my bluetooth service events

I have usb bluetooth device which is using btusb 0.6 module (driver). The thing is I am interested to know is: how is the systemctl start bluetooth.service event invoked? I was looking info about ...
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27 views

How to determine if the kernel sources are installed?

I just bought a USB 3.0 Gigabit ethernet adapter. It uses an ASIX ax88179_178a driver. I need to build the driver and the readme says: ...you need the Linux kernel sources installed on the build ...
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95 views

Can a kernel preemption happen in the process context with `TASK_INTERRUPTIBLE` state?

If a process sets itself to the sate of TASK_INTERRUPTIBLE, can it be preempted by other kernel components? If it does, I think this process maybe lost wake-up chance due to failed to check the ...
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Legal status of an embedded Linux case

I wanted to find the source code of embedded Linux that is used in Shenzhen Apexis Electronic Co.,Ltd products. For example in this page: http://apexis.com.cn/productsdetails_244.html You see they ...
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23 views

How To Induce RO To Linux FS

I've read in several places that during I/O error to system log file most linux distributions go to read only mode. Followed by how to recover from it. This is all fine, but I'm looking for a way to ...
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91 views

4G modem on an embedded 2.6.32.9 kernel on a Parrot AR Drone 2.0

I am attempting to compile support for a Huawei E3276 usb LTE modem for an embedded Linux/BusyBox installation on a Parrot AR Drone 2.0, which is based on kernel 2.6.32; however, I am running into ...
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91 views

How to get kernel messages on serial console on a systemd system?

I'm trying to set up an A20-OLinuXino-LIME2 as a headless fileserver with a Debian 8 image from Igor Pečovnik's builds. I would like the system to output its kernel messages to the serial console ...
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52 views

Linux process - messages from kernel [closed]

I have been learning about different IPC mechanisms present in Linux, for communication between user space processes. I want to ask what are various ways in Linux for the kernel to communicate with ...
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80 views

Booting encrypted disk kernel error: Cannot initialize device-mapper

I have Ubuntu 15.04 with a default full disk encryption installed on my chromebook Pixel with linux-samus kernel patch and everything is working fine. I've just tried compiling a newer version of the ...
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86 views

APEI Generic Hardware Error : PCIe error with ATTO SAS HBA

Recently we upgraded a remote server to a new Dell PowerEdge T630 with dual CPUs (so all PCIe slots are active). It had been running for several weeks fine before we added an IBM LTO5 tape drive that ...
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15 views

SystemTap log output to file

I want to log output from my SystemTap script to a file. But when I try to use the -o option like: stap -r $PWD --remote user@hostname -o test.txt -S 1 ./test.stp I can't find the log file. If I ...
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326 views

Changing the TCP RTO value in Linux

I will like to alter the TCP RTO (retransmission timeout) value for a connection, and some reading I have done suggests that I could do this, but I don’t where and how. I have looked at the ...
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35 views

What is the register %gs used for?

All I was able to find out about the %gs register is, that it seems to be a free to use register on >32bit x86 architectures. It seems that a gs_change is executed before any system-call. Can someone ...
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35 views

Case study of virtual memory management

Need help in understanding virtual memory concept. When a process requesting for 2GB mapping onto the virutal memory in Linux environment of 4GB ( 1GB Kernel : 3GB Userspace), when already another ...
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61 views

What is the impact on system performance when kernel debug info is enabled?

In order to debug kernel or use tools like stap (https://en.wikipedia.org/wiki/SystemTap) kernel must be compiled with full debugging information included - namely option CONFIG_DEBUG_INFO has to be ...
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bluetooth - btusb module remove stops bluetooth service

I just faced a strange issue; Every time after suspend the btusb module is kicked out the RAM (for some reason but its OK cause I can reinit it manually) but as a result the bluetooth.service must be ...
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40 views

How does the kernel decides what pages commit to swap?

If RAM usage is higher than the level written in «swapiness», kernel will use SWAP. Ok. But how does the kernel «order» programs? Is it «first come, first served» for RAM? Or biggest programs in ...
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Kernel memory leak detection [closed]

How are memory leaks identified in Kernel. Not sure if Valgrind can be used in this case.
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Linux Angstrom can't start without serial cable plugged

I'm using the Altera Cyclone V Soc dev Kit and Linux Angstrom provides by rocketboards (http://rocketboards.org/foswiki/Documentation/GSRD141) Kernel is : 3.10 LTSI Linux can't start if any serial ...
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67 views

How do I detect that my system has auto-rebooted after a kernel panic?

I'm using Linux in embedded systems, and want to configure the system to automatically reboot after a kernel panic. However, when the system comes back up, it's important for me to detect and log the ...
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Telling Linux kernel *not* to use certain CPUs

I'm trying to run some benchmarks on a multicore machine and I'd like to tell the Linux kernel to simply avoid certain cores unless explicitly told to use them. The idea is that I could set aside a ...
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Why is the Linux kernel called an “image”?

I often hear people refer to the Linux kernel as the Linux kernel image and I can't seem to find an answers on any search engines as to why its called an image. When I think of an image I can only ...
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Trace kernel object calls

We have strace to trace programs, ltrace for dynamic libraries, and others. Is there any equivalent for kernel objects, as in tracing just like strace but for a specific .ko? Thanks
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High %sy cpu usage , server is very slow

On one of the server we are noticing high %sy usage due to which server is very slow. Below is strace count for syscall. What will be the reason for high %sy usage. % time seconds usecs/call ...
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Arch very long boot-time after kernel downgrade

I just downgraded my arch kernel from 4.x to 3.17.x for the sake of being able to use shared folders feature in vmware. Right now, everything is fine and it boots up too. But boot-time has greatly ...
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what does it mean 'fork()' will copy address space of original process

I'm studying 'operation system concepts' on my own and I'm studying the chp3. process part. There is an example where the 'fork()' function is called and depending of the returned pid value like the ...
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Minimum required packages for a LFS/DIY-Linux system?

I am trying to make a super-minimal linux system, as a base for experimentation, and just for the experience. I have built DIY Linux (similar to Linux from Scratch) before, but I was wondering how ...
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how to find which linux kernel commit made its way to exactly which kernel version [duplicate]

We have a problem that started appearing in kernel-uek-3.8.13-68.1.2.el6uek.x86_64. Symptoms and description matches exactly this linux kernel developers description ...
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Is there a way to expose extra settings through sysfs using the IIO framework?

The driver I'm developing has a number of settings I want the user to be able to change that don't really fit into the IIO framework. For example, using the IIO_CHAN_INFO_SAMP_FREQ enum in my read ...
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routing table “220” in Linux kernel 3.2.0-23-generic

I have a Linux machine with kernel 3.2.0-23-generic and it has rule with priority 220 in RPDB which points to routing table named "220": T42:~# ip rule show 0: from all lookup local 220: ...
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159 views

routing cache in latest Linux kernels

As I understand, routing cache was removed since Linux kernel 3.6. In systems with older Linux kernel one could view the content of the routing cache with ip route show cache command and routing ...