The kernel of operating systems popularly known as Linux, or sometimes GNU/Linux.

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APEI Generic Hardware Error : PCIe error with ATTO SAS HBA

Recently we upgraded a remote server to a new Dell PowerEdge T630 with dual CPUs (so all PCIe slots are active). It had been running for several weeks fine before we added an IBM LTO5 tape drive that ...
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14 views

SystemTap log output to file

I want to log output from my SystemTap script to a file. But when I try to use the -o option like: stap -r $PWD --remote user@hostname -o test.txt -S 1 ./test.stp I can't find the log file. If I ...
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182 views

Changing the TCP RTO value in Linux

I will like to alter the TCP RTO (retransmission timeout) value for a connection, and some reading I have done suggests that I could do this, but I don’t where and how. I have looked at the ...
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33 views

What is the register %gs used for?

All I was able to find out about the %gs register is, that it seems to be a free to use register on >32bit x86 architectures. It seems that a gs_change is executed before any system-call. Can someone ...
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30 views

Case study of virtual memory management

Need help in understanding virtual memory concept. When a process requesting for 2GB mapping onto the virutal memory in Linux environment of 4GB ( 1GB Kernel : 3GB Userspace), when already another ...
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44 views

What is the impact on system performance when kernel debug info is enabled?

In order to debug kernel or use tools like stap (https://en.wikipedia.org/wiki/SystemTap) kernel must be compiled with full debugging information included - namely option CONFIG_DEBUG_INFO has to be ...
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33 views

bluetooth - btusb module remove stops bluetooth service

I just faced a strange issue; Every time after suspend the btusb module is kicked out the RAM (for some reason but its OK cause I can reinit it manually) but as a result the bluetooth.service must be ...
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1answer
35 views

How does the kernel decides what pages commit to swap?

If RAM usage is higher than the level written in «swapiness», kernel will use SWAP. Ok. But how does the kernel «order» programs? Is it «first come, first served» for RAM? Or biggest programs in ...
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59 views

Kernel memory leak detection [closed]

How are memory leaks identified in Kernel. Not sure if Valgrind can be used in this case.
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Linux Angstrom can't start without serial cable plugged

I'm using the Altera Cyclone V Soc dev Kit and Linux Angstrom provides by rocketboards (http://rocketboards.org/foswiki/Documentation/GSRD141) Kernel is : 3.10 LTSI Linux can't start if any serial ...
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1answer
55 views

How do I detect that my system has auto-rebooted after a kernel panic?

I'm using Linux in embedded systems, and want to configure the system to automatically reboot after a kernel panic. However, when the system comes back up, it's important for me to detect and log the ...
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Telling Linux kernel *not* to use certain CPUs

I'm trying to run some benchmarks on a multicore machine and I'd like to tell the Linux kernel to simply avoid certain cores unless explicitly told to use them. The idea is that I could set aside a ...
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Why is the Linux kernel called an “image”?

I often hear people refer to the Linux kernel as the Linux kernel image and I can't seem to find an answers on any search engines as to why its called an image. When I think of an image I can only ...
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24 views

Trace kernel object calls

We have strace to trace programs, ltrace for dynamic libraries, and others. Is there any equivalent for kernel objects, as in tracing just like strace but for a specific .ko? Thanks
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35 views

High %sy cpu usage , server is very slow

On one of the server we are noticing high %sy usage due to which server is very slow. Below is strace count for syscall. What will be the reason for high %sy usage. % time seconds usecs/call ...
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37 views

Arch very long boot-time after kernel downgrade

I just downgraded my arch kernel from 4.x to 3.17.x for the sake of being able to use shared folders feature in vmware. Right now, everything is fine and it boots up too. But boot-time has greatly ...
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1answer
51 views

what does it mean 'fork()' will copy address space of original process

I'm studying 'operation system concepts' on my own and I'm studying the chp3. process part. There is an example where the 'fork()' function is called and depending of the returned pid value like the ...
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31 views

Minimum required packages for a LFS/DIY-Linux system?

