In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources (the communication between hardware and software ...
42
votes
21answers
11k views
rm on a directory with millions of files
Background: physical server, about two years old, 7200-RPM SATA drives connected to a 3Ware RAID card, ext3 FS mounted noatime and data=ordered, not under crazy load, kernel 2.6.18-92.1.22.el5, uptime ...
18
votes
3answers
13k views
Turn off the Linux OOM killer by default?
The OOM killer on Linux wreaks havoc with various applications every so often, and it appears that not much is really done on the kernel development side to improve this. Would it not be better, as a ...
16
votes
2answers
944 views
What is the largest hardware clock update the Linux kernel “11-minute mode” can make?
When certain time-related programs (like ntpd) are running on a Linux system, the kernel will switch into so-called "eleven minute mode" (see the hwclock man page) whereby it will automatically update ...
13
votes
5answers
1k views
is ksplice production ready?
I would be interested to hear the serverfault community's experiences with Ksplice in production.
Quick blurb from wikipedia:
Ksplice is a free and open source extension of the Linux kernel ...
13
votes
3answers
17k views
Improving TCP performance over a gigabit network with lots of connections and high traffic of small packets
I’m trying to improve my TCP throughput over a “gigabit network with lots of connections and high traffic of small packets”. My server OS is Ubuntu 11.10 Server 64bit.
There are about 50.000 (and ...
12
votes
3answers
41k views
“Possible SYN flooding” in log despite low number of SYN_RECV connections
Recently we had an apache server which was responding very slowly due to SYN flooding. The workaround for this was to enable tcp_syncookies (net.ipv4.tcp_syncookies=1 in /etc/sysctl.conf).
I posted a ...
12
votes
4answers
10k views
How do I list loaded Linux module parameter values?
Is there a standard way to list the parameter values of a loaded Linux module? I'm essentially probing for another answer to this Linux kernel module parameters question, because the module I'm ...
12
votes
2answers
3k views
Strange: why does linux respond to ping with ARP request after last ping reply?
I (and a colleague) have just noticed, and tested, that when a Linux machine is pinged, after the last ping it initiates a unicast ARP request to the machine that initiated the ICMP ping. When pinging ...
8
votes
8answers
2k views
Rebooting servers for kernel updates
I have a few production Fedora and Debian webservers that host our sites as well as user shell accounts (used for git vcs work, some screen+irssi sessions, etc).
Occasionally a new kernel update will ...
8
votes
4answers
489 views
How can I troubleshoot high Kernel time?
I have unusually high Kernel time on my CPUs as shown in task manager.
What are some ways I can troubleshoot this?
8
votes
4answers
18k views
How to fix “BUG: soft lockup - CPU#0 stuck for 17163091968s”?
UPDATE: I updated the title of the message, because I've recently seen more of these problems with this exact time amount of 17163091968s. This should help people investigating the symptoms to find ...
8
votes
2answers
539 views
Linux Kernel Versioning: Debian Sid vs Ubuntu Precise
I have setup two machines:
On one machine I have installed Ubuntu Precise 12.04 beta and dist-upgraded to the latest packages.
On the other machine I have installed Debian Sid Unstable and ...
7
votes
2answers
269 views
/dev/shm & /proc hardening
I've seen mention of securing /dev/shm and /proc and I was wondering how you do that and what it consists of doing? I assume this involves /etc/sysctl.conf editing of some kind right.
Like these?
...
6
votes
6answers
361 views
How to Minimize Linux Server Reboots
Last week there were a fair few comments on a slashdot article about whether Unix (or Linux) machines ever need to be rebooted. More than a few of the commenters mentioned having machines with ...
6
votes
2answers
1k views
How can I take advantage of IW10 in kernel 2.6.33?
I've read that 2.6.33+ allows setting custom cwnd.
if the IW is 10 by default (for all distros? only some?)
how does one view what the current IW is on a particular compiled kernel?
references:
...
6
votes
2answers
423 views
Kernel updates without rebooting
Similar to some of the topics touched on in this question, Rebooting servers for kernel updates, I was curious if there was a way in which one could apply kernel updates to the system without ...
6
votes
2answers
827 views
TCP SYN Flooding Detection Method in the Linux Kernel
When the Linux kernel detects SYN Flooding it logs a message like:
possible SYN flooding on port 80. Sending cookies
Does anyone know the exact method that the kernel uses to detect this?
