Questions tagged [linux-kernel]

Questions about Linux kernel and Linux kernel related topics eg. implementation details such as system calls, kernel customization, etc. For Linux user space topics which do not involve kernel details, [linux] or distribution tag are more suitable.

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How to debug an SDIO configuration problem?

We are trying to get an SDIO-based 802.11 module to work on an SDIO port of the beaglebone. We adapted the device-tree overlay provided by manufacturer to our hardware, compiled the driver, the driver ...
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centos 6.10 kernel update ok, grub updated but new kernel isn't loaded

Today on an internal, legacy centos 6.10 server I run yum update It downloaded and installed, without errors, these packages: kernel-headers-2.6.32-754.15.3.el6.x86_64 Tue 25 Jun 2019 09:46:...
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What are the “outstanding problems” (stalls), which might be mitigated by limiting per-BDI writeback cache to N seconds based on observed throughput?

I would like to understand this email by Mel Gorman: https://lore.kernel.org/lkml/20131030120152.GM2400@suse.de/ There are still problems though. If all dirty pages were backed by a slow device ...
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INFO: task reboot:xxx blocked for more than 120 seconds

One of the machine, on reboot, intermittently shows above error. Frequency is quite less, but when it occurs it gets stuck there until it's manually powered down and back-up. INFO: task reboot:4476 ...
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USB keyboard not working after building the mainline Linux kernel on a generic Allwinner A23 Chinese tablet

For quite a while I've been trying to install a Debian distribution on my useless cheap tablet PC. After reading the details of building Linux kernel on ARM architecture Manual Build Howto I've found ...
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How to build iptables kernel module for Yocto?

So I have been having a rough time building the kernel modules for iptables with bitbake. I got the userspace application working, but the net folder is completely missing from my /lib/modules/`uname -...
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42 views

How a file system recognized by an OS? What is the role of an OS in file-systems? [closed]

I want to understand the medium between a file system & an operating system. Does the operating system take care of any file manipulations?
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1answer
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My low and high watermarks seem higher than predicted by Documentation/sysctl/vm.txt

Motivation I wrote an answer here: How large are the "watermark" memory reservations on my system? The "min" watermark for the "Normal" zone appeared as 31449 pages. This is 125796 ...
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Compiling Linux kernel with all available drivers

I'm compiling the kernel for usage in portable USB stick. Which means it must run on any hardware, not just hardware of the machine where it is being compiled. What should I choose in kernel config ...
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1answer
19 views

Information on values in /proc/pid/task/tid/sched

can someone help me out with the meanings of the following terms in the output of /proc/pid/task/tid/sched? avg_per_cpu se.avg.util.sum se.avg.load.sum ravg.demand Do any of these values point to ...
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1answer
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Why is my min_free_kbytes larger than the documented calculation (and larger than the documented maximum)?

My machine has roughly 8GB of RAM. Why is min_free_kbytes set to 67584? The kernel code comment says I should expect to see min_free_kbytes set to around 11584. It also says the largest it would ...
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Does Linux kernel 5.0.9 have a memory leak?

likely similar to Linux memory usage higher than sum of processes except that I have observed used memory going both below and above the sum of process RSS by GBs. uname -sr Linux 5.0.9-... cat /...
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Upgrading Kernel - Subgraph OS Alpha

I m using my subgraph os on laptop downloaded today itself. So I discovered it was running on kernel v4.9, Last OS i was using 4.19 kernel and touchpad two tap scroll and other keys like brightness ...
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1answer
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Find out timer resolution on old and new Linux systems

How can I find the resolution of system timers on Linux/POSIX systems? In particular I'm interested in the smallest time nanosleep() can wait. My existing implementation calls sysconf(_SC_CLK_TCK) ...
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How to fix MPU9250 configuration issue in device tree?

