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

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Understanding the Linux kernel source

I am trying to understand how a function, say mkdir, works by looking at the kernel source. This is an attempt to understand the kernel internals and navigate between various functions. I know mkdir ...
101
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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 ...
71
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5answers
14k views

Why isn't Linux embraced as the official GNU kernel?

While I knew for quite some time the existence of Hurd, and its mission as the official GNU Operating System kernel, I was wondering how come Linux is not embraced as the official GNU kernel over the ...
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3answers
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Does the kernel have a main() function? [closed]

I am learning device drivers and Kernel programming. According to Jonathan Corbet's book, there is no main() function in device drivers. So I two questions: Why don't we need a main() function in ...
28
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7answers
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Why does mount require root privileges?

Why does Linux require that a user be root/using sudo/specifically authorized per mount in order to mount something? It seems like the decision as to whether to allow a user to mount something should ...
24
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1answer
546 views

What would be the best way to work around this glibc problem?

I administer a Gentoo Hardened box that uses file capabilities to eliminate most of the need for setuid-root binaries (e.g. /bin/ping has CAP_NET_RAW, etc). Infact, the only binary I have left is ...
23
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7answers
13k views

Linux Kernel: Good beginners' tutorial

I'm interested in modifying the kernel internals, applying patches, handling device drivers and modules, for my own personal fun. Is there a comprehensive resource for kernel hacking, intended for ...
23
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1answer
2k views

High CPU usage with CFS?

I asked a previous question to try and isolate the source of an increase in CPU usage when moving an application from RHEL 5 to RHEL 6. The analysis that I did for that seems to indicate that it is ...
20
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1answer
446 views

How to get started writing drivers?

I have a throw-away cheap laptop I'd like to twiddle around, a Thinkpad SL 500. What bothers me are two leds, the one for wireless connectivity, and the one for hibernation, which don't light up at ...
14
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2answers
1k views

The UEFI & SecureBoot impact, how severe?

I'm planning to buy a new laptop in the coming days, and I'm quite impressed with new, cool Ultrabooks. As a long-time GNU/Linux user, I'll of course install a distro of my choice on it. Chances are ...
13
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5answers
2k views

Can ps display only non kernel processes on Linux?

How can I ask ps to display only user processes and not kernel threads? See this question to see what I mean...
13
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3answers
9k views

Linux: How to find the device driver used for a device?

If my target has one device connected and many drivers for that device loaded, how can I understand what device is using which driver?
12
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3answers
2k views

Why there are many BSD systems but only one Linux kernel?

Why there are many BSD systems but only one Linux kernel? I wonder why BSD was forked many times, but no such thing with Linux.
12
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4answers
675 views

Linux on a 286?

I don't own a 286 nor do I intend to run Linux on one. However since the 286 has protected mode, why is it frequently stated that Linux requires a 386 CPU or higher? From ...
11
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2answers
3k views

Does Android really use the same kernel as Linux?

I read from somewhere that Android uses the Linux Kernel. Is it really true? I thought the Linux Kernel was meant for desktop operating systems.
11
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2answers
1k views

How many actual developers work on the Linux Kernel

For a study I am doing I was asked how many actual developers commit on a typical kernel version. I know there is Linus Torvalds as the main developer, followed by many second main developers. ...
11
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3answers
662 views

How to tell Linux Kernel > 3.0 to completely ignore a failing disk?

I am asking this question here in the hope that some Linux-kernel guru can have an answer. This question has been asked on AskUbuntu and on SuperUser without answers: thinking better, it is really ...
11
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1answer
2k views

What happens in each step of the Linux kernel-building process?

I've read many tutorials about how to build custom kernels and boot Ubuntu using those kernels, and successfully followed the guides and booted custom kernels, but I have no understanding about what ...
11
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3answers
1k views

Given a git patch id, how to find out which kernel release contains it?

