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Questions tagged [kernel]

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

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Kernel Logical address

Does Kernel logical address go through MMU when used in load/store instruction? Does MMU handle kernel logical address differently from kernel virtual address? Please give reasons for the same. If ...
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1answer
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enable debug for kernel but not systemd

I have added the debug parameter on the kernel command line to enable debug in the kernel, unfortunately this also enables debug in systemd causing my /var/log/daemon.log and /var/log/debug to fill up ...
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How do I Get Support for Acer E5-573-54zv Touchpad on a Custom Kernel

I'm compiling a kernel just for learning purpose, and I almost get all things working, bluetooth, hdmi, usb, card reader, webcam, wifi... etc. But I can't make touchpad works, all that I know about it ...
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Gadget mass storage passthrough

I'm using Yocto in kernel 4.14 (computer 1). I have two USB port : Host : with a USB key (mass storage device) plugged OTG : connected to another computer (computer 2) ################...
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Why fork() copy all data the same as parent? [duplicate]

In my understanding, fork() will copy all data to its child, only different is PID. It is strange to me when we want to run a new program, we want a new resource, ex: new free memory space, new ...
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1answer
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Two questions about copy_pte_range() in kernel

I've been trying to understand how fork() works and finally arrived at copy_pte_range(). Most of the functions are understandable but few are quite questionable. Kernel: 4.14.84 static int ...
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1answer
41 views

Mounting is slow after 4000 mounts

I have a need to create about 10,000 total bind mounts for various chroots. After about 3000-4000 mounts, it slows down significantly from 100/s to about 5-10/s. I'm assuming it's hitting some weird ...
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After I enable SELinux, some devices node are unable to be accessed

I enable SELinux feature by configuring kernel (below shows what I changed): @@ -44,7 +44,10 @@ CONFIG_SYSVIPC=y CONFIG_SYSVIPC_SYSCTL=y # CONFIG_POSIX_MQUEUE is not set # CONFIG_FHANDLE is not ...
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1answer
19 views

Issue with merging two HDD images into 1

I've got two HDD image files, which both of have 2 partitions each. On each image, the first partition is the grub boot partition, and the second partition contains the files and kernel. The second ...
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3answers
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who run main() of linux?

In Linux 0.11, we can see there is a main.c with a main() In my understanding, the object code needs an OS to run it. I mean, since Linux 0.11 is an OS, who is in front of it to run it? DOS?
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1answer
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Syslog to console, drawbacks?

I am wondering are there any drawback (performance wise) when output from some software is not logged to a file, but instead to console? Specific case would be running Docker containers, as some of ...
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1answer
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How long time does a context switch take in Linux (ubuntu 18.04)

I'm interessted in getting the number of context switches a two processes in a KVM vm takes on a singel CPU over some time. Earlier i have used perf, is this best practice? And how much time is used ...
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2answers
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if some files are pseudo, why open() function still can access it?

We know there are many files that are pseudo files, i.e. not a real file. ex: /sys/xxx /proc/xxx /dev/xxxx In my understanding, the open() will call x86 ASM code, the ASM code will do hardware ...
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How does Top process manager get memory information? [closed]

I am trying to learn about the Top process manager for Linux. I am trying to understand how Top gets its memory information. So far I have found some memory code in Top.c and Top.h to display the data ...
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2answers
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Best method for searching linux kernel changelog from 4.18.0 to 4.20.16

My question is similar to this question: Where to find the Linux changelog of minor versions But I would like to search all changelogs from 4.18.0 to 4.20.16 for any reference to a specific word, ...
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1answer
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Linux mint exhibits wifi issues after upgrading kernel to 5.0

After I have upgraded the kernel to 5.0.0-050000-generic, whenever I log in my laptop after it was in standby. The wifi stops working and I need to reboot the system. I would like to downgrade to ...
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Want to know the reason for “Kernel: Page allocation failure: order 0 mode 0x201db”

Our ARM Cortex-A5 processor board used at work has been crashing randomly with following journalctl logs. ourApplication.bin[746]: Error: Custom Transport GET failed ourApplication.bin[746]: : ...
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1answer
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kernel error in CentOS 6.9

Recently I see these messeges in my /var/log/messeges and dmesg | less: kernel: INFO: task flush-8:32:1065 blocked for more than 120 seconds. kernel: Not tainted 2.6.32-696.el6.x86_64 #1 ...
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1answer
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Which format is the correct format to use for mkinitcpio.conf?

