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

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QT application doesn't receive udp broadcast since linux kernel 3.13.0-70

I'm developing a QT application on Ubuntu and suddenly had problems because QT app doesn't receive UDP broadcast messages. They are visible in Wireshark on that machine, but never received in QT. ...
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23 views

Bridging two interfaces with iproute2 doesn't work

I'm trying to create a bridge between eth0 and eth1 with iproute2, but there's always the error: RTNETLINK answers: Operation not supported when I use the command:ip link add name br0 type bridge. ...
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Having a bad time installing Ubuntu

So, I recently upgraded my motherboard and processor. Windows was a real pain to me so I decided to go with Ubuntu. However, I ran into more than a few problems with my installation: When I tried ...
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1answer
33 views

After my system crashed and I run crash, but I get the following error: not a supported file format

My system crashed and even though I haven't been able to know what caused the crash after going through the usual logs: messages, dmesg, secure, etc. There's nothing valuable I have seen on them so I ...
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5answers
43k views

What are high memory and low memory on Linux?

I'm interested in the difference between Highmem and Lowmem: Why is there such a differentiation? What do we gain by doing so? What features does each have?
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1answer
5k views

Real time processes scheduling in Linux

I have been learning some scheduling concepts. Currently my understanding so far is as below. There are real time processes and non real time processes. Non real time processes can have nice values ...
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36 views

ip link add gives me an error that it's not supported

I would like to set up a bridge with iproute2 like this: Adding bridge : ip link add name br0 type bridge Bringing bridge UP : ip link set dev br0 up Adding interface to bridge : ip link set dev eth1 ...
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28 views

Ubuntu DMA Auto Activate Optimization Flag

I have two NAS devices, which differ in architecture. They are connected to the same SATA disks and one of them shows better read and write performances. Okay, there could be many reasons for such ...
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1answer
24k views

What is kernel ip forwarding?

I have seen on many blogs, using this command to enable IP forwarding while using many network security/sniffing tools on linux echo 1 > /proc/sys/net/ipv4/ip_forward Can anyone explain me in ...
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Assign virtual core number to specific real core

Is there any way to assign ''linux core numbers'' to specific real cores? I'm working with an asymmetric architecture, so not all cores are the same, and I want to assign specific cores number to ...
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5answers
16k views

Why is kworker consuming so many resources on Linux 3.0.0-12-server?

Last Friday I upgraded my Ubuntu server to 11.10, which now runs with a 3.0.0-12-server kernel. Since then the overall performance has dropped dramatically. Before the upgrade the system load was ...
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2k views

Automatic kernel configuration tool

Is there any developed automatic linux kernel configuration tool? I have found a method of make localmodconfig, but it is certainly very limited. I have searched the web but unfortunately have not ...
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What can interrupt execution of threads which are pinned to cores?

I do low-latency application development and I use isocpu and set thread affinity to reduce (eliminate?) context switching during my critical threads. However, I am unsure what other types of ...
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1answer
750 views

Kernel module blacklist not working

I'm trying to figure out how to blacklist modules, and I'm trying it on the usb storage. Unfortunatelly it seems ot have no effect, and I get the module in even if it's not used (apparently). My ...
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3answers
1k views

Error installing kernel on Centos (from source)

I am running GNU/Linux (Centos 6) on kernel 2.6.32-431.17.1.el6.x86_64. I am trying to update the kernel to 3.2.61. I performed the following steps inside the 3.2.61 folder structure: make ...
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2answers
5k views

“Argument list too long”: How do I deal with it, without changing my command?

When I run a command like ls */*/*/*/*.jpg, I get the error -bash: /bin/ls: Argument list too long I know why this happens: it is because there is a kernel limit on the amount of space for ...
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1answer
51 views

View current kernel parameters?

I saw in my syslog kernel.perf_event_max_sample_rate get changed. I was wondering if I could write a quick script to log this variable every few minutes. Currently it is: sysctl -a | grep ...
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1answer
38 views

Why are there module options AND driver options - e.g. for the i915 module?

