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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TCP buffer sizes and ethernet bonding

(This question was originally posted on stack overflow; Andy told me that I could get faster help here, so it is re-posted here now.) I am experimenting with TCP buffer size tuning on Linux, but ...
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'BUG: unable to handle kernel NULL pointer dereference at' on Google Compute Engine

On a semi-regular basis, I've seen GCE instances freezing with the following error message (from the serial console): g[1375589.784755] BUG: unable to handle kernel NULL pointer dereference at ...
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55 views

mdadm - stuck reshape operation

I have a 3 disk RAID 5 array that I tried to add a 4th disk to. mdadm --add /dev/md6 /dev/sdb1 mdadm --grow --raid-devices=4 /dev/md6 This operation started successfully and proceeded until it hit ...
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Kernel Crash - kernel: BUG: unable to handle kernel paging request at 00000000ff8179b9

One of my Oracle Linux 6.5 Server running Oracle ASM/GRID experienced a kernel crash, it didn't respond i have performed a hard reboot. Server is Oracle Linux 6.5, kernel 2.6.39-400.214.3.el6uek....
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How to reliably capture Linux kernel log messages in case of a system debilitating crash (BUG, panic)?

I'd like to have access to the lines/tracebacks/whatever whispered by the kernel right before dying. This has proven problematic, because all interfaces I have access to become disabled. Post-reboot, ...
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446 views

strace not showing anything for thread at 100% 'system' CPU

I'm having difficulty with my Python app going to 100% 'system' CPU time across multiple threads for up to 10+ seconds. My (limited) understanding is that 'system' CPU time is time spent in the kernel....
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161 views

What are the advantages NAPI before the IRQ Coalesce?

As known there are two approach to avoid some overheads of hardware interrupts in highload networks, when there are too many hardware interrupts, that switching to them takes too much time. It is very ...
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118 views

“Nosy Neighbor” and the CFQ scheduler

I'm trying to understand how does using CFQ affects the "Nosy Neighbor" problem. I'll ask it a bit naively, can a "Nosy Neighbor" even exist when using CFQ? Isn't that CFQ should make sure all ...
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__ticket_spinlock high cpu

We are having a strange problem on our Ubuntu 10.04 KVM infrastructure, where periodically, one of two vm webservers freaks out, with persistently high load, even if we restart the applications. (the ...
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1k 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 ...
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64 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. ...
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576 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 ...
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435 views

KVM host kernel configuration for best performance

I'm currently building a kernel for my server, which should serve for hosting virtual machines using KVM. There are a few kernel configuration options that are already described in the KVM-Wiki. The ...
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113 views

Segfault in libc-2.19.so with Webmin

I recently upgraded the kernel one of my Debian 8 servers which has Webmin+Virtualmin installed on it. The server had usual Virtualmin backups setup which used to work fine before the upgrade, but ...
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46 views

memory usage reporting by kernel in log when task is killed due to OOM

My task inside docker container are getting killed due to OOM. Here is a log from /var/log/messsages. Feb 17 19:01:24 ip-10-0-1-85 kernel: [16211.346602] uwsgi invoked oom-killer: gfp_mask=0xd0, ...
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37 views

Strange messages in my syslog on Debian

I am getting strange messages on my /var/log/syslog that aren't usual. I am running a Debian Jessie LXC Container inside of a Debian Wheezy machine. But I believe this is not the problem. An example ...
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70 views

How to increase the amount of memory used for caching on 32 bit Linux?

I have a server with 64 GiB RAM running 32 bit Debian GNU/Linux v7.9: # uname -a Linux srv1 3.2.0-4-686-pae #1 SMP Debian 3.2.68-1+deb7u5 i686 GNU/Linux # free -m total used ...
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118 views

Auto-Reboot on Kernel BUG (not tainted, “fixing recursive fault but reboot is needed”)

I'm running a sometimes highly loaded Debian 7 VM with the latest 3.2.x kernel on a XenServer 6.2 host. Sometimes this VM runs into the following state: Ping is okay, All Services unreachable (...
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2k views

sysctl: cannot stat /proc/sys/kernel/exec-shield: No such file or directory

Enable ExecShield protection - ExecShield is security Linux kernel patch to avoid worms and other problems. After Adding to /etc/sysctl kernel.exec-shield = 1 Getting this error sysctl: cannot ...
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83 views

