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

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mount.cifs : mount error(12) : Cannot allocate memory

I encountered this problem a while ago when upgrading my kernel but put off upgrading until now. On my system I can happily mount network shares using CIFS running kernel 3.7.10, however when I've ...
2
votes
1answer
50 views

What is the difference between all and default in kernel setting? [duplicate]

I want to enable reversed path filtering to prevent source ip spoofing on my server. I noticed that I have the following settings at current: net.ipv4.conf.all.rp_filter = 0 ...
0
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1answer
35 views

How are the different kernel naming schemes relate?

I am running Ubuntu 13.10 with the Kernel 3.8.0-030800-generic downloaded from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.8-raring/ When I want to run for example turbostat or cpupower ...
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1answer
39 views

How to undo kernel settings?

While trying to read some kernel parameters, I think I have mistakenly set some instead: # sysctl --system -r ^net.*tcp * Applying /usr/lib/sysctl.d/00-system.conf ... * Applying ...
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0answers
44 views

How does one clean up a stale CIFS mount

I have a recurring problem where I need to mount a drive of a Win32 machine on my LAN so I can read and write files to it. But I have no control of said machine, and as such, said machine frequently ...
6
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1answer
174 views

Can you explain the entropy estimate used in random.c

/dev/random uses the timings of kernel interupts to add to the entropy pool. The amount of entropy in the pool is tracked in a variable named entropy_count. Here is the relevant snippet of code from ...
2
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1answer
793 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 ...
5
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2answers
1k views

How to know which firmware is loaded by kernel?

I have an Intel wireless card driven by iwlwifi, and I can see the following message in dmesg: iwlwifi 0000:03:00.0: loaded firmware version 17.168.5.3 build 42301 But how do I know which firmware ...
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1answer
6k 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?
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1answer
466 views

Wireless not showing a network in the scan results

I have a weird problem of connecting to a wireless network. I am connecting to a network named "C-202" with WPA-Personal. This network shows up in the scan results some time and won't show some time. ...
105
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3answers
7k views

What does the Windows flag in the Linux logo of kernel 3.11 mean?

I've just installed kernel-3.11.0-1.fc20 for my Fedora 19 installation. During the rebooting progress, I saw the Linux logo with a Windows flag in it, what does it mean? The Fedora 19 is installed ...
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2answers
58 views

what is the difference between Device driver and kernel module

i know that driver is a software that can communicate with the hardware in order to control the device that attached to the computer.whereas kernel module is a small piece of code that can inserted ...
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1answer
28 views

Is there any alternative to genext2fs in RHEL?

I am tryting to make initrd file system following [this tutorial][1] My host system is RHEL 6 64 bit. I am unable to get the required command: genext2fs No rpm is available for it, neither ...
2
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1answer
266 views

What would happen if the amount of free memory (vm.min_free_kbytes) was too low?

I came across the following parameter in kernel settings (in sysctl): vm.min_free_kbytes This is the amount of free memory (RAM) that's always free no matter what. In my case, I have only 1 GiB of ...
0
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1answer
43 views

Is there a way to permanently exclude the kernel from updates?

I'm using Fedora and wonder if there is some way I can exclude kernel updates when I run yum update, until I specifically want to update the kernel. The reason why I am concerned about this is ...
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1answer
97 views

Linux kernel: task vs thread

When I was reading a book(Linux kernel programming), I got interesting/confusing paragraph about mm_segment_t addr_limit(one of the member in struct_task) as below: mm_segment_t addr_limit; ...
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3answers
93 views

how is page size determined in virtual address space?

Linux uses a virtual memory system where all of the addresses are virtual addresses and not physical addresses. These virtual addresses are converted into physical addresses by the processor. To ...
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4answers
370 views

Run command when temperature exceeds threshold, without daemon

I need to run a specific command if my laptop gets too hot (for example, send a STOP signal to Firefox or Virtualbox in order to prevent my laptop from shutting down violently and damaging my hard ...
3
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1answer
43 views

OOM Killer value always one less than set

I am trying to set the oom_adj value for the out of memory killer, and each time I do (regardless of the process) I get back exactly one less than I set (at least for positive integers. I haven't ...
5
votes
2answers
4k views

Can vmlinux be used instead of uImage?

I want to use an uncompressed kernel image and boot the BeagleBoard. Generally I use uImage to boot the kernel which is in compressed format. How do I use an uncompressed kernel image?
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3answers
135 views

Control how linux deletes files

What exactly happens when an application deletes a file? Is there any way to control this behavior? Basically I want to shred instead of rm in all cases, but of course applications do not make calls ...
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1answer
38 views

Getty instances in init process

Init typically will start multiple instances of "getty" which waits for console logins which spawn one's user shell process. Upon shutdown, init controls the sequence and processes for shutdown. The ...
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1answer
29 views

filesystem that works under qemu and I can mount on my host

I'm using qemu for different kind of tasks, I would like to pick a filesystem that is both qemu-compatible and easy to mount under my host. I already discarded both qcow and qcow2 because apparently ...
2
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1answer
252 views

Kernel 3.12 or 3.10? which one has more features, newer and better?

Based on https://www.kernel.org/ kernel 3.12 is released in 2014-04-23 and kernel 3.10 is released in 2014-04-27. Based on release date, 3.12 is older and based on version number 3.10 is older. Which ...
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0answers
69 views

Some questions compiling linux kernel with make-kpkg

I'm doing my first steps compiling the linux kernel and adding a new system call. I've managed to do it, but I still have some questions. For this task, I has set up a Virtual Machine guesting debian ...
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1answer
21 views

Build kernel with multi_v7_defconfig setting

What is multi_v7_defconfig used for and how do I build the Linux kernel with this? I think I can write this into config file as: CONFIG_multi_v7_defconfig=y Please correct me if I'm wrong.
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1answer
98 views

How can I boot with a compressed rootfs?

My problem is: I cannot use compressed rootfs (the kernel crashes during boot) but uncompressed ones work fine. What I did: I'm using Buildroot 2013.11 to generate Images for my embedded Linux ...
0
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1answer
103 views

set permission 0666 on /dev files at boot time

I have to load a few additionals modules. One of them generates /dev/knem file. I have to set the permission to 0666, so a basic chmod 0666 /dev/knem works, but I would like to assign it directly at ...
2
votes
1answer
155 views

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 ...
4
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1answer
203 views

Using a custom name for root device in GRUB

I'm working on old distro ( slackware 8.1 ) using a kernel 2.4.37.9 and I have the following problem. I want to use a custom name for boot device, say for example /dev/root1, which can replace the ...
4
votes
1answer
214 views

kernel: disabling /dev/kmem and /dev/mem

I understand that /dev/kmem and /dev/mem provide access to the memory (i.e. raw RAM) of the system. I am also aware, that /dev/kmem can be completely disabled in kernel and that access can be ...
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0answers
87 views

How can I compile minix when I make changes in libraries

I am looking for a way to compile minix. The make hdboot command seems to do nothing with the directories under /usr/src/lib. I changed only one .c file in syslib. Do I have to do make world for this ...
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2answers
109 views

Upgrading the kernel in Redhat Linux 6.0

How do you upgrade the kernel in Redhat Linux 6.0? And how can I confirm whether it is updated or not?
5
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1answer
247 views

How to specify an ISO as the location of root filesystem for GRUB?

I'm trying to understand the Debian "booting from Hard Disk" installation manual. The process is as follows: I copy a kernel image, a ramdisk initrd and an ISO with installer to the hard drive and ...
3
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2answers
84 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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1answer
45 views

Should I upgrade Ubuntu 12.04 kernel [closed]

I am currently running the 3.5.0.48 kernel on my Ubuntu 12.04.4, and I was wondering whether I should upgrade to 3.8 or 3.11. This makes it seem easy enough. Though I will wait with throwing away my ...
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0answers
61 views

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
70 views

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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2answers
124 views

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 ...
2
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2answers
75 views

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 ...
2
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1answer
294 views

regarding shared memory behaviour

Noticing a strange performance behaviour while using shared memory that are file backed (i.e open user defined file and mmap() the same into process space). While doing a memcpy() into the shared ...
4
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1answer
98 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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0answers
22 views

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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2answers
53 views

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 ...
0
votes
1answer
67 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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0answers
49 views

Passing data from kernel space to user space in FreeBSD [closed]

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 ...
2
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3answers
88 views

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 ...
4
votes
1answer
58 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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0answers
16 views

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 ...
1
vote
1answer
60 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 ...