Assume I have some issue that was fixed by a recent patch to the official Linux git repository. I have a work around, but I’d like to undo it when a release happens that contains my the fix. I know ...
10
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2answers
498 views

Observing a hard-disk write in kernel space (with drivers/modules)

Apologies in advance if this post is a bit dense/messy, but I'm having a hard time formulating it better... Basically, I would like to study what happens upon a hard disk write, and I'd like to know: ...
10
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3answers
2k views

Can I create a virtual ethernet interface named eth0?

This is a rather odd question, because normally it would not make sense to do that. I am running Arch based on the Linux 3.10.5-1 kernel. The system uses the new de-facto naming conventions of ...
9
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3answers
240 views

kernel: Namespaces support

I am wondering what exactly the “Namespaces support” feature in the Linux kernel means. I am using kernel 3.11.1 (the newest stable kernel at this time). If I decide to disable it, will I notice any ...
8
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2answers
254 views

Why does the Linux kernel report “out of disk space” when in reality it is out of i-nodes

A friend of mine who likes programming in the Linux environment, but doesn't know much about the administration of Linux recently ran into a problem where his OS (Ubuntu) was reporting "out of disk ...
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2answers
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How to boot EFI kernel using QEMU (kvm)?

Hey guys I'm trying to emulate a EFI enviroment using QEMU (kmv), virtualbox takes 15 minutes to boot in EFI mode using archboot. Using legacy BIOS mode I can boot using this command: ...
8
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2answers
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minimal TCP MSS in Linux

The TCP MSS in Linux must be at least 88 (include/net/tcp.h): /* Minimal accepted MSS. It is (60+60+8) - (20+20). */ #define TCP_MIN_MSS 88U My question is: where did they come up with ...
8
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2answers
83 views

How does the system shutdown of a linux kernel work internally?

I have somehow an rough idea of how the userspace and init-system (be it classic init sysV /upstart/ systemd) work at system shutdown. (Essentially there is an order succession of "Stop!", "Please ...
8
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2answers
113 views

How should I solicit feedback from a tree maintainer for patches sent to the lkml?

I have submitted a patch to the linux kernel that has gotten several reviews and gone through a couple iterations on the mailing list. It has been ACKed and reviewed by two developers, but they say ...
8
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1answer
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Isolating cause of higher CPU usage on RHEL 6 vs RHEL 5

I'm currently looking to move our system from RHEL 5 to RHEL 6, but I've run into a snag with unexpectedly high CPU usage on the RHEL 6 machines. It appears that this may be due at least in some part ...
7
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1answer
5k views

How to display kernel command line parameters?

In the grub.conf configuration file I can specify command line parameters that the kernel will use, i.e.: kernel /boot/kernel-3-2-1-gentoo root=/dev/sda1 vga=791 After booting a given kernel, is ...
7
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2answers
386 views

How exactly does printk work internally?

I know printf needs help from the OS to do its job. I also know printf does not work in the Linux source code as there is no library. And so we have printk for debugging. How does printk work ...
7
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2answers
201 views

Strange temporary network outage in Linux

I'm facing a very annoying problem that I noticed a week from now and for which I can't find an answer: my network suddenly stops responding, usually coming back exactly 25 seconds later. I was using ...
7
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2answers
132 views

Why should I build a custom kernel? [closed]

Several of my coworkers have been building custom kernels for their workstations and servers. What advantages/disadvantages are there to building a custom kernel? Why should I build a custom kernel? ...
7
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3answers
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mptscsih: ioc0: task abort: SUCCESS (rv=2002) causes 30 seconds freezing

I/O to my software RAID6 often freezes for around 30 seconds after which everything is back to normal. After the freeze is over this is put into syslog: Mar 14 18:43:57 server kernel: [35649.816060] ...
7
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1answer
295 views

How is nice working?

sched_setscheduler says : All scheduling is preemptive: if a process with a higher static priority becomes ready to run, the currently running process will be preempted and ...
7
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2answers
2k views

What is the appropriate value of vm.swappiness when using zram?