5
votes
2answers
7k views
Damaged /vmlinuz and /initrd.img symbolic links after Kernel uninstall
OS: Ubuntu 8.04 LTS Server Edition
We just rolled back an kernel update using the following command:
sudo apt-get remove linux-image-2.6.24-24-server
The uninstallation was successful, but it had ...
5
votes
4answers
1k views
The Gentoo live-cd shows my drives as “hda”, but booting into my own kernel shows “sda” (therefore, boot fails). What should I do?
The Gentoo live-cd shows my drives as "hda", so I followed the Gentoo handbook and configured my partitions as "hda". However, the boot failed because, when booting into my kernel, it wanted to refer ...
5
votes
2answers
6k views
Can I increase inode count in Linux?
Sorry for my poor English.
I have a Linux MIPS router with 2.4.17 kernel.
Root fs is a tmpfs and /rom is a cramfs. There is 4MB free memory and 3MB free on tmpfs.
I can create a few new empty ...
5
votes
3answers
4k views
How does Linux determine the SCSI address of a disk?
Greetings,
I'm working with RHEL 5.5 guest VMs under VMware ESX 4. When I configure the virtual disks in the VM hardware settings, each disk has a SCSI address in the format "N:M". For example, "1:3" ...
5
votes
1answer
5k views
How do ulimit -n and /proc/sys/fs/file-max differ?
I notice that on a new CentOS image that I just booted up off of EC2 that the ulimit default is 1024 open files, but /proc/sys/fs/file-max is set at 761,408 and I'm wondering how these two limits work ...
5
votes
3answers
8k views
Soft limit vs Hard limit?
Can anyone explain in layman's terms what the difference between soft and hard limit is?
Should I set my soft and hard limit to be the same? Or should soft be significantly lower? Does the system ...
5
votes
2answers
2k views
Converting an EC2 AMI to vmdk image
I've come quite close to getting Amazon Linux to boot inside VirtualBox, thanks to this answer and these websites. A quick overview of the steps I've taken:
Launch EC2 instance with Amazon Linux ...
5
votes
2answers
525 views
Monolithic vs Micro kernel
What are the differences between a monolithic kernel and a microkernel with respect to structure and security. My friend told me that Linux systems have monolithic kernel and thus are not easier to ...
5
votes
1answer
1k views
Why won't FreeBSD reboot after a kernel crash?
Once in a while I get my server running FreeBSD 8.0 amd64 fail due to bad memory (incompatible with motherboard) modules. Each time it happens, the box stalls with the last note saying that it will ...
4
votes
2answers
8k views
How do I upgrade the kernel in Ubuntu Server 10.04?
I'm running Ubuntu Server 10.04 LTS. When I login I see the message:
39 packages can be updated.
18 updates are security updates.
The usual formula of
sudo apt-get update
sudo apt-get upgrade
...
4
votes
1answer
90 views
What happens if a linux kernel argument is passed twice with different values?
As the question states, what if I pass
kernel /vmlinuz audit=1 audit=0
Will auditing enabled or disabled? Or will the kernel just freak out? Or is it undefined and will depend on the build of the ...
4
votes
1answer
93 views
Linux: Visualize writes to a file
I am looking for a way to visualize writes to a big file (2GB) in real-time. The writing process isn't just appending data to the end of the file. Instead, it acts like a container or like a block ...
4
votes
3answers
3k views
Kernel Log “TCP: Treason uncloaked!”
On one linux server (Gentoo hardened), we are experiencing bursts of the following messages in dmesg from time to time:
TCP: Treason uncloaked! Peer xx.xx.xxx.xxx:65039/80 shrinks window ...
4
votes
3answers
3k views
Interpreting cryptic kernel “page allocation failure” messages
I have a multi-user CentOS 6.1 database system running an application named ABC. The server is 64-bit, 8GB RAM and 6 vCPU (on VMWare ESXi 4). We get frequent dumps into the dmesg and the system logs ...
4
votes
7answers
1k views
Linux freezes every few seconds
We're having an issue where one our Linux boxes (Ubuntu 10.04 LTS, running on EC2 with a quadruple-large size, 68GB of RAM and 8 virtual cores with 3.25GHz each) freezes up every few seconds. Typing ...
4
votes
3answers
2k views
How can I find out what is causing interrupts on Windows?
Occasionally I come across servers (Windows 2003 and 2008) with high processor % interrupt time. Is there a way to see what program or device is causing the interrupts?
