Everything about UNIX kernels: development, configuration, compilation, design, etc.
225
votes
7answers
19k views
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 ...
53
votes
12answers
4k views
What is the benefit of compiling your own linux kernel?
What benefit could I see by compiling a Linux kernel myself? Is there some efficiency you could create by customizing it to your hardware?
38
votes
3answers
16k views
How do I read from /proc/$pid/mem under Linux?
The Linux proc(5) man page tells me that /proc/$pid/mem “can be used to access the pages of a process's memory”. But a straightforward attempt to use it only gives me
$ cat /proc/$$/mem ...
36
votes
5answers
12k 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?
24
votes
12answers
2k views
How can I tweak my Linux desktop to be more responsive?
I have the experience that Linux works fine until the physical memory is exhausted. As soon as swap space is used the performance is severely degraded and the GUI becomes unresponsive.
This problem ...
22
votes
1answer
1k 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 ...
18
votes
7answers
9k 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 ...
18
votes
1answer
372 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 ...
17
votes
3answers
3k views
Who's consuming my inotify resources?
After a recent upgrade to Fedora 15, I'm finding that a number of tools are failing with errors along the lines of:
tail: inotify resources exhausted
tail: inotify cannot be used, reverting to ...
17
votes
3answers
2k views
What is the difference between reboot , init 6 and shutdown -r now?
I just want to know difference between in
reboot
init 6
shutdown -r now
and which is the safest and the best?
16
votes
1answer
5k views
How to assign USB driver to device
This question is two-fold:
First, how do you manually detach a driver from a USB device and attach a different one? For example, I have a device that when connected automatically uses the ...
15
votes
2answers
532 views
Linux kernel for Nintendo Wii
I'm trying to compile a Linux kernel for the Nintendo Wii newer than the version 2.6.32 with mike p5 patches, which I have been using since now without problems. Since version 2.6.33 Wii support is ...
14
votes
1answer
434 views
How is new hardware support added to the linux kernel?
Imagine there's a company A that releases a new graphics adapter. Who manages the process that results in this new graphics adapter being supported by the Linux kernel in the future? How does that ...
14
votes
4answers
1k views
Kernel Hacking Environment
I have been working in embedded OS like uCOS, ThreadX. While I have coded apps in Linux, now I’m planning to start learning Linux Kernel. I have few questions regarding the environment.
Which is ...
14
votes
2answers
5k views
how to check rx ring, max_backlog, and max_syn_backlog size
Quite often in the course of troubleshooting and tuning things I find myself thinking about the following Linux kernel settings:
net.core.netdev_max_backlog
net.ipv4.tcp_max_syn_backlog
...
13
votes
4answers
563 views
What is new in Kernel 3.0?
I understand this is somewhat less Ubuntu related, but it affects it.
So,what is so new about it that Linus decided to name it 3.0? I'm not trying to get information about the drivers that got into ...
13
votes
5answers
1k views
Any way to restart a Linux machine via SSH if the root filesystem is not working?
Just as a curiosity; something went wrong with a Linux machine, making the root file system show up as "64Z". A few commands work, like top, df, and kill, but others like reboot come up with "command ...
13
votes
3answers
863 views
Why don't you need to update drivers? (Or do you?)
In my life I've not once updated drivers on any of my Linux systems, though they have all been desktops. A friend was asking me why one does not need to update Linux drivers and I found myself unable ...
13
votes
4answers
368 views
How do I learn what I can do with /proc and /sys
I'd like to know more about the advanced uses of the /proc and /sys virtual filesystems, but I don't know where to begin. Can anyone suggest any good sources to learn from? Also, since I think sys has ...
13
votes
4answers
2k views
What is the difference between kernel drivers and kernel modules?
When I do a lspci -k on my Kubuntu with a 3.2.0-29-generic kernel I can see something like this:
01:00.0 VGA compatible controller: NVIDIA Corporation G86 [Quadro NVS 290] (rev a1)
Subsystem: ...
13
votes
1answer
4k views
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 ...
13
votes
1answer
1k views
Why isn't a straightforward 1/5/15 minute moving average used in Linux load calculation?
Until recently i thought the load average (as shown for example in top) was a moving average on the n last values of the number of process in state "runnable" or "running". And n would have been ...
13
votes
2answers
3k views
Why does high disk I/O reduce system responsiveness/performance?
I never quite understood why high disk I/O slowed the system so much. It's strange to me because I would expect the slow-down to affect only those processes dependent on the hard/optical drive data, ...
12
votes
3answers
3k views
How can I reserve a block of memory from the Linux kernel?
I have a device that needs a block of memory that is reserved solely for it, without the OS intervening. Is there any way to tell BIOS or the OS that a block of memory is reserved, and it must not ...
12
votes
4answers
2k views
Read the stack of another process?
I'm trying to read a child process's stack but with no luck.
I know it is possible using ptrace, but ptrace's interface allows you to read only one word at a time, and I'm trying to scan a larger ...
11
votes
3answers
7k views
How to reload udev rules without reboot?
How should one reload udev rules, so that newly created one can function?
I'm running Arch Linux, and I don't have a udevstart command here.
Also checked /etc/rc.d, no udev service there.
11
votes
1answer
12k views
How is a message queue implemented in the Linux kernel?
I would like to know how Message Queues are implemented in the Linux Kernel.