The i915 Kernel module has several "module options" like the infamous enable_rc6. However, for the xorg config file, there are further options such as TearFree. I was wondering - why are there two ...
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Diagnosing regular crashes with data loss?

I'm on Kubuntu 15.04 on a HP zBook 14. Every few days, my computer locks up completely - screen stays on, sound get stuck and plays the last few tenths of a second of what ever was playing over and ...
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179 views

Installing Linux onto Teclast X80H x86 tablet

I'm trying to install Linux (any linux, but preferrably Ubuntu Mate) onto my cheap tablet Teclast X80H, which came preinstalled with WIN8/Android x86. Main specs are: CPU: Intel Bay Trail, 1830 MHz, ...
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63 views

Why cgroup cpu items are miss in Debian 8

the kernel version for debian 8 use 3.10. But under /sys/fs/cgroup/cpu, miss a lot of cpu items. vagrant@debian-jessie:/sys/fs/cgroup/cpu$ ls -1 . cgroup.clone_children cgroup.procs ...
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1answer
78 views

Kernel update - reboot needed or not?

I just updated our AWS Linux Server (which uses yum) and a new kernel is installed: kernel-4.1.10-16.27.amzn1.x86_64. It didn't state anything about restarting. According to this answer here I ...
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no bios, black screen on laptop after kernel upgrade and hibernation

I am running dual boot Windows 7 and Linux Mint 17.2 on an ASUS K56. I upgraded the kernel to 4.2 the other day. Reboot and everything worked just fine. Tested browser, music player etc. Then I leave ...
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2k views

Compare two kernel config files from the menuconfig perspective?

I have a situation in which i have two kernel config files (for the same kernel source ). Both of them have a part of the functionality that i need (on one, USB works correctly, on other, the second ...
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29 views

sysfs alternative to /proc/acpi/button/lid/LID/state

As you probably know ACPI procfs is deprecated in new kernel versions and with sysfs I don't know of a clean way of reading the state of the lid button. The only way I've come up with is hooking up ...
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335 views

RTC time synchronization not working (CONFIG_RTC_SYSTOHC)

I have the option CONFIG_RTC_SYSTOHC enabled in my kernel: Device Drivers ---> [*] Real Time Clock ---> [*] Set the RTC time based on NTP synchronization The help says: ...
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2answers
767 views

When will Debian switch to Linux 4.x?

Wikipedia says that current Debian 8.2 Jessie is based on kernel 3.16.0, so I was wondering when a native version based on kernel 4.x would be released and if the live kernel patching will be there as ...
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27 views

How do I configure a systemd service to execute simple /bin/echo “Hello world” command to show the output on the console?

I am trying to boot up a vm with qemu-system-ppc64(similar to lkvm). I am using the following command: qemu-system-ppc64 --enable-kvm -vga none -nographic -nodefaults -chardev stdio,id=id1 ...
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1answer
515 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 ...
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1answer
65 views

Appending files to initramfs image - reliable?

I'm modifying a bunch of initramfs archives from different Linux distros in which normally only one file is being changed. I would like to automate the process without switching to root user to ...
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1answer
30 views

How to find hugepage size on system?

I am getting following two different result. which one i should consider for Hugepage? [root@server ~]# getconf PAGESIZE 4096 [root@server ~]# grep -i hugepagesize /proc/meminfo Hugepagesize: ...
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Why number of dirty pages is always 0 on 2.6?