4
votes
3answers
292 views
Compiling kernel version >= 2.6.34 on CentOS 5: RAID set “ddf1_foo” was not activated?
I want to mount a Ceph FS on some CentOS 5 servers. Since the ceph-fuse failed with below errors:
# ceph-fuse --no-fuse-big-writes -m 192.168.2.15:6789 /mnt/ceph/
ceph-fuse[7528]: starting ceph ...
4
votes
1answer
226 views
Disabling/Enabling Modules Parameter RHEL
I'm working with kernel module parameters, and I've found myself a bit confused.
In particular, I'm attempting to enable posix ACL support for XFS file systems. This requires the XFS module to be ...
4
votes
1answer
206 views
BSD 50% interrupt utilization in irq0/clock
On OpenBSD on an Atom 450, with HPET configured in the BIOS and not, also with Hyperthreading/ACPI on-off, nothing seems to make a difference.
Here's my vmstat -iz
# vmstat 2
procs memory ...
4
votes
2answers
301 views
What are the mandatory Linux kernel modules to run inside of ESXi
I'm used to rolling my own kernels for servers, as it nicely minimizes the number of exploits (and the resulting patches) to take care of.
In a traditional (bare metal) world, the whole process is ...
4
votes
2answers
440 views
Experience with other EC2 kernels
I'm curious if any of you have used any of the non-amazon-provided EC2 kernels with success? Canonical seems to provide newer kernels (2.6.28, eg), but there are some mixed reviews about their ...
4
votes
0answers
68 views
Enable SMP on Debian i386?
I've been running a couple old HP machines on Debian for a while, and only recently noticed that they were only 'recognizing' and using one processor. cat /proc/cpuinfo only shows output for processor ...
3
votes
3answers
3k views
3
votes
2answers
278 views
How any routing protocol packet reaches(flows of operations) from NIC card (physical layer) to any Routing (OSPF/RIP/BGP) daemon?
The problem is rearding the routing protocol packet flow in any linux/unix device where multiple routing protocol daemons are running.
How any routing protocol packet reaches(flows of operations) ...
3
votes
6answers
1k views
How do I know what the server is doing when crashing?
I have a server running on Centos 5.2 and is there any a better way to know why the server crashed or what it's doing at that time?
I am sorry I am a newbie and any help is appreciated~ Thanks
3
votes
3answers
601 views
Journaled filesystems and power failure
I heard that even a journaled filesystems such as EXT3/EXT4 might corrupted during power failure, e.g. from wikipedia [1]:
In the event of a system crash or power failure,
such file systems are ...
3
votes
1answer
1k views
Automatic Reboot after Kernel Panic
I am currently running Ubuntu 9.04, Jaunty, and have had some issues that caused a few kernel panics to crop up. These panics cause the system to dump a bunch of information to the terminal and hang.
...
3
votes
2answers
260 views
“Never take kernel updates” — Any truth to this?
So I am having a discussion with a coworker today, and he let something out that I thought was bizarre, as I'm getting ready to apply security updates to one of our production servers.
"You should ...
3
votes
3answers
65 views
How to determine if a Debian upgrade updated the kernel
Let's say I have just done an aptitude safe-upgrade on a Debian system, but I was not paying attention so I did not notice if the kernel was updated or not.
How can I now determine if there was a ...
3
votes
4answers
307 views
Server randomly freezes
Im facing a very strange issue, my debian squeeze freezes up always at night (Berlin, time).
Here is what i get from a time and after doing this a few times, it becomes frozen and must be hard-reset.
...
3
votes
2answers
301 views
Tell the linux kernel to put a file in the disk cache?
Is there any command to for a file to be read in and loaded into the linux disk cache? This is on an up-to-date debian system.
I know in the general case, it's better to let the linux kernel figure ...
3
votes
2answers
4k views
How do you check the version of a *.ko kernel module in Linux?
I know you can do:
sudo modprobe -v some_module
to check the version of /lib/modules/.../some_module.ko, but I'd still like to be able to check the version of any arbitrary kernel module that's not ...
3
votes
2answers
8k views
Debian: logging of SSH failed login attempts?
I just typed a wrong password for login to ssh @ root.
I went to
/var/log/faillog
But the file is empty ( tho its filesize is: 32 Byte )
Ok in auth.log is spammed this:
reverse mapping checking ...
