KernelTrap - Kernel

syscall interception module on 2.6.32

saliari2 — Sat, 08 May 2010 14:00:15 +0000

Hi,

I am using the following kernel module to intercept some syscalls. I have got sys_call_table address from the /boot/System.map.x.x. The module works file on Ubuntu 7.10 (2.6.24) but gets killed upon insmod in Ubuntu 10.04 and Fedora 12 (2.6.32) with error "Kernel paging request error address c0xxxxx [which is, based on System.map, an address in sys_call_table]".

How to determine Amount of free kernel memory and problem with __get_free_pages()

Wed, 05 May 2010 03:41:06 +0000

I want to write a loop that sucks up all the 2mb slugs of memory I can get in the kernel. However, I want to leave "some" free space (say 20% of the machine's total phys mem). So, how can I do that? I have a loop now something like as an experiment to get all the mem I can and then release enough for the system to continue running but the kernel hangs:

for( i = 0; i < MAX_SLUGS; ++i )
{

NFS mount failure

Mon, 02 Nov 2009 18:53:54 +0000

I have a problem I'm hoping someone can help me with...

I have an NFS server/client setup. On the server side, I export a romfs filesystem to the NFS. The client computers boot via PXE bootloader and mount their root filesystem via NFS, using tempfs/unionfs to make parts of the filesystem read/write (i.e., /etc, /var, etc)

Dealing with Linux kernel configuration's diffs

Dmitry Shurupov — Fri, 11 Sep 2009 16:22:31 +0000

We're using a lot of different kernel configurations on our servers running Gentoo Linux and Linux VServer. Kernels' configs depend on hardware and functions of every server. Every time new kernel is released and/or we need to enable/disable some features for all servers' kernels we have to update .config's manually.

mtrr: type mismatch on starting X server

kushalkoolwal — Thu, 23 Jul 2009 23:00:07 +0000

I am using Debian Lenny with 2.6.30 kernel on my Intel Atom Poulsbo chipset computer and I get the following messages in my dmesg when I start the X server:

[ 22.760737] mtrr: type mismatch for 3ffc0000,10000 old: write-back new: write-combining [ 22.760805] mtrr: type mismatch for 3ff80000,40000 old: write-back new: write-combining

High Idle Load Average

Jeremy — Sat, 06 Oct 2007 18:59:52 +0000

When a Linux user reported a repeatedly high load average on an idle server, tracking the problem to a specific patch labeled, "user of the jiffies rounding code", Andrew Morton replied, "this is unexpected. High load average is due to either a task chewing a lot of CPU time or a task stuck in uninterruptible sleep." Linus Torvalds disagreed, explaining:

"We saw high loadaverages with the timer bogosity with 'gettimeofday()' and 'select()' not agreeing, so they would do things like 'date = time(..); select(.. , timeout = );' and when 'date' wasn't taking the jiffies offset into account, and thus mixing these kinds of different time sources, the select ended up returning immediately because they effectively used different clocks, and suddenly we had some applications chewing up 30% CPU time, because they were in a loop that *tried* to sleep."

Linus offered what he described as an "idiotic patch" to cause the load average to not be calculated exactly once every 5 seconds to prevent it from being in sync with something else waking up every 5 seconds, noting, "the load average is not calculated every tick, because that's not just expensive, but we also want to have some time-based decay." Arjan van de Ven pointed out that this shouldn't help, "I mean, the load gets only updated in actual timer interrupts... and on a tickless system there's very few of those around..... and usually at places round_jiffies() already put a timer on." Linus agreed with this reasoning, suggesting, "maybe Anders' problem stems partly from the fact that he really is using the tweaks to make that tickless theory more true than it tends to be on most systems?" Arjan pointed out that a lot of work has been successful in making tickless kernels wake up less, "we fixed a TON of stuff over the last months.. standard desktops (F8 / next Ubuntu) will be around 10 wakeups/sec, in a lab environment you can get below 2 ;)"

Error during installation

mayank.jarsaniya — Fri, 13 Jul 2007 04:56:14 +0000

when installing linux error shows:
append a correct "root" boot option
kernel panic: VFS: Unable to mount root fs on 48:05

Details:
i am using windows XP on NTFS partition on core dual with sata harddisk of ATAPI...
And want to install Linux redhat 9 on same working environment.

Please help to solve the error.