The Linux kernel is the operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software.

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32
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5answers
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Intentionally cause an I/O error in Linux?

Is there anyway, with Linux, to purposely cause a block device to report an I/O error, or possibly simulate one for testing purposes?
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9answers
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Maximum number of files in one ext3 directory while still getting acceptable performance?

I have an application writing to an ext3 directory which over time has grown to roughly three million files. Needless to say, reading the file listing of this directory is unbearably slow. I don't ...
12
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2answers
473 views

Why does /proc/net/tcp6 represents ::1 as ::100:0

I was writing an utility to check /proc/net/tcp and tcp6 for active connections as its faster than parsing netstat output. As I dont actually have ipv6 enabled I was mainly utilizing localhost as my ...
12
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2answers
6k views

Linux memory fragmentation

Is there a way to detect memory fragmentation on linux ? This is because on some long running servers I have noticed performance degradation and only after I restart process I see better performance. ...
10
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2answers
8k views

Effects of configuring vm.overcommit_memory

My VPS web server running on CentOS 5.4 (Linux kernel 2.6.16.33-xenU) irregularly (like once a month give or take a few weeks) becomes unresponsive due to oom-killer kicking in. Monitoring of the ...
10
votes
2answers
284 views

Linux kernel detecting wrong processor frequency

After a cold boot of a 6.0.8 Debian server (HP ProLiant), ntpd played havoc with system time: offset and jitter with respect to the usual and reliable reference time servers growing without limit. ...
9
votes
3answers
3k views

1000 HZ linux kernel necessary if I have tickless and high resolution timer?

I am trying to improve performance on my server. I have a few processes that need low jitter (less than 10ms variance). I have a load average of 4 maximum on an i7-920 (4 physical cores, 8 with HT). ...
9
votes
4answers
2k views

tc u32 — how to match L2 protocols in recent kernels?

I have a nice shaper, with hashed filtering, built at a linux bridge. In short, br0 connects external and internal physical interfaces, VLAN tagged packets are bridged "transparently" (I mean, no VLAN ...
8
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2answers
6k views

How can I tune the initial TCP retransmit timeout?

The initial TCP RTO value of 3s is too long for most LAN-based applications. How can I tune it lower? Is there a sysctl?
8
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2answers
720 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
5answers
776 views

Convey multicast (to another LAN) through WAN disabling multicast

My Server and Client softwares run both on Linux. The Server broadcasts multicast, the Client listens multicast. My Client has to migrate to another site, and unfortunately multicast is not allowed ...
7
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3answers
6k views

How can I see logs in a server after a kernel panic hang?

I am running a production gentoo Linux machine, and recently there was a situation where the server hung in my co-located premises and when I got there I noticed that the server was hung on what ...
7
votes
1answer
5k views

Flush processes consume too much of CPU

The Server is EC2 Instance, it stands for saving files to NAS (NFS) from HTTPD. The processes like flush-0:32 consume over %90 of CPU and load average: 65.50, 64.02, 66.59. According the graph, it's ...
7
votes
4answers
708 views

MySQL 5.5 degraded performance in linux kernel 3.2 compared to 2.6

Our database servers (mainly based on the Debian stable packages (=currently Wheezy) seem to have about 4 times more load for the same workload in kernel 3.2.0-4-amd64 then in it's previous ...
6
votes
2answers
572 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
7k views

How do I set the default kernel parameters in CentOS for all existing and future kernels?

I'd like to remove the rhgb and quiet kernel parameters which are used by default when the kernel is booted in CentOS 6, but I want this to apply to all currently installed kernels as well as any ...
5
votes
4answers
20k views

In CentOS 6.x, how can I upgrade to Kernel 3.4?

I have a server with CentOS 6.2 with kernel version 2.6.32, but I need to increase my application Performance. The Kernel Version 3.4 has x32abi which can improve the performance so i want to upgrade ...
5
votes
2answers
332 views

Please explain the following o/p of “top” command

Please explain the following line from the "top" command in the bold :- Mem: 1026228k total, 449640k used, 576588k free, 44812k buffers Swap: 1052248k total, 2020k used, 1050228k ...
5
votes
0answers
1k views

Multithreading with multi-queue NIC on SMP system [closed]

How are packets scheduled from network interface queues to CPUs, then onwards to threads for processing? What needs to be considered when it comes to how packets are hashed across queues, hardware ...
4
votes
1answer
104 views

CVE-2014-0196 Vulnerability for CentOS

Trying to patch CVE-2014-0196 Vulnerability but yum can't find packages updates CentOS 6.5 (Final) Panel version: 11.0.9 Update #61 # uname -r 2.6.32-358.11.1.el6.x86_64 # yum update kernel Loaded ...
4
votes
1answer
3k views

how do i set hard and soft file limits for a non-root user at boot?