11
votes
1answer
634 views
Rebooting without shutting off?
I have been using Linux Mint Debian with Debian unstable and noticed that when I press restart, instead of going all the way back to the BIOS, then grub, then booting up, I seem to be shutting down ...
11
votes
3answers
1k views
Increasing kernel memory size
I have an embedded board with 512MB of RAM running Linux 2.6.29 and UBoot bootloader. But the kernel is able to utilize only 128MB of RAM.
I tried changing the value of XCODE_MEMSIZE, which I think ...
10
votes
6answers
2k views
How does Linux kernel compare to microkernel architectures?
I read once that one advantage of a microkernel architecture is that you can stop/start essential services like networking and filesystems, without needing to restart the whole system. But considering ...
10
votes
2answers
430 views
Contents of /proc
Is there a site someplace that lists the contents of /proc and what each entry means?
10
votes
1answer
149 views
Can entropy consumption at program start be prevented?
I use Knoppix (or other Live CDs/DVDs) as a secure environment for creating valuable crypto keys. Unfortunately entropy is a limited resource in such environments. I just noticed that each program ...
9
votes
5answers
3k views
Compiling GNU/Linux with -O3 optimization
It's said that compiling GNU tools and Linux kernel with -O3 gcc optimization option will produce weird and funky bugs. Is it true? Has anyone tried it or is it just a hoax?
9
votes
3answers
2k views
How do I begin with building a Linux system from scratch?
I tried to make an operating system with my on custom built kernel. It didn't work out too well. I am using Ubuntu and have downloaded Linux 3.2.7 from kernel.org . I am not trying to change the ...
9
votes
3answers
8k views
How is an Interrupt handled in Linux?
I just know that Interrupt is a hardware signal assertion caused in a processor pin. But I would like to know how Linux OS handles it.
What all are the things that happen when an interrupt occurs?
9
votes
1answer
3k views
How can I configure cgroups to fairly share resources between users?
There used to be a kernel config option called sched_user or similar under cgroups. This allowed (to my knowledge) all users to fairly share system resources. In 2.6.35 it is not available. Is there a ...
9
votes
1answer
2k views
What does the Virtual kernel Memory Layout in dmesg imply?
While going through the "Output of dmesg" I could see a list of values which i am not able to understand properly.
Memory: 2047804k/2086248k available (3179k kernel code, 37232k reserved, 1935k ...
9
votes
1answer
6k views
How to use Linux kernel driver bind/unbind interface for USB-HID devices?
First background. I am developing a driver for Logitech game-panel devices. It's a keyboard with a screen on it. The driver is working nicely but by default the device is handled by HID. In order to ...
9
votes
2answers
275 views
How am I supposed to keep up with kernels as a developer?
I'm developing for a specific TI ARM processor with custom drivers that made it to the kernel. I'm trying to migrate from 2.6.32 to 2.6.37, but the structure changed so much I will have weeks of work ...
9
votes
2answers
553 views
Is there a downside to ksplice?
ksplice is an open source extension of the Linux kernel which allows system administrators to apply security patches to a running kernel without having to reboot the operating system. (From ...
9
votes
3answers
228 views
Where to find explanation of kernel processes?
I want to know about kernel processes, like [migration], [kswapd], etc. Where are kernel processes like these documented?
9
votes
2answers
2k views
How to set a video mode in linux with kms/drm?
How can I set the video mode in Linux the low level way? As far as I know the lowest layer in userspace would be to request KMS via DRM. Is this correct? And if so, how could I achieve a mode switch ...
9
votes
2answers
579 views
Install new kernel in PowerPC debian
I compiled a new kernel image on x86 using cross compiler with these commands (source):
$ cp arch/powerpc/configs/pmac32_defconfig .config
$ make ARCH=powerpc menuconfig
$ make ARCH=powerpc ...
8
votes
6answers
1k views
How to find information about the system/machine in Unix?
I have always found it difficult to find information about the system itself in Unix, whether it be
Which OS I am using (version number and all, to compare it with the latest available builds)?
...
8
votes
2answers
2k views
Why are the grsecurity patches not included in the Vanilla Kernel?
What are the reasons that grsecurity patches (or the security features it brings) are not included in the kernel by default. When looking at the benefits for security it seems the vanilla kernel is ...
8
votes
2answers
1k views
Heavy write activity on SSD nukes system performance
I've noticed that when I do heavy write applications, the whole system slows down. To test this further I ran this to do a (relatively) low-CPU, high disk activity:
john -incremental > file_on_SSD
...
8
votes
1answer
844 views
What's the progress regarding improving system performance/responsiveness during high disk I/O?
Whenever there is high disk I/O, the system tends to be much slower and less responsive than usual. What's the progress on Linux kernel regarding this? Is this problem actively being worked on?
8
votes
3answers
9k views
what is the difference between spin locks and semaphores?
What are the basic differences between spin locks and semaphores in action?
8
votes
4answers
3k views
Use of O_DIRECT on Linux
If this question is too programmer oriented, let me know. I wonder if there are people familiar with the O_DIRECT flag for the open() system call on Linux 2.6? Linus disparages its use, however high ...
8
votes
4answers
905 views
GRUB on USB Drive — adding OSes
Some Background:
Coming from a largely Windows background (though I'm familiar with Ubuntu, etc.) and using a Windows 7 machine to complete this task
Have gotten GRUB installed successfully to the ...