I am confused about which is the proper formatting to use within mkinitcpio.conf ... I have noticed sometimes double quotes are used and other times parentheses to close off the users desired hooks, ...
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1answer
52 views

Kernel panic - not syncing:VFS: unable to mount root fs on unknown block(2,0)

I have the same Gentoo version installed on 16 machines. Using the same 3 DVDs created in the same way with the same CentOS version and 2 same brand portable DVD-ROMs, I have managed to get the ...
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0answers
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Only 1 out of 2 nvme same capacity ssds is detected on CentOS kernel 4.20 ml version

I have plugged 2 nvme pcie ssd of same capacity on to my dell server running CentOS 7.6 and kernel version 4.20-ml but only one gets detected all the time. While booting from kernel 4.20, an error: "...
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register_netdev() race with ip addr

I am developing a proof of concept for a networking application that uses a generic stack interface driver that connects the stack to a userspace application rather than a physical device. This ...
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1answer
27 views

/proc in Kenrel Modules

Currently I am learning Kernel Module Programming reading "https://www.tldp.org/LDP/lkmpg/2.6/lkmpg.pdf" ,and in that book there is an chapter titled as "/proc File System" , I have learnt how modules ...
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1answer
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dnf upgrade kernel on Centos 7…

On one install, dnf managed to upgrade that kernel. On a newer machine (installed and upgraded today), it fails. Not sure why… Here is a full run: ; sudo dnf upgrade -y Last metadata expiration ...
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Linux 5.0 startup error

It's been just updated from zen custom 4.20.13 to mainline 5.0 ARCH. Damn good work, even 8192cu wireless (rtwn) dkms modules work neatlessly. VBox: perfect! Just got one error message at startup, ...
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1answer
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Why use tristate vs bool in the Linux kernel Kconfig?

Here is my current understanding of why one would choose to use one vs the other, can you please confirm or correct me? Run-time vs compile-time: If you don't know whether or not you want this ...
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1answer
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SLES 12.4| systemd-coredump[<PID>]: Failed to parse resource limit: <daemon_name>

I am using SLES 12.4 VM where I have a custom daemon dumping core frequently as I see from /var/log/messages and coredumpctl. But I never see a core file in /var/lib/systemd/coredump/ or in any other ...
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1answer
59 views

error messages::ext4-fs error(device dm-0) after write-error on swap device

recently, i moved fedora29 into the desktop harddrive from external hard drive (Miraculously, i installed fedora29 on external hard drive anyway ^^:) as installed as soon, it was too slow. i added up ...
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Is it possible to use a phandle of an alias in a device tree overlay?

I have an alias with a phandle I want to use in a cell in an overlay: ublox1:/proc/device-tree/aliases# cat gpio0 | tr '\0' '\n' /ahb/apb/pinctrl@fffff400/gpio@fffff400 If you follow this path, it ...
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linuxmint 19.1: power button inserts letters (works fine on linuxmint 18.3)

I recently did a clean install of LinuxMint 19.1 (MATE edition) on my laptop. Since then, pressing the power button inserts a long row of dddddddddddddddddddddddddddddddddddd until I press it again, ...
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1answer
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Purpose of _LINUX_EXPORT_H macro

What is the purpose of defining _LINUX_EXPORT_H in include/linux/export.h? It seems to be defined in this file and never referenced anywhere else. Is it redundant? Link: _LINUX_EXPORT_H in torvalds/...
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Linux - Failure to assign ipv6 address to virtual interface without error

I'm working on NixOS, creating some functions in C to programmatically manipulate veth pairs and assign IPv6 addresses in order to create a program for setting up a network for containers on a single ...
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Debugging android kernel goldifish emulator under Mac OS Mojave

I need to debug android kernel goldfish under MacOS Mojave. So i cloned android-goldfish-3.18 and android-aosp-9.0.0_r22. I built aosp under macos while the kernel under debian. Obviously I built ...
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Frequent Kernel Panics, how to solve?