I have set up an i2c protocol which detects the mpu9250 at address 0x68. Now I want to configure the mpu and I have updated my dts file with the following lines of code: mpu9250@68 { compatible = ...
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“Required key not available” error when trying to load signed module

I made a module and compiled it with make modules_install. I ran these commands following this gist: openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -subj "...
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Linux kernel cross-compile failure at arch/arm64/crypto

I encountered an error while trying to cross-compile Linux kernel v.5.0.0 on Ubuntu 18.04. I tested two different versions of aarch64-linux-gnu-gcc: v7.4.0 and v5.5.0, but both results in the same ...
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Automatic module signing for distribution in Linux

I'm new to writing Linux modules (drivers) and digital signatures, so please correct me if any of my understanding is incorrect. When I run make modules_install on my module, I get the following ...
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1answer
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Can user space memory make the system go haywire?

So I was reading How Linux Works by Brian Ward. In it, he says, the user-space applications going bad will not wreck the system. Figure 1-1. General Linux system organization There is a critical ...
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What does this entry in an strace mean?

I already asked the question on reddit, but it unfortunately received no responses. I have the following shell output: [OP@~]$ strace okular file.pdf /* snipped */ write(13, "\1\0\0\0\0\0\0\0", 8) ...
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1answer
20 views

How long does conntrack remember a connection?

From this link it seems that conntrack remembers a connection for X seconds after it is closed. Does anybody know how long that X is and if it is configurable?
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How to access data written in a socket without reading it [migrated]

I'm working on an embedded system having Linux. A client thread is writing some data in the socket but what server thread is reading on the other side isn't the same as it was written. Which is ...
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1answer
53 views

ACPI error message AE_NOT_FOUND. Why is this happening now? It did not happen previously

I have used Linux on my PC for a long time. Some time recently, there is a new kernel error message on the text console. It also appears as a message in red in journalctl -p err. It did not appear ...
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How do I check if my VM is using vhost-net driver for networking

In KVM, NIC model can be set to virtio (latest) or the older e1000 (not recommended, emulated). In virtio, one has the option of using vhost-net driver or qemu. vhost-net and qemu differs in how ...
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2answers
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Setting up a PC to run the examples in “Linux Device Drivers” book [closed]

I am a programmer looking to gain expert experience into the workings of the Linux operating system. I have gone through many tutorials and materials on the basic workings of operating systems and ...
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1answer
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Should the Linux kernel perform an “IGMP rejoin” on link up?

This question is almost the same as an older unanswered question found here in the kernel's mailing list (credits to Simon Paillard). Here's a (paraphrased) recap: When a host running the Linux ...
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1answer
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Does the kernel itself depend on the standard C libraries

I'm looking deeper into how Linux actually works, especially on embedded devices, with all the different components required to make a fully functional system. I understand that a standard C library ...
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18 views

USB device not being recognized by kernel

I'm attempting to connect a programmable vaping USB device to my Linux Mint laptop. Each time I connect the device to laptop, I do not see the device appearing while monitoring lsusb via watch ...
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49 views

How to prevent to install newer kernel when removing one?

On Ubuntu, I've got some trouble with one new kernel (4.18.0-20) so I rebooted on one older one (4.18.0-15). Now I want to uninstall the new kernel to prevent any confusion, but doing this, apt to ...
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How does linux decide the load address and entry point when execve an ELF?

When linux execve() an ELF, it will mmap that ELF into the process's memory space and start to run code from the entry point. But how does the kernel decide the load address and entry point of the ELF?...
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Automate driver loading question [closed]

I want to automate driver loading through hotplugging on an embedded linux system I am configuring. Through some research I've found the way I might want to do it is use udev rules to run a script, ...
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49 views

Why does rename() take longer when fsync() is called first?

In this test, why does rename() take longer when fsync() is called first? Environment: btrfs, mechanical HDD, Debian 9 container, running on kernel 5.0.17-200.fc29.x86_64. Test command: dpkg -r ...
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Debian Kernel Upgrade Issue

I have been trying to update the kernel (it's an OpenVZ VPS), but even though going through the procedure, uname -r returns 2.6.32-042stab132.1 and hostnamectl returns the following output now: ...
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Linux system process activity suspended

Introduction: I am running a cpp application on an embedded systems device with onboard Linux, which gathers sensor data, prepares it into a JSON formatted string payload and publishes the payload on ...
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118 views

How does the ELF loader determine the initial stack size?