Server crashes because of SMP

My web server is crashing every few days unless I disable SMP with "nosmp" parameter in Grub config. It is not an hardware failure because the problem persists after moving everything to a new machine....
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529 views

“error: ‘PATH_MAX’ undeclared” when trying to make menuconfig

I have an OVH cloud VPS with Ubuntu 14.04 64 bit server. I needed linux headers which OVH does not provide by default, so I found some tutorials on how to compile the linux kernel from source using ...
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280 views

PCIe card memory regions ignored on linux kernel 3.13

On my system, with kernel 3.13.0-32-generic (Ubuntu Server 14.04.1 LTS) installed, one of the PCIe boards in the system (06:00.0) is having it's memory regions ignored: Interrupt: pin A routed to IRQ ...
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148 views

The default value for vm.dirty_background_ratio

Wondering why the default value for "vm.dirty_background_ratio" from Linux Server (CentOS and Ubuntu) is set to 40. Is this just a recommendation for safety? Or is there any particular reason why? ...
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192 views

linux not replying to an arp request

I am running linux 3.14 on a system with 2 interfaces. on the first interface, i can access our local network. on the second interface, arp packets come in but linux doesn't send out reply. is it ...
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191 views

task fstrim blocked for more than 120 seconds

I'm experiencing random crashes on my system. I've narrowed the problem to the fstrim program that's launched weekly by cron. In the console, I've got a set of blocked tasks among whigetch I find ...
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320 views

shorewall can'T start: UNTRACKED state requires Raw Table in your kernel and iptables

I'm trying setting up my firewall and installed and configured shorewall. Unfortunately I tried to directly configure iptables first, but this didn't work. When I start shorewall, I get this messages ...
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246 views

ext3 option on error doesn't work

I have a redhat server 5.8 with ext3 on top of lvm, i noticed ext3 has setting "Errors behavior: Continue" in the fs super block, from the man page of mount command i readed this errors=...
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257 views

Capturing on loopback device on Ubuntu LTS: 15 Mbit of traffic and “x dropped packets”

I am trying to capture about 15 Mbit of traffic on the loopback device on Ubuntu LTS using tcpdump, and I am seeing dropped packets. The CPU is a freaking i7, and i have yet to see CPU usage go above ...
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243 views

linux kernel configuration to filter multicast traffic based on interface

I have two virtual interfaces (eth0.2, eth0.3) in my PC. I am sending multicast data from eth0.2 to eth0.2. Multicast data is received in eth0.2 but also received in eth0.3, the other virtual ...
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211 views

Tracking huge buffer usage under Linux

I'v a Linux server running under Debian Lenny with 4Go of RAM. It doesn't run a large number of stuffs: Postfix/spamassassin (daemon mode) Bind9 KVM (one guest - 1Go of RAM for it) Every day at ...
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615 views

How to modify Ubuntu 10.04.1 Grub entry for supporting KGDB kernel image

I am trying to update target m/c grub.cfg file for KGDB setup but while booting the m/c it got hung completely and not asking/waiting for remote gdb connection. Following is the entry which I added:- ...
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Change kernel of Centos OVH

I'm using a server of OVH with OS centos7. OVH has its own linux kernel: 3.14.32-xxxx-grs-ipv6-64 Now I try to configure another Centos7 kernel. I installed the other kernel(s). yum install kernel ...
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44 views

How to I reconfigure grsecurity patch on Debian kernel

I installed the linux-image-4.4.0-1-grsec-amd64 on Jessie from the Debian package repo. Having issues with LXD and grsec Chroot restrictions, I went to make adjustments to /etc/sysctl.d/grsec.conf ...
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cgroup same process with different resources

I have a Jboss application server installed through source and running multiple instances(say 3) of JBoss as a same user in a single machine on different ports. Using cgroups, I'm trying to do ...
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48 views