In /usr/src/linux/Documentation/filesystems/proc.txt i've found the string: Table 1-3: Contents of the statm files (as of 2.6.8-rc3) ...
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Unable to view printk output

I have been trying to debug my kernel code with printk statements. But the messages does not show up on the console. cat /proc/sys/kernel/printk gives 7 4 1 7. What could be the reason?
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Kernel inotify watch limit reached

I'm currently facing a problem on a linux box where as root I have commands returning error because inotify watch limit has been reached. # tail -f /var/log/messages [...] tail: cannot watch ...
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1answer
29 views

passing file in mount options

I am writing a stackable file system which requires some database file. I am thinking of taking it as mount time argument and then reading it's content into private field of superblock of mounted FS. ...
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Map non-standard hid reports to scancodes for Logitech G105 Gaming Keyboard

So, I've recently purchased the named keyboard and have been doing some reverse engineering as to how the Logitech Gaming Software does things with it. In this process I've discovered that a few magic ...
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1answer
77 views

module issues with kernel

I am currently getting this error message:- iptables v1.4.12: can't initialize iptables table `filter': Table does not exist (do you need to insmod?) Perhaps iptables or your kernel needs to be ...
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2answers
32 views

Only booting to GRUB automatically

I installed Elementary OS earlier as the sole OS on my machine. When I boot now, GRUB is displayed on the screen (with a message about minimal bash being available). I can boot to Elementary OS by ...
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Microkernel (e.g. GNU Hurd) more secure than monolithic kernel (Linux)? [duplicate]

I would like to understand (in relatively layman's terms) if and how a microkernel such as the Mach-based GNU Hurd is more secure than a monolithic kernel such a Linux. Additionally, does a ...
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35 views

Automated kernel recompilation on security patches?

I'm on Ubuntu 14.04 and really enjoy the fact that I get automatic kernel security updates. When a kernel security problem is patched, a new package will be shipped with the new version. My machine is ...
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1answer
90 views

How can Kernel 4.0 patch the system rebootless?

I've seen that new functionality mentioned in Linux kernel 4.0 was the ability to update without a reboot. Does this mean I can use my system with my application going, and the update will have no ...
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1answer
258 views

What's changed with USB drivers in 4.0 and later Linux kernels?

With kernels up to 3.19, all of my USB devices work perfectly. On upgrading to 4.0 or later, some of my USB devices stop working and the kernel produces errors like this: [ 3.369436] usb 9-1: ...
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2answers
3k views

What is the difference between likely and unlikely calls in Kernel?

What is the between likely and unlikely calls in Kernel. While searching through the kernel source i found these statements. # define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) ...
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1answer
307 views

loading ath9k_htc kernel driver fails

could someone please point me in the right direction to get my external wireless stick (TL-WN722N) working on my Xperia Neo (haida) smartphone? So far I've done the following: I downloaded ...
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1answer
59 views

Hairpinning in linux

I have a router in which I installed a Linux system. I want my router supports NAT hairpinning Does a such feature exists in Kernel Linux? If yes how to activate it? Are there a patch to apply it on ...
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1answer
3k views

Your kernel headers for kernel 3.10.0-229.el7.x86_64 cannot be found

When I type the command service vboxdrv setup in my CentOS 7 terminal, I get the following error: Your kernel headers for kernel 3.10.0-229.el7.x86_64 cannot be found How can I resolve this ...
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is it possible to add a Kernel Header file manually along with the kernel source and build

I am using Linux 2.6.18-238.e15. In this kernel source I could not find the kernel header file procinfo.h. But my application requires this header file. Is it possible to add this header file ...
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71 views

Linux Permissions UID 0 vs Ring 0

I am studying for a Computer Security exam, and I am struggling to understand the following sample question. 'Explain the difference between running in ring 0 on x86 and running as UID 0 in Linux. ...
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16k views

What happens when I run the command cat /proc/cpuinfo?

What happens when I write cat /proc/cpuinfo. Is that a named pipe (or something else) to the OS which reads the CPU info on the fly and generate that text each time I call it?
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How do I store the data in disk directly in kernel module? [closed]

I capture the TCP packet in function of netif_receive_skb , I want to store the playload of TCP packet. we can't read/write the file in kernel module, so store in disk directly maybe a way? ...