I am trying to make a super-minimal linux system, as a base for experimentation, and just for the experience. I have built DIY Linux (similar to Linux from Scratch) before, but I was wondering how ...
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how to find which linux kernel commit made its way to exactly which kernel version [duplicate]

We have a problem that started appearing in kernel-uek-3.8.13-68.1.2.el6uek.x86_64. Symptoms and description matches exactly this linux kernel developers description ...
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29 views

Is there a way to expose extra settings through sysfs using the IIO framework?

The driver I'm developing has a number of settings I want the user to be able to change that don't really fit into the IIO framework. For example, using the IIO_CHAN_INFO_SAMP_FREQ enum in my read ...
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64 views

routing table “220” in Linux kernel 3.2.0-23-generic

I have a Linux machine with kernel 3.2.0-23-generic and it has rule with priority 220 in RPDB which points to routing table named "220": T42:~# ip rule show 0: from all lookup local 220: ...
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1answer
86 views

routing cache in latest Linux kernels

As I understand, routing cache was removed since Linux kernel 3.6. In systems with older Linux kernel one could view the content of the routing cache with ip route show cache command and routing ...
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When a process forks is its virtual or resident memory copied?

The standard way of making new processes in Linux is that the memory footprint of (parent) the parent process is copied and that becomes the environment of the child process until execv is called. ...
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68 views

how to increase Stack Size of a running program in C

I am trying to identify any way if we can increase the stack size of my running program after getting SIGSEGV. I know we can increase the size of stack by ulimit -c but, that did not solve this ...
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22 views

Why my limit on CPU does not validate via cgroups

/etc/cgconfig.conf ... group memlimit { memory { memory.limit_in_bytes = 8589934592; } } group cpulimit { cpu { cpu.shares = 1024; } } /etc/cgrules.conf: ...
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66 views

How to enable random PIDs on Linux?

I'm currently comparing random PID implementation on OpenBSD, FreeBSD and Linux from security perspective. As long as OpenBSD and FreeBSD are concerned, my work is done. However, while the answer ...
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314 views

Understand logging in Linux

As I understand, Linux kernel logs to /proc/kmsg file(mostly hardware-related messages) and /dev/log socket? Anywhere else? Are other applications also able to send messages to /proc/kmsg or /dev/log? ...
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60 views

Triggering hardware interrupts by connecting parallel port pins 9 and 10 does not work

I want to trigger hardware interrupts as described in the book Linux Device Drivers by connecting pins 9 and 10 with a wire. I tried that but apparently there's no interrupt beeing triggered: cat ...
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54 views

Linux doesn't drop FS Caches. Instead Memory starts Swapping

I'm quite confused about this behaviour of linux memory caching. total used free shared buffers cached Mem: 15953 14188 1765 64 ...
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195 views

Linux does not reply to ARP request messages if requested IP address is associated with another (disabled) interface

I have a PC(kernel 3.2.0-23-generic) which has 192.168.1.2/24 configured to eth0 interface and also uses 192.168.1.1 and 192.168.1.2 addresses for tun0 interface: root@T42:~# ip addr show 1: lo: ...
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100 views

How to create Linux Kernel Headers from Linux Kernel Source?

I'm working with Tiny Core Linux and attempting to install Vmware Tools, which of course needs the Kernel Headers :-). It does not appear they have the Kernel Headers readily available in a package, ...
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82 views

How to resolve dracut problem when intall Fedora 21

I'm Ubuntu User. But I wanted to change my OS from Ubuntu to Fedora. So I wanted to Fedora 21. But there is a problem. I'm using USB Drive to boot Fedora 21. When I try to install Fedora I get a ...
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181 views

What are the programs/commands which the magic SysRq key invoke?