Kernel headers not found in Cent OS 7

I was trying to install ixgbevf drivers. # dkms build -m ixgbevf -v 2.14.2 Error! echo Your kernel headers for kernel 3.13.0-74-generic cannot be found at /lib/modules/3.13.0-74-generic/build or /lib/...
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Building CentOS kernel from RPM with patches (but missing files that are in the SRPMs)

I have a hardware system that I am running CentOS 7 on. I would like to add some patches to the default CentOS kernel, since I have some custom hardware to support, but I also want to track the ...
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Configuring vxlan unicast in linux

I want to try vxlan unicast and configured following configurations in Fedora 23 VM1(enp0s8) ========= (enp0s8)VM2 ip address add 100.1.1.1/24 dev enp0s8 ifconfig enp0s8 up ip link add name vxlan42 ...
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kernel: OUT setsockopt exception observed in syslogs

We are facing the issue of sudden reboot of the machine. There are no errors in the iLO logs. We are observing below exception repeatedly in the syslog, which I am unable understand. kernel: ###OUT ...
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24 views

Why is my scaling_max_freq stuck at 1GHz (on a Core Duo processor)

I recently setup an old Thinkpad T60 as a secondary desktop (via a docking station), but when I tried it, it was feeling sluggish and I soon figured that it was somehow stuck at 1GHz, even tho its ...
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Install kernel modules during an ParaVirtual to HVM AWS instance upgrade

I am trying to create a clone of a PV AMI to an HVM one. The PV AMI is an Ubuntu 12.04 and I cannot upgrade that version. I do have a base Ubuntu 12.04 that is HVM enabled with Enhanced Networking. ...
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19 views

How to handle this warning: The Linux source in /lib/modules/3.19.0-25-generic/build has not been configured

I am trying to install a Sangoma PRI card on a Ubuntu 14.04 LTS. During installation of the drivers, it gives me this warning, followed by other errors which are a consequence of this issue (or so I ...
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71 views

Linux vm.vfs_cache_pressure affect page cache or not?

I want to limit page cache in linux. Some documents say increase vm.vfs_cache_pressure to control the kernel reclaim memory. I try, but not work. Linux/Documentation/sysctl/vm.txt say "Decreasing ...
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How to build configfs kernel module externally

I've used the standard make -C /usr/src/$(uname -r) M=$(pwd) modules invocation to build many out of tree modules before (ath, e1000e, etc). Despite being defined as a tristate (tristate "Userspace-...
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How to troubleshoot strongswan error: “unable to allocate SPIs from kernel”?

I am trying to setup an IPsec tunnel to a Juniper security gateway using a strongswan client on a Linux machine and preshared keys. This is what I get when trying to bring the connection up: root@...
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53 views

TCP sockets dying on LTE

I have about 25 audio streaming clients built on an i.mx6 arm platform, running linux version 4.3.0-rc2-00019-gbcee19f-dirty #36 SMP Tue Feb 9 15:27:51 EST 2016 armv7l I find on two specific units ...
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tcp receive buffer size min value seems not work

I tried to increase tcp min receive buffer size to 87380, so in my test it would OOM quickly with a little connections. net.ipv4.tcp_rmem = 87380 87380 6291456 net.ipv4.tcp_wmem = 87380 87380 ...
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78 views

Xen VGA passthrough w/ XEN_PCIDEV_BACKEND kernel option

Xen's webpage ( http://wiki.xenproject.org/wiki/Xen_VGA_Passthrough ) says this is a requirement for VGA passtrough: "dom0 Linux kernel needs "XEN_PCIDEV_BACKEND" option enabled." I'm running ...
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Easy way to send local configuration to server

Pretend I have setup a server hosting for a website locally (on my Linux laptop), it all works perfectly. It has all of the files for the website, firewall has been setup, apache install etc... For ...
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136 views

Debian Preseed: Installation process stuck at 18 % at finishing-installation

My Preseed installation of Debian is stuck at 18 % and i don't know what's wrong. Can you help me please? Here is syslog screen: Syslog Here is my preseed file: #C ontents of the preconfiguration ...
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72 views

Troubleshooting with kernel call trace and underlying root cause with XFS

How to determine the root underlying cause of an error when looking through a Linux kernel call trace, and in which order should I read the call trace? From my understanding, the call trace should ...