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

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23
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3answers
26k views

Why would the kernel drop packets?

I interrupted tcpdump with Ctrl+C and got this total summary: 579204 packets captured 579346 packets received by filter 142 packets dropped by kernel What are the "packets dropped by kernel"? Why ...
1
vote
0answers
19 views

Linux kernel GRUB/boot issue?

I'm working with a specific software package that is only compatible with a older linux kernel version. After installing this older version via the following command $ sudo apt-get install linux-...
0
votes
0answers
13 views

what does yield_task_fair() do in linux scheduler [on hold]

this is a function in linux scheduler, in the implementation of COMPLETELY FAIR SCHEDULER which is in the path: root/kernel/sched/fair.c (link to the file) Now I want to know what does this function ...
2
votes
1answer
16 views

Kernel parameters “console” and “earlycon” refer to old hardware?

I first found this by investigating parameters for earlycon but found that the options for console look almost identical. Both are present below and were taken from this source: From documentation ...
0
votes
0answers
15 views

what does dequeue_task_fair() do in linux scheduler [migrated]

this is a function in linux scheduler, in the implementation of COMPLETELY FAIR SCHEDULER which is in the path: root/kernel/sched/fair.c (link to the file) Now I want to know what does this function ...
1
vote
0answers
11 views

Booting kernel (FIT image) with no rootfs

An embedded Linux device I am working with has the following kernel parameter: root=/dev/ram0 Additionally, the kernel image is bundled together with an initrd and device tree to make a flattened ...
1
vote
1answer
16 views

Does the format or columns of /proc/dev/net change often?

I'm writing a script to scrape some data from this. I'm wondering if this file changes often or is different between distros.
0
votes
0answers
12 views

Error calling EVIOCSKEYCODE

I used journalctl -p 3 -xb and got this error message -- Logs begin at Thu 2016-06-23 22:48:08 AST, end at Sat 2016-06-25 13:15:23 AST. -- Jun 25 09:31:35 Almoullim systemd-udevd[268]: Error calling ...
0
votes
1answer
882 views

custom kernel and firmware loading

After I have compiled my kernel, and when I type make modules_install, not only are the modules copied into /lib/modules/ but also firmware is copied into /lib/firmware/. The following is the end of ...
3
votes
3answers
123 views

How was kernel written? [on hold]

Running a program in kernel mode forbids using standard C library because the only thing your program linked to is kernel itself. So I'm allowed to use functions defined in kernel. But kernel itself ...
-1
votes
0answers
16 views

How to run a function for a specific received packet? [duplicate]

I am doing an experiment for my master thesis. I want to run a function (e.g. multiply two numbers) when a specific packet is received (e.g. a packet with destination TCP port 6666). For example, I ...
0
votes
0answers
10 views

I'm unable to further install solus 1.2

Because once i enter the installation process it is automatically having an higher resolution than what my monitor can support. What changes can i make in any kernels to make the installation process ...
1
vote
1answer
31 views

Embedded Linux OOM - help with lost RAM

I have little Linux system with 256MB RAM. I'm little bit confused, where the RAM may be lost? It is running old linux kernel 2.6.38 and I'm not able to ubgrade it (some specific ARM board). SHM and ...
0
votes
0answers
26 views

Force dirty pages limit in kernel sources

First of all, I'm not sure if that's a solution to my problem. My problem is that during I/O embedded linux is allocating too much memory in cache causing OOM if I run anything else. I/O operations ...
4
votes
1answer
29 views

Why does reading /proc/net/tcp take a long time ss is quick to return the same sort of data about the connections table?

On Linux 2.6.32, if you read (for example, cat) /proc/net/tcp, on a very loaded system (for example, a web server), you will find that reading 100K entries takes over 30 seconds. That's a long time. ...
6
votes
3answers
865 views

Asus X101H - Touchpad not recognized (want to disable while typing)

I have been struggling with this issue for a while and have done an exhaustive search for answers here and elsewhere before posting this question. On my Asus X101H, the touchpad is not recognized as ...
140
votes
1answer
309k views

How do you empty the buffers and cache on a Linux system?

Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache? Note that this is mostly useful for benchmarking. Emptying ...
1
vote
1answer
122 views

Why kernel may be throttled?

My MBR start freezing up for over hour and I've found that my kernel reported being throttled, e.g. (this is just a sample for 2 seconds) $ sudo fs_usage | | grep -i throttled 12:26:45 THROTTLED ...
1
vote
0answers
44 views

What happens if dbus connection fails?

I am trying to find a root cause for server hung. I found that a process crashed with process id 14900 and the following are the log in message. No core dump is saved as it is not related to any ...
8
votes
2answers
2k views

An oom killer thats baffling me

I am not able to understand why would kernel issue this oom killer when I see enough memory is available: Also why are there so many kernel cache pages allocated? I say enough memory is available ...
0
votes
1answer
590 views

NFS: failed to create MNT RPC client status = -101

I am trying for network file system (NFS) booting between two systems. I am using dhcp server to assign IP-address for client. And my kernel and root file system are present in server. My client is ...
3
votes
1answer
8k views

After installing a new Kernel in Ubuntu 14.04, rebooting takes me to busybox initramfs. How do I mount a filesystem after that?

I have a virtual machine with Ubuntu 14.04 in it. I recently built and installed linux-3.14.5 kernel on it, and tried to boot into it, but it drops me to BusyBox v1.21.1 built-in shell. Here's what I ...
1
vote
0answers
110 views

new kernel compile - error on bootup - Could not find overlay

I was compiling the kernel using slackware-current, the latest version of the kernel, 4.3.3, also tried 4.4-rc5, and ran into this error on bootup Could not find overlay #6 ### dt-test ### of ...
16
votes
4answers
950 views

How to force Linux kernel to “freeze” (or nearly freeze) for a few hundred milliseconds

We are running a real-time process on a non real-time kernel (CentOS 6), and this is probably not going to change. We have a streaming video application that requires about 500 MB/s of PCIe traffic ...
1
vote
1answer
36 views

Linux video capture does not work cam3 or Image capture in cam1 fails

I am trying to some solution or run-time fix on this. Problem: After connecting a 3rd camera, Linux video capture does not work cam3 or Image capture in cam1 fails. History: Initially, we ...
0
votes
0answers
6 views

How to make selinux on Android kernel, permanently permissive? [migrated]

I am new to kernels and lately i compiled one for galaxy s5 with the marshmallow opensource. Now i can change my selinux policy to permissive from terminal emulator but i want to make that permanent ...
3
votes
1answer
27 views

WiFi card disappears after reboot, but not after cold boot

I have an Arch-based server (Zotac Nano, AMD Kabini-based) which doubles as WiFi access point using a miniPCI Atheros WiFi card. If I start it form cold boot (as in “it was off”), then everything ...
6
votes
1answer
466 views

How do I quickly build and test the kernel if I want to modify a system call

In particular, I'd like to add a fd flag and a branch in a couple of fd-handling syscalls that should be used if the flag is set instead of the current code. I think the only thing that matters here ...
1
vote
1answer
967 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 ...
34
votes
2answers
30k views

What is difference between User space and Kernel space?

Is Kernel space used when Kernel is executing on the behalf of the user program i.e. System Call? Or is it the address space for all the Kernel threads (for example scheduler)? If it is the first one,...
1
vote
1answer
14 views

modprobe events not logged in /var/log/messages

I'm trying to understand Linux better, specifically driver registration and such so I'm trying to follow what happens when I insert modules and drivers. From what I thought I understood, kernel ...
0
votes
0answers
33 views

linux + dose each security kernel rpm will install the relevant initrd and vmlinuz files under /boot

I just print the kernel rpms that need to install on my redhat machine (version 6.5) # yum list-security --security | grep kernel-[0-9] RHSA-2014:1143 security kernel-2.6.18-371.12.1.el5.x86_64 ...
4
votes
1answer
111 views

Loading WiFi driver results in the whole system becoming unstable. How to debug?

