Questions tagged [linux-kernel]
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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How do I make Linux recognize a new SATA /dev/sda drive I hot swapped in without rebooting?
Hot swapping out a failed SATA /dev/sda drive worked fine, but when I went to swap in a new drive, it wasn't recognized:
[root@fs-2 ~]# tail -18 /var/log/messages
May 5 16:54:35 fs-2 kernel: ata1: ...
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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 ...
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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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What are the performance implications for millions of files in a modern file system?
Let's say we're using ext4 (with dir_index enabled) to host around 3M files (with an average of 750KB size) and we need to decide what folder scheme we're going to use.
In the first solution, we ...
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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 ...
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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. I ...
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Why CPU spent time on IO(wa)?
I know wa (in top) measures the CPU time on waiting for I/O. Many articles say that.
But I am confused that, based on 2 knowledge points:
if a process uses a system call to read disk, the process is ...
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kswapd often uses 100% CPU when swap is in use
Most of the time when my computer starts to need swap, I see a massive spike in CPU usage (kswapd0 is consistently using 99%-100% CPU). According to top, the time is spent in sy (system/kernel) not wa ...
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Difference between net.core.rmem_max and net.ipv4.tcp_rmem
What's the difference between net.core.rmem_max and the third value of net.ipv4.tcp_rmem? Which has the higher priority for tcp connections?
For below two examples, what's the max buffer for tcp ...
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Cause of page fragmentation on "large" server with xfs, 20 disks and Ceph
Any insight from someone with a bit of experience in the linux IO system would be helpful. Here is my story:
Recently brought up a cluster of six Dell PowerEdge rx720xds to serve files via Ceph. ...
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In CentOS 6.x, how can I upgrade to Kernel 3.4?
I have a server running 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 ...
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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?
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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. (...
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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 ...
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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). ...
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CoreOS: tcpdump mysteriously solves network issue (excessive number of sockets used)
I've got a mystery for you today. We run a small, three node Elasticsearch cluster based on CoreOS (2023.5.0 / Linux 4.19.25-coreos) on Azure. Elasticsearch is run inside a docker container in host ...
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How to avoid downtime with linux?
Frequently software updates to Ubuntu require reboots (which can have side effects such as downtime).
I see Ubuntu has https://www.ubuntu.com/livepatch which allows for kernel updates without reboots,...
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How dangerous might it be - and what performance gains may be had - by turning vulnerability mitigations off on non-Internet facing servers?
When a virtual machine Linux host server is non-Internet facing and is used exclusively on a LAN and is using a relatively well tested distribution like Proxmox, how dangerous would it be to turn off ...
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is /dev/dm-1 a partition or a whole block device?
Is there a way to figure out if /dev/dm-1 is a block device partition or a whole block device? If /dev/dm-1 is a partition, is there a way to find out the path to the corresponding whole block device?
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Can't update linux kernel on VPS
I recently started using VPS from OVH: http://www.ovh.co.uk/vps/vps-classic.xml This is likely problem very specific to this one provider.
My goal is to install and run Docker on it, for this I need ...
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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 ...
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How to achieve per-packet multipath routing on Linux?
Linux Kernel before 3.6 used route caching to do IPv4 multipath routing, which meant routing between two separate lines/ISPs was quite easy. From 3.6 the algorithm changed to being per-packet, meaning ...
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How to properly permanent enable ip forwarding in Linux with systemd?
I try to enable ip forwarding (between enp0s3 and tun0 interfaces) and write net.ipv4.ip_forward = 1 in /etc/sysctl.conf. After restart I have
$ cat /proc/sys/net/ipv4/ip_forward
1
But forwarding ...
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Do Containers Have An OS?
I know that containers use the host's kernel and from what I understand , that's the reason we do not need an OS.
My questions are (and I couldn't find any good explanation online) :
1) If that's ...
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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 ...
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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 ...
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Default value of /proc/sys/fs/file-max
I am aware that /proc/sys/fs/file-max defines the maximum number of open file descriptors and can be set on runtime or during boot.
However: what is its default value? Checking 10 servers in my ...
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Why does Linux answer to ARP on incorrect interfaces?
I have the following Linux networking setup: there is an eth10 network interface with the assigned address 10.11.0.1/24. Then there is a tap0 network interface with assigned dummy address 0.0.0.1/32 (...
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Linux: Why does the CPU frequency fluctuate when using the performance governor?
I'm using a Debian 8 amd64 machine for benchmarking. During experimentation, I would like the CPU to operate at a fixed frequency (preferably the maximum possible). This will rule out the CPU clock ...
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View full program command line arguments in OOM killer logs
Is it possible to view full program command line arguments in OOM killler logs ?
What I see now in /var/log/syslog is
Memory cgroup out of memory: Kill process 29187 (beam.smp) score 998 or sacrifice ...
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Why can't QEMU allocate the memory if the Linux caches are too big?
If I use my machine [Ubuntu 16.04 64 bit, kernel 4.4] for a while, QEMU needs the kernel caches to be dropped, otherwise, it won't manage to allocate the RAM.
Why does it happen?
This is a sample ...
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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 ...
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nic: Something Wicked happened! ffff
I'm configuring a GNU/Linux Router with Debian Stretch (9.7) and before rebooting the server, all traffic from one interface to another was going ok, but after that, I received a message like this (...
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How does one diagnose Linux LACP issues at the kernel level?
Is there an underlying administrative or diagnostic interface to the Linux bonding driver to determine what is going on internally?
I've used link aggregation between Linux boxes and Cisco switches ...
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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 dist-...
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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 ...
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Why 224.0.0.1 traffic is filtered by Linux hosts?
When sending an ICMPv4 echo request to a destination address like 224.0.0.1, it is ignored by Linux hosts receiving the request. The destination MAC address used is 01:00:5e:00:00:01.
The only way to ...
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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 ...
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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 ...
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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 ...
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How to compile the kernel with debug symbols? [closed]
I've already finishing compiling the kernel from source,
but how to compile it with debug symbols,what additional steps to I need to take?
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How to disable ipv6 support in Linux entirely?
We are currently setting up a some local network servers to run in a full ipv4 network. I can be sure, that this network don't have ipv6 support, and never will.
Next to that,
partially because of a ...
user266008
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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 /proc/...
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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 2.6.32-5-...
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How to view linux kernel logs live?
I have a kernel module logging input of some sensor while I work with it. I want to see if there is a command that outputs /var/log/messages (for example) but waits for more logs to come. That is, ...
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Linux (non-transparent) per-process hugepage accounting
I've recently converted some java apps to run with linux manually-configured hugepages, as described here. I point out "manually-configured" because they are not transparent hugepages, which gave us ...
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Kernel updates without rebooting
Similar to some of the topics touched on in this question, Is it important to reboot Linux after a kernel update?, I was curious if there was a way in which one could apply kernel updates to the ...
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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 ...
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Debugging kmalloc-64 slab allocations / memory leak
I have two virtual servers that are configured very similarly: Debian bullseye (testing), 5.6.0 kernel, 512 MB RAM. They're both running a similar workload: MySQL, PowerDNS, WireGuard, dnstools.ws ...
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Why can't my Linux kernel reclaim its slab memory?
I have a system that suffered from ever-increasing memory usage until it hit the point where it was hitting swap even for mundane things and consequently becoming pretty unresponsive. The culprit ...
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