I have a xen HVM vps and I'm trying to raise the hard and soft file limits for nobody at boot time. I'm using Ubuntu 10.04.3 and inside /etc/security/limits.conf I have: nobody soft nofile ...
4
votes
1answer
7k views

why is kswapd using high CPU on an idle system?

I have an idle Linux centOS system and yet kswapd is using 100% cpu. All I have running is a single bash session with top running.... I have 32G RAM and yet kswapd is constantly using 100% cpu for ...
4
votes
2answers
245 views

Linux: echo 3 > /proc/sys/vm/drop_caches takes hours to complete

I have a Thecus N8900 NAS, which is a Linux based file server, providing files via NFS to six clients. For some reason that Thecus support has yet to explain, it runs a script that checks ...
4
votes
1answer
551 views

Meaning of tcp_delack_min

the current Linux Kernel (e.g. 2.6.36) uses Delayed Acknowledgments (delack). In /include/net/tcp.h it says: define TCP_DELACK_MIN ((unsigned)(HZ/25)) So, for a Kernel using a HZ value of ...
3
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1answer
196 views

How can I tell the kernel to free cached memory during memory allocation request instead of the OOM killer terminating the application

I am running Ubuntu 10.04 with the below kernel version Linux ip-10-0-1-119 2.6.32-343-ec2 #45-Ubuntu SMP Tue Feb 14 18:18:17 UTC 2012 x86_64 GNU/Linux The memory status shows that the cache is ...
3
votes
3answers
2k views

PostgreSQL won't start because it “Cannot allocate memory”

I'm running PostgreSQL 8.4.5 on Ubuntu 10.04. I run an EC2 instance with a few sites running on nginx. Most of these sites run on Django and connect to this Postgres instance. For some reason, at ...
3
votes
1answer
61 views

How to force logging all terminal actions on Ubuntu 12.04 server?

I believe my server has just got compromised interactively. As this server will go to thrash anyway, I wonder if I can get a better insight of what the villain is doing by forcing logging of all ...
3
votes
1answer
419 views

Installed 2TB disk in ubuntu server, dmesg reports it as 9444732965540666 MB

I've have an ageing Linux server running on Dell PowerEdge hardware, with a SAS 5IR RAID controller. It has a pair of SAS 146Gb disks in a RAID 1 configuration that has the OS and other software. I ...
3
votes
2answers
7k views

What is mdev and how to /dev/* nodes get created in Linux?

Our Linux kernel is 2.6.31 running on an embedded MIPS processor with busybox. The initialisation script (rcS) starts mdev with: echo "/sbin/stbhotplug" > /proc/sys/kernel/hotplug mdev -s Can ...
3
votes
1answer
193 views

Linux (non-transparent) per-process hugepage accounting

I've recently converted some java apps to run with linux manually-configured hugepages, as desribed here. I point out "manually-configured" because they are not transparent hugepages, which gave us ...
3
votes
1answer
183 views

What is the interrest of playing with drop_caches?

I've seen sysadmins playing with /proc/sys/vm/drop_caches (echo 3 into this file from a cron) in order to free caches. Is there a real interrest in doing this? Aren't the clean caches reclaimed when ...
3
votes
1answer
3k views

Linux kernel crash - any ideas?

Been getting these runaway conditions on a lightly loaded vps (debian squeeze kernel 2.6.38-bpo.2-amd64, 2GB, SSD) - top load is nothing , then jumps to 30.0 & everything grinds to a halt. I'm ...
3
votes
1answer
3k views

Our embedded linux system won't recognize a USB Device if it is plugged in before powerup. Suggestions?

We are developing on a small embedded device. This device us a gumstix overo board running OpenEmbedded linux. We have our development almost completely done, and have run into the strangest of bugs ...
3
votes
1answer
63 views

Linux kernel thread dependency graph?