I am not a linux kernel expert, but I got this new laptop and it's WiFi(RT3290LE) is not working. I tried solutions from various sources and they are not working. So it is upto me to solve it, and I ...
6
votes
2answers
1k views

Benefiting of sched_autogroup_enabled on the desktop

I am running a 2.6.37 kernel with sched_autogroup_enabled set to 1. I am not certain that I am seeing the benefits of this patch since: I am launching my applications from the desktop; applications ...
4
votes
3answers
722 views

Kdump.service FAILED centOS 7

I'm having CentOS 7 64 installed on my desktop. After recent system update, I am getting below error while booting the CentOS 7. Some time system is able to boot and I can work on it. but it gives ...
1
vote
2answers
617 views

Kernel Panic dumps no log files

I was playing a game on Steam and all a sudden I got a kernel panic, I manually shutdown the computer and booted back into Linux Mint 17.1 (Cinnamon) 64-bit, and went to go check through my log files ...
0
votes
1answer
32 views

why local CPU must have interrupts enabled, otherwise kernel preemption is not performed?

I read the book "understanding the Linux kernel". I cannot understand a sentence,that is ,the local CPU must have local interrupts enabled, otherwise kernel preemption is not performed. What is the ...
4
votes
1answer
4k 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 ...
98
votes
6answers
154k views

How to reload udev rules without reboot?

How should one reload udev rules, so that newly created one can function? I'm running Arch Linux, and I don't have a udevstart command here. Also checked /etc/rc.d, no udev service there.
1
vote
0answers
36 views

Can you set Linux sysctl values at compile time

I am compiling a custom linux kernel. I want to set some sysctl values at kernel compile time. Defaults I want are different to the defaults kernel sets. Is there a way to do this? Please note I ...
3
votes
0answers
23 views

Is there a tablet SOC capable of running a blob-free mainline Linux kernel with open wifi, and useable graphics support? [migrated]

I am wondering, whether a platform with these specifications exists: Hacking-friendly from open boot-loader up (support for re-locking?) Linux mainline kernel (blob-free?) boot support with SMP. ...
1
vote
1answer
19 views

Kernel and User space System Calls [closed]

I understand some complex internal of OSes, but I have a large gap in understanding kernel and user space. I will explain how I understand this now. First of all we have RAM for example 8GB, ...
1
vote
1answer
86 views

Unable to verify the kernel signature “gpg: Can't check signature: public key not found”

In order to compile a new kernel on my Debian jessie, I am trying to verify the GPG key , following the instruction on the official website. I have download the the linux-3.18.35.tar.sign and linux-3....
0
votes
0answers
32 views

Can't mount fdescfs to /dev/fd

Hello I can't mount fdesc,here is the output root@nshost2:~ # mount -t fdescfs fdesc /dev/fd mount: fdesc: Operation not supported by device And here is the output of dmesg root@nshost2:~ # dmesg |...
2
votes
3answers
61 views

Why do we need initramfs and initrd

I understand the purpose of the this concept. For example we have exotic file system on the disk and in order to load system we need mount root filesystem. But we cannot because there is no suitable ...
0
votes
0answers
24 views

redhat + how to install only the latest kernel from kernel security packages

I am not sure but I found the installonly_limit parameter from yum.conf when we set installonly_limit=1 , Dose this mean to install always the latest kernel ? for example if security packages ...
2
votes
1answer
45 views

What are linux long term support kernels?

I'm running an arch linux server and recently switched to an lts kernel from the repositories. Since I'm not rebooting the server very often, I want a stable kernel that is supported for a very long ...
1
vote
1answer
48 views

Why is /lib/modules so huge under my gentoo, compared to Ubuntu

I have a Gentoo installation. For compiling the kernel I used the configuration from Ubuntu 14.04 kernel. I find it hard to understand why the sizes of the modules libraries are so different: In ...
0
votes
1answer
40 views

grub2 + how to print the current index according to grubby --info=ALL

how to verify in linux 7 , what is the current index that have the current kernel version for example I want to know if the kernel - 3.10.0-327.18.2.el7.x86_64 is located in index=0 or index=1 or ...
2
votes
0answers
54 views

how to capture the latest kernel version from grub.conf

how to capture the latest kernel version from grub.conf ( in case default=0) for example the latest kernel from the file is 2.6.18-409.el5 # all kernel and initrd paths are relative to /...