I'm using zram on my computer as a compressed RAM-backed swap. When the system needs to swap something out, swapping it to a zram-backed swap file is more or less equivalent to compressing that data ...
7
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2answers
224 views

Linux /proc/sys/kernel: where are the files sysrq-sticky, sysrq-key, and sysrq-timer?

Documentation for Red Hat Enterprise Linux 3 (section 5.3.9.3) mentions these files in /proc/sys/kernel/: sysrq sysrq-key sysrq-sticky sysrq-timer The documentation for RHEL 5 also mentions them. ...
7
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1answer
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Enabling IOMMU in the kernel for graphics card pass-through

Short question: How can I turn on the intel_iommu setting in the Linux kernel? I run a Debian host, using the grub2 bootloader. Documentation I've seen says to edit /boot/grub/menu.lst, which seems ...
6
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1answer
118 views

show parameters of running kernel

I would like to see with what parameters the running kernel has been started. i.e., I mean those parameters that are specified with the append option, such as ipv6.disable=1 or rootfstype=ext2 Is ...
6
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1answer
2k views

Load Linux bzImage in QEMU?

I compiled a Linux by doing make menuconfig then make and now I have compiled the most recent version of Linux. How can I load the kernel into QEMU?
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2answers
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An oom killer thats baffling me

I am not able to understand why would kernel issue this oom killer when I see enough memory is available: Also why are there so many kernel cache pages allocated? I say enough memory is available ...
6
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4answers
888 views

Difference between bootable and non-bootable partitions

What is the difference between a bootable and non-bootable partition? I know that a user cannot boot a system from a partition marked non-bootable and can from one marked bootable. I want to know ...
6
votes
2answers
8k views

Where is the struct task_struct definition in the 2.6.30.5 Linux Kernel?

In the version 2.6.15 kernel, I got that I can rewrite the task_struct in the file (include/linux/sched.h),like: struct task_struct { unsigned did_exec:1; pid_t pid; pid_t tgid; ...
6
votes
2answers
76 views

Location of the kernel binary (when not in /boot)?

I failed to find the kernel binary in the standard location in /boot. I've also searched the whole file system for vmlinux or bzimage find / -iname vmlin* find / -iname bzimage However, this is an ...
6
votes
1answer
956 views

How to debug system freeze?

I'm experiencing strange bug when I close lid of my laptop - system freezes (no reaction on keys, no response form ssh) hard and displays some strange colour effects. The kernel log (after reboot) ...
6
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0answers
216 views

Allocated Memory difference in xen guests after using Linux 3+ kernel [closed]

Can someone explain to me why there is a memory difference in Guests with the same configuration? Hypervisor: xen 4.2 64 bit VM1: Centos 5.7 with 2.6.18-274.el5xen Assigned memory from xen is ...
5
votes
1answer
114 views

Linux: What is a tainted kernel?

Under certain conditions, the Linux kernel may become tainted. For example, loading a proprietary video driver into the kernel taints the kernel. This condition may be visible in system logs, kernel ...
5
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1answer
3k views

Why does Linux show both more and less memory than I physically have installed?

I know about swap - this question isn't about that. In dmesg, the Linux (x86-64) kernel tells me this about how much memory I have: [ 0.000000] Memory: 3890880k/4915200k available (6073k kernel ...
5
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4answers
2k views

Are FIFO, pipe & Unix domain socket the same thing in Linux kernel?

I heard that FIFOs are named pipes. And they have exactly the same semantics. On the other hand, I think Unix domain socket is quite similar to pipe (although I've never made use of it). So I wonder ...
5
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1answer
422 views

What are the main differences between Unix and Linux kernels today?

I know that many of the same programs run flawlessly on top of both kernels. I know that historically, the two kernels came from different origins. I know philosophically too that they stood for ...
5
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2answers
2k views

How to set OOM killer adjustments for daemons permanently?

Running some Linux servers with single or just a few vital system service daemons, I would like to adjust the OOM killer for those daemonized processes in case something odd happens. For example, ...