From Magic SysRq key The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low level commands regardless of the system's state. It ...
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43 views

How SYN and ACK packets counted by the server(Linux)

I have a question about tcp layer of linux kernel. I want, Syn and ack packages received to server will be counted. where total_syn_count and total_ack_count are variables to be defined and will ...
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39 views

Do I have to publish kernel source if I release a custom kernel?

I have a kernel for an android phone ready for release. I always have the current source code already pushed to GitHub for release builds. However, I also have an experimental folder on my server ...
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70 views

SMB/CIFS mount not working with exec() call

To mount CIFS presently I use system() call in source, this works. If I try to run command manually on shell it works too. $ mount -t cifs //IP/dir /mnt -o user=name,pass=PASS,domain=mydomain,nounix ...
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76 views

Where is routing table stored internally in the Linux kernel?

When I execute route -n, from where exactly (from which structs) is the information displayed retrieved? I tried executing strace route -n but I didn't help me finding the right place it's stored.
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57 views

RHEL not booting with the updated kernel after upgrade [closed]

We have recently upgraded RHEL boxes, but the system only booted with the old kernel. Observation is that there is no link /etc/grub.conf to /boot/grub/grub.conf. Now, to boot the system with the new ...
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96 views

how to untar file in linux red hat?

I am compiling linux red hat stable kernel on red hat linux and the error which I am facing is as below
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Which linux kernel options need to be enabled to support bluetooth low energy?

Which are the mandatory and optional options?
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37 views

Kernel modules for compiled kernel

I cannot find kernel-headers. For the first time I compiled and installed the latest kernel (4.0.3) on my Debian Wheezy, and now I am trying to install ndiswrapper using module assistant. For that, ...
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Trying to use KDBG, but it produces error 11

I am trying to start kdbg on Ubuntu, but it produces this error message: MNG error 11: function is invalid at this point ; chunk MHDR; subcode 0:0 MNG error 11: function is invalid at this point ; ...
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85 views

How to read the output of the show-memory-usage SysRq?

I couldn’t find any (recent) documentation on reading the output of the show-memory-usage SysRq (Alt+SysRq+m). So what can one learn from looking at it? Here is an example output form my box (Kernel ...
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how to check a kernel version which was used when building package

I use apt when downloading packages from Ubuntu repositories. How can I check which kernel version was used when building package? When it is important (kernel version of the build server vs. kernel ...
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103 views

What is the difference between Local timer interrupts and the timer?

When I do cat /proc/interrupts on my multicore x86_64 desktop PC (kernel 3.16) I see this: 0: 16 0 IO-APIC-edge timer LOC: 529283 401319 Local timer interrupts ...
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1answer
160 views

Change hidraw device from mouse to joystick

I have a wireless PS3 controller adapter that is plugged in to my Ubuntu 14.04 box. It has 2 modes: XInput and DInput, which as far as I can tell, it just passes two different vendor/product id's ...
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63 views

How to get the mouse/keyboard raw events?

I want to intercept the raw events from the keyboard (or the mouse, eventually). I tried to use the /dev/input/[...] files, they are very practical and I can read the events of any key even caps lock ...
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Want a bash script for file system monitoring for multiple RHEL servers [duplicate]

I'm trying to prepare a bash script to monitor file system utilization for more than 80% on 20 RHEL 6 servers. Below is the script, #!/bin/bash ADMIN="abcd@zxy.com" ALERT=80 dt=`date '+%a %b %e %I:%M ...
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0answers
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How to work with a kernel one has no information about?

I'm working with a system to automatically assemble Live CDs. It came packaged with a kernel (seemingly based on 3.13.11), that has been working without problems so far. I noticed that, when I try ...
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Having problems with negative monitor channel, intimidated!

When I try this command: aireplay-ng -1 0 mon0 -a xx:xx:xx:xx:xx:xx I get this output: No source MAC (-h) specified. Using the device MAC (xx:xx:xx:xx:xx:xx) 17:51:23 Waiting for beacon frame ...