I'm studying the ELF specification (http://www.skyfree.org/linux/references/ELF_Format.pdf), and one point that is not clear to me about the program loading process is how the stack is initialized, ...
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cgroup IO control v.s. (the new types of) Linux AIO

In Linux v5.0, do some types of Asynchronous IO bypass the cgroup IO controllers? EDIT: buffered write() and fsync() might be relatively complex to analyse. I found an interesting post about ...
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1answer
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SHMMAX + how effected kernel parameter that not set correctly by mistake

few words about shared memory Shared memory allows processes to access common structures and data by placing them in shared memory segments. It is the fastest form of inter-process communication ...
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access to sysfs data inside kernel module

I need battery properties for a custom kernel module. this data is mounted in sys/class/power_supply .I know all the discussions about why one should not read/write files from kernel and a solution ...
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1answer
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Using Swapfile for Hibernation with BTRFS and Kernel 5.0.16-gentoo

I created a swap file as described here: https://wiki.archlinux.org/index.php/Swap#Swap_file_creation When I try to hibernate I get the following error: $ echo disk > /sys/power/state echo: write ...
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1answer
58 views

Why ip_forward is disable by default? any side effect?

I need to forward an interface and I wonder why is disable by default? There is any security issue when I enable it? Is there any side effect when I enable it?
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Kernel not detecting system files

I'm currently part of a small team developing a kernel for an Android wearable. We're tempting to add NFC support to a smartwatch which has the hardware required, just no kernel or Android support for ...
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183 views

What network connections are not seen by netstat/lsof/ss?

Network monitoring tools ss, lsof -i, netstat -ltupw and similar have limitations like namespace and thus they don't show the whole machine connections. (for namespace created with ip we can see other ...
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1answer
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i.MX28 SOC DMA timeout on reading NAND FLASH

I'm porting recent Linux kernel to older existing hardware like the i.MX28 EVK kit from Freescale, and Karo TX28 board. I want to use a part of the NAND FLASH in the file system ("userfs partition" in ...
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/include vs /include/linux in kernel source tree

In linux kernel source, some header files and directories are located directly at /include, but some others are located at /include/linux. Why they just don't put everything into /include? What is the ...
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How writing in debugfs controls ftrace?

Ftrace is controlled by manipulating the debug fs files. But how is it possible ? How kernel be aware of writing in this files and start its required actions?for exmple if 1 is written to tracing_on , ...
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What is a system tool? [closed]

I frequently come across the term system tool, so I wanted to understand the exact meaning of it in Linux. Which of the following three explanations of a system tool in Linux is correct? Is a system ...
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Struct structure with method in linux source code [migrated]

I am reading android kernel code and I'm facing this kind of data structures , static const struct file_operations tracing_fops = { .open = tracing_open, .read = seq_read, .write = ...
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How to check if If i2c-hid and hid-rmi are not used for touchpad?

I'm seeing the following warning in dmesg: [ 2.631179] psmouse serio2: synaptics: Your touchpad (PNP: SYN1218 PNP0f13) says it can support a different bus. If i2c-hid and hid-rmi are not used, you ...
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1answer
47 views

How to upgrade kernel on Pinebook now ARM support is mainlined?

I have a Pinebook with a Quad-Core ARM Cortex A53 64-Bit CPU running the official KDE Neon image with the really old official 3.10 kernel. In 4.17 support for the Pinebook was mainlined, so ...
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1answer
36 views

What happens when user insert command in shell on kernel position? [closed]

In Linux user inserts command on shell like bash or sh, csh something like that. What happens when user insert command in shell on kernel position? Does syscall executes when user execute command? ...