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

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How to Downgrade CentOS 7.2 to 7.1 on Linode?

I can change Kernel on Linode Manager page, but I don't know how to Downgrade CentOS 7.2 to 7.1
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ip_local_port_range kernel parameter confusion

On my system we have following setting: [root@voip ~]# cat /proc/sys/net/ipv4/ip_local_port_range 32768 61000 We have asterisk running on it which is using RTP port range 12000-13000 in case we ...
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3answers
34 views

Updating kernel but not packages

I need to update the kernel from version 2.6.30 to 2.6.37. I'm going to just compile the kernel and kernel modules for this architecture and boot it. But also there are a lot of packages installed, ...
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3answers
418 views

Why do people call Linux a kernel rather than an OS?

Why do people refer to Linux as a kernel rather than an operating system? To the best of my knowledge, the kernel is one part of the operating system.
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What part of TTY subsystem control the active /dev/ttyN (TTY device driver N)? [closed]

TTY subsystem contains TTY driver, line discipline and hardware drivers (keyboard driver, display driver). Let's say I use a virtual terminal/console. So, my current session uses /dev/tty1 (TTY driver ...
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bash's pseudo terminal master [duplicate]

I learn when we use pts, there is master of pts. Then, when we type the characters on the pts(which is the terminal of bash), not only the output of bash goes to pts but also its master? I confirm ...
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2answers
1k views

how do I safely delete old kernel versions in CentOS 7?

I might be encountering odd symptoms resulting from competing kernels in CentOS 7. So how do I safely delete the old kernels? And how do I know which kernel is the newest one? Below is the ...
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571 views

Removing the rescue image from /boot on fedora

I am trying to upgrade my fedora system (21 → 22) using fedup. I removed all old kernels using package-cleanup but fedup still needs 2MB more on /boot. These are the files in /boot: -rw-r--r--. 1 ...
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Cannot compile a linux kernel for an ARM board [closed]

I am trying to compile a linux kernel (2.6.32.70) for an ARM board (versatilepb), it is my first steps in embedded linux. At the end of the compilation, two compressed kernel images are generated ...
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4answers
1k views

What exactly happens when I execute a file in my shell?

So, I thought I had a good understanding of this, but just ran a test (in response to a conversation where I disagreed with someone) and found that my understanding is flawed... In as much detail as ...
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27 views

Help debugging a kernel oops

My system has been freezing up for a while, and I keep seeing this particular kernel oops: syslog. Xorg.log Here's another similar crash from a few months ago. syslog Can you help me debug this? How ...
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649 views

Cannot mount eCryptfs

I tried to install eCryptfs on my server to open an eCryptfs I did on my home computer. I got these errors. $ sudo mount -t ecryptfs /home/(place)/enc/ /home/(place)/enc/ Unable to get the ...
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35 views

Block device disappears after suspend-resume

After few suspend/resume cycles one of my hdd disappears from the list of devices, here is part of dmesg output that seems to be related to issue: [ 450.005310] sd 5:0:0:0: [sdc] Starting disk [ ...
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78 views

Is there a general USB 3.0 support in OpenWrt?

the only information i found about this topic is outdated since 2011/02: it says there is no support for devices with usb 3.0 "so far"! according to the german wikipedia since version 2.6.30 the ...
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24 views

perl script stall nanosleep() call in strace output

I have perl base SIP client which calling for SIP REGISTRATION process but i am seeing it stall for 10 second at nanosleep() call send(4, "REGISTER sip:sip.example.com S"..., 513, 0) = 513 select(8, ...
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1answer
65 views

Desktop completely freezing on I/O operations

In my old system, I was already having desktop freezes on some heavy I/O operations like apt-get dist-upgrade and copying 4 GB video files. But now, it has become a lot worse: any apt-get install is ...
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59 views

Unable to boot a kvm guest via qemu/kvm-tools

I am using ARM Foundation Model to emulate a arm-v8 environment(I need both TrustZone and KVM), and I run a kvm-enabled linux on it as the Host OS, the kernel version is 3.14.0(I clone it following ...
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How do I know which File Systems my linux supports? [duplicate]

I am working with linux 3.19.0+ and I want to know if my linux kernel supports f2fs (Flash-Friendly File System). How do I know that?
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How to switch static drivers like switching kernel module drivers?

I have a linux embedded device that I need to switch between USB file storage gadget driver and USB Ethernet gadget driver at runtime. The approach I use now is to build both drivers into kernel ...
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1answer
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How can strace monitor itself?

I have a Hypothetical Situation. (1) Let us say we have two strace Processes S1 & S2, which are simply monitoring each other. How can this be possible ? Well, in the command-line options for ...
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What is the role of these RPM packages( kernel-debuginfo and kernel-debuginfo-common RPMs, and the kernel-devel RPM)?

I want to know what the role of these RPM packages( kernel-debuginfo and kernel-debuginfo-common RPMs, and the kernel-devel RPM)?
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1answer
230 views

How to explain strange kernel messages?

I have a server running on Debian Wheezy 3.2.68-1+deb7u1 x86_64. Lately strange records in /var/log/messages appeared. First messages of this log starts just after server reboot. 6.222.18 LEN=44 ...
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1answer
9k views

Centos 7.1 still using outdate kernel 3.10 how to upgrade to kernel 4.0

I'd like to upgrade my Centos 7.1 kernel from 3.10 to 4.0 i did successfully in Ubuntu 15.04 using Linux 4.0.1-040001-generic even though i updated it manually it's works fine so please could ...
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1answer
62 views

Linux + how to know why Linux machine is hung from the messages on the console

As the picture below , my VM Linux machine was hung and I cant login how to identify the reason for the "hung" according to the messages on the console? I also searched more info from the ...
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2answers
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Efficient way to deploy a custom kernel onto multiple hosts

I recently had to do a custom build of the Linux kernel from its source. That custom kernel is now installed on the machine I used to build it and works fine. Now there are other similar systems ...
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41 views

module not loaded at boot

I'm on an archlinux 4.4.1-2 and I'm trying to set up a netctl service. Problem is that for netctl to work I need to have bcma and b43 loaded. Since these two are not out-of-tree modules I thought I ...
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2answers
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Module vfat fails to load (I've tried the obvious fixes)

The module vfat doesn't load on boot, and attempts to force the issue with a modprobe vfat produce the error modprobe: ERROR: could not insert 'vfat': Unknown symbol in module, or unknown parameter ...
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26 views

How to interpret some kernel OOPS output?

I'm trying to analyze some kernel OOPS message. I'm able to understand most of the output, but there's still some lines that I have no idea how the should be interpreted. The first thing is PGD which ...
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1answer
68 views

How does linux load firmeware for built-in driver modules

I've learned that the firmware-subsystem uses udevd to copy a firmware to the created sysfs 'data' entry. But how does this work in case of a built-in driver module where udevd hasn't started yet? ...
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67 views

CentOS 7 unable to cleanly umount a bind mount using rbind and rslave

The following sequence of commands will fail on CentOS 7 (kernel version: 3.10.0-327.10.1.el7.x86_64): [hidden]$ mkdir -p A B/a C/b [hidden]$ sudo mount --bind A B/a [hidden]$ sudo mount --rbind B ...
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127 views

Find Linux kernel build date/time?

In a Linux distro, let's say Ubuntu 14.04, how can one find the time and date when this particular Linux Kernel was compiled/built?
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60 views

why process running in kernel mode cannot be preempted [duplicate]

I read that user mode process are preemptive but why not kernel mode process?
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Differences between system processes, and user processes, kernel control paths and kernel thread

My understanding is that a process always runs in user mode and uses user space only, and a kernel always runs in kernel mode and uses kernel space only. But I feel that I might not be correct, ...
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2answers
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How to find out the reason why ssh processes are hanging?

When I run command like iostat -dkx 2 2 via ssh, I get the expected result, but the processes on the local computer are saying alive in status "interruptible sleep". Why is this happening? Is there a ...
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How does vfs_write decide to aio_write of which file system?

We know that sys_write call vfs_write that ultimately call fs->f_ops->aio_write.But how does kernel know which filesystem's aio_write call back function to call?? Moreover I have noticed that ...
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69 views

Why are Linux versions so confusing?

I was browsing through kernel.org pages and reading changelogs from several different Linux kernel versions. I noticed the version number pattern is extremely awkward: From Linux 2.6.x came Linux ...
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How to Modify Android Boot Sequence in Order to Boot From an SD Card

I've been looking into how to boot Android form an SD card, and I came across this thread on XDA, but I am too much of a noob to understand it, and user has stated that she doesn't have the time to ...
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Mysterious 8 second delay in boot after grub

I have installed Fedora 23 (KDE spin) on an HP Prodesk mini 600 G2. There is one problem I can't quite figure out, though: after grub comes up, and I press enter on any kernel to boot, the screen goes ...
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1answer
35 views

Linux setup compatibility

I want to setup a Linux environment, but I want the system to be bootable in two or more computer systems with different sets of hardware. Can Linux provide that level of hardware abstraction given ...
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55 views

FIPS mode, signature verification failed

I am building a kernel with FIPS mode on. I followed most of the procedures described on Red Hat documentation here. I also created a hmac signed .vmlinuz file. After installing dracut-fips and ...
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1answer
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Abrupt Loss of Brightness Control

So I've had an openSUSE 13.2 (kernel 3.16.7-29) installation running on an Acer Aspire S7-392 for well over a year and have no problems until Sunday. I can't recall if I did an update or what, but I ...
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bcache not working as expected with ramdisk as cache device

I was trying out bcache but i don't have an SSD so wanted to use free memory as a substitute. As ramdisk is listed in /proc/devices as block device i assumed this would work OK but with below simple ...
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How to detect rootkit linux kernel module based?

I found this small rootkit source code implemented as a Linux kernel module. https://github.com/mfontanini/Programs-Scripts/tree/master/rootkit Basically, as you can see, it changes the ...
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What's different between logical block and physical block?

I know the logical block is viewed by kernel, and physical block is viewed by disk controller. Then, Where the file system like ext3's block is related? Is this logical or physical? I think file ...
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1answer
36 views

How to capture my screen video stream?

I try to capture the output of my gpu, the video flux of my desktop, to stream it on another computer. I'm working on a project like a remote control terminal so I can't have any latency. I have ...
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3answers
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kernel configs and dependencies

When a particular kernel config is turned on, e.g. CONFIG_CRYPTO_FIPS=y a bunch of other dependencies (CONFIG_XXX_YYYY) get turned on during compilation. Is there a way to know all the dependencies ...
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14k views

How to get back from “testing” to “stable” - Kernel downgrade

currently I am having lot's of fun with apt-get - and the bad thing is, it was my own fault. I had enabled the testing packages in /etc/apt/sources.list to install a certain package. And I told my ...
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2answers
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what means 'processor execution level'?

I'm reading about Unix in a book "The design of UNIX operating system". But, in the text middle of process state (e.g wakeup, interrupt), there is term 'raise processor execution level'. What does ...
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Error booting kernel 4.5.0-rc1 on Encrypted HDD

I cloned the Git tree of the mainline Linux Kernel and compiled it(version 4.5.0-rc1). After compiling with default configuration (make defconfig) I installed it. In the grub menu I can select this ...
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4answers
5k views

Given vmlinuz and initrd.gz, how do I find out, where the kernel is going to load / (root) file system from?

I'm trying various ways of Linux installation (from iso, flash, iso on flash, kernel on flash, root FS in iso-file on flash...) and want to understand what's going on. My question is: is it possible, ...