I'm trying to benchmark a system with a software RAID-10 volume, backed by Fusion IO cards. Is it possible to display a Linux kernel thread dependency graph? I would like to know how all the ...
3
votes
1answer
401 views

linux initcwnd and initrwnd via /etc/sysctl.conf

Folks, As we know, the 3.x kernels have higher TCP default connection values, such as initcwnd and initrwnd. For 2.x friends, is there a way to set these in /etc/sysctl.conf instead of the ip route ...
3
votes
1answer
1k views

Linux buffer cache effect on IO writes?

I'm copying large files (3 x 30G) between 2 filesystems on a Linux server (kernel 2.6.37, 16 cores, 32G RAM) and I'm getting poor performance. I suspect that the usage of the buffer cache is killing ...
3
votes
3answers
1k views

Munin “Available entropy” when using address space layout randomization

Having just configured Munin for statistics logging on my gentoo server (hardened profile), I am noticing that my "Available entropy" is consitently in the 200-300 range. This seems way to low, so I ...
2
votes
2answers
304 views

Linux process swap usage is greater than the overall system swap usage

I have a strange problem that when I run top command it shows that some processes are using around 1.5GB of swap space but then the overall usage of the system swap is way to less to something around ...
2
votes
4answers
5k views

Debian on Hyper-V

I installed Debian with kernel 2.6.32-5-686 on a Hyper-V virtual machine. I had to add a legacy network card. I follow this tutorial ...
2
votes
1answer
939 views

Cannot find network subsystem in cgroup on Ubuntu 12.04 LTS

I'm trying to use cgroups to limit a process's network bandwidth, as described in this answer. However, I am unable to find the "files" they refer to. I am using Ubuntu 12.04 LTS with cgroup-bin ...
2
votes
1answer
228 views

Do i have to install vmware tools on ubuntu server

its a bit silly Question, I was thinking since i have some spear HW to install ESXi free edition and allow some external users to use prebuild ubuntu 10.04 servers. since with kernel updates etc etc ...
2
votes
1answer
1k views

Limit the number of max threads used by a process in linux kernel

I think I have found something that I need from the Linux kernel that is not currently implemented. I need a way to set a max thread limit per process. Is this possible?
2
votes
2answers
536 views

Time drift in Cloud Server - need to mainpulate GRUB config

We are hosting a VPS on a popular host and are experiencing a regular time drift of several minutes a day forward (approx 7). Linux Kernel: 2.6.18-164.11.1.el5 GNU/Linux Distro: CentOS release 5.4 ...
2
votes
1answer
94 views

How can I make my own linux distro? [closed]

My question is bit off-topic or may be impractical. The thing is, on the web too many material available to download customized linux distro. But what if I want to make my own linux distro ? ...
2
votes
1answer
55 views

Linux Kernel setup: is it good idea to enable everything in Cryptographic API?

There are several implementations for some algorithms, which use CPU instructions which may or may not be available on current system. Is it good idea to just enable (in kernel, not as modules) all of ...
2
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1answer
1k views

Where are the acpiphp and pci_hotplug kernel modules for KVM hotplug in CentOS/RHEL?

On the this how-to I read the following: I loaded the following modules to get pci hotplug working: acpiphp pci_hotplug You can either add these to your distro's module list to ...
2
votes
0answers
34 views

how to determine who is using the slabs?

Is there any way to figure out who or what is allocating size-256 slabs, like in the slabtop output below? I had to reboot a server yesterday that had 5G out of 8G RAM in size-256 slabs and was ...
2
votes
0answers
212 views

Should I set rto_min for a route inside data center?

We have a few dedicated server rented in a data center with debian 7, kernel 3.2. We use one of those servers as a database server. The network between our application server and database server is ...
2
votes
0answers
49 views

Sun Fire V40z, big gap between memory reported by dmidecode and what the Linux kernel sees

I'm looking after a V40z (a loaner), running RHEL 4.8 (no, I can't update it, it's a loaner) that according to dmidecode has 8 DIMMs of 2048M each, which makes for 16GB RAM as far as I'm concerned. ...
2
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0answers
403 views

netmap issue with wheezy linux kernel 3.2.0.4 and Intel Corporation 82599EB 10-Gigabit card

I have compiled the netmap drivers on debian wheezy with kernel 3.2.0.4 and ixgbe patched module from netmap drivers code. When I insert the modules after removing default ixgbe module I get the ...