I have a HP Laptop, with the following configuration: Intel i7-5500U CPU @ 2.40 GHz NVidia GeForce 940M Intel HD Graphics 5500 8GB Ram I installed Manjaro i3 on it, and am getting frequent Kernel ...
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1answer
73 views

Understanding a dmesg kernel warning message

I am trying to debug my kernel module. When I run it I get the following kernel warnings, but it seems that there is no informative message like other warnings I've seen. Is it possible to get any ...
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Dynamic loading [closed]

How one should implement a dynamic loading system where instead of loading an entire library to the memory, the kernel would load only the necessary function? Considering that each function have a ...
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how to get the program and parent program of do_fork()

I'm trying to make a kernel module that would gather statistics about which process forks what subprocess. Kprobe seems like it might work, but I'm struggling to understand the structs that I get. I ...
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1answer
422 views

How to be safe against CVE-2019-8912?

I've read in news that there is a new Kernel bug https://security-tracker.debian.org/tracker/CVE-2019-8912 Is it safe to use my PC until it gets fixed ? Can someone use this exploit to steal my paypal ...
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Does the main thread of a given process have a Thread Control Block?

If there is a process with a PCB, consisting only of a single execution thread. Does this thread also appear as a TCB?
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Kernel 4.20.8-200 headers?

I'm trying to run VirtualBox on my Fedora 29 machine, but it errors out. Following it's instructions (execute /sbin/vboxconfig) yeilds: Please install the Linux kernel "header" files matching the ...
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1answer
64 views

TUN Module Loaded but OpenVPN /dev/net/tun no such file or directory

lsmod -> tun 16587 0 - Live 0xbf0e1000 Openvpn error: Cannot open TUN/TAP dev /dev/net/tun no such file or directory I tried creating a dummy directory but the error changes to Cannot open TUN/TAP ...
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1answer
87 views

Kernel version in uname differs from version in rpm

In CentOS - the output of rpm -qa | grep -i kernel shows one version (3.10.XX) : kernel-3.10.0-862.14.4.el7.x86_64 kernel-3.10.0-693.21.1.el7.x86_64 kernel-tools-3.10.0-957.5.1.el7.x86_64 kernel-...
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Getting x11 to start on ereader already running a Linux Distro independently on sdcard

I burn a customized recovery image onto a sdcard that gives me ssh and adb access over wifi. I mount the sdcard and successfully get into the Linux Distro image. I enter these commands over adb on ...
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problem with gpu: can't boot

Afterinvoluntary shutdowns of my computer I have been problem with my AMD gpu: kern.log: [rhizome@tensor:~$ cat kern.log | grep 'radeon' Feb 14 10:56:20 tensor kernel: [ 11.412441] [drm] radeon ...
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restrict linux page cache (buffer cache) to only certain address range

Is there a way to restrict linux page cache to only certain address range of the physical memory? More specifically, I want the OS page frame allocator to allocate page cache only to certain addresses ...
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How do i capture /proc/<pid>/stat file of a process | linux kernel

As you may know, the /proc/stat file contain the numbers of ticks the different CPU's have spent their time. Same goes to /proc/pid/stat where the tics are measured based on pid (process id) But when ...
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1answer
92 views

Why does my Makefile not compile and how can I fix it?

I have been having problems compiling a router's kernel for QEMU. I have the router working in QEMU using an OpenWRT kernel, but networking does not work. This is why I want to compile the original ...
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34 views

Tapdev open function returns me 37 value

I am trying to create a tun device and tap interface. But the open function returns 37 value. why? fd = open("/tmp/tun", O_RDWR) https://github.com/contiki-os/contiki NOTE: It works well in my pc ...
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What's the purpose of use_tempaddr=1 kernel parameter?

Reading sysctl docs, I found the following: use_tempaddr - INTEGER Preference for Privacy Extensions (RFC3041). <= 0 : disable Privacy Extensions == 1 : enable Privacy Extensions, ...
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MAC address is removed with tainted VirtualBox modules on Fedora 29

I am getting crash reports. net/mac80211/driver-ops results in drv_remove_interface. My network interface is removed and I can't connect to the WiFi. I can recover this by shutting down or going in ...