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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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Is there a command or script which can pull out list of binaries and lib's installed using make and rpm separately [on hold]

Is there a command or script which can pull out list of binaries and lib's installed using make and rpm separately For example let us consider I have 5 packages installed using rpm and 5 packages ...
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High system CPU utilization

I have a server hosting an Oracle database. It's a 12x2 core CPU with 64GB of RAM running on RHEL5. Lately I've been noticing some sluggishness on the server, upon checking through TOP I found that ...
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Are these errors in dmesg (related to PCI/NVME drive) anything to be concerned about?

Anyone know what this error below (dmesg output) indicates? I'm getting it when periodically writing to an Intel NVME drive (attached to a PCI card) under Linux. Not sure if "no further action" means ...
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How to enable IBRS when it is disabled?

I have been updating some servers to the latest patchlevels and wanted to check the security state regarding Meltdown, Spectre and Spectre-NG. Using the current V 0.39+ of the spectre-meltdown-...
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iptables: Rate too fast Error

I want to set hard limit for incoming UDP packets on my Linux machine which is inside 10 Gigabit LAN. Following command works fine /sbