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

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What 4.2 Kernel Optimizations could I make to speed up CR48 netbook?

I have a CR48, had one for years. Love the little grimlin, but it is still a single core machine with the chances of upgrading the processor being slim and none (Even then what looks to be the best ...
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87 views

Error installing kernel from source!

I compiled the latest Linux Kernel (4.5.x) from Linus's git tree. The Kernel compiled perfectly with no errors. After compiling the kernel I installed the modules using sudo make modules_install. That ...
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1answer
71 views

How to spoof uname -rs per process

My ubuntu server returns Linux 3.13.0-63-generic when I run uname -rs. From what I found in internet, uname is also a system call which can't be easily overridden when third party program run this ...
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1answer
139 views

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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19 views

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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1answer
54 views

Wacom Tablet (integrated; X201T) disconnects sporadically

I have an X201 tablet with stylus and finger multitouch running Ubuntu 14.04.4 with the 4.2.0 kernel. For no apparent reason, it seems to have an affinity for not recognizing finger (henceforth ...
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3answers
39 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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1answer
69 views

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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25 views

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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1answer
47 views

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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42 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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1answer
35 views

Loop device support on self compiled kernel doesn't work

I compiled 3.10 kernel, I checked that these configuration lines are not commented CONFIG_BLK_DEV_LOOP=y CONFIG_BLK_DEV_LOOP_MIN_COUNT=8 When i'm trying to mount loop device I get this error # ...
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72 views

Kconfig (bool/def_bool/tristate)

In a Kconfig file, what are the differences between : bool def_bool tristate Thank you.
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30 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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2answers
59 views

CPU: 13 PID: 15452 Comm: ssd_blk/0 Tainted: G B I E 3.19.0+ #1

I developed a module which works as an emulator for a block device. When I write into the block device, I get this in dmesg and the module crashes. I cannot get any hint about what is going on? [...
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1answer
32 views

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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0answers
34 views

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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2answers
57 views

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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19 views

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
110 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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1answer
113 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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1answer
75 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 /var/log/...
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2answers
53 views

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 (i.e....
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51 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
126 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 C/...
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1answer
302 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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1answer
78 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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1answer
102 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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248 views

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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58 views

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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1answer
77 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 3.0;...
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94 views

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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1answer
182 views

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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0answers
50 views

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
37 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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76 views

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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1answer
17 views

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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64 views

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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0answers
71 views

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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1answer
45 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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2answers
125 views

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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1answer
58 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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0answers
106 views

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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2answers
180 views

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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1answer
131 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? I'...
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0answers
76 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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RAPL PMU detected, API unit is 2^-32, 4 fixed counters 655360 ms ovfl timer

I compiled my own kernel (version 4.1.5) using the commands: #emerge --ask sys-kernel/genkernel #genkernel all And then I installed grub2 using these commands: #emerge --ask sys-boot/grub #grub2-...
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1answer
70 views

How to dump the dmesg AKA Kernel logs to a single .txt file from the kernel boot?

I am trying to understand the SATA Host-Device Communication and for that I have put a lot of debug messages in the kernel driver code. Now messages are in such a huge amount that I am not able to see ...
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99 views

Manually move kernel image to /boot directory

I have compiled my own kernel on Gentoo (following the handbook) and then I have moved the bzImage to /boot/vmlinuz-4.0.5. But when I boot the system I get the Grub2 shell. What am I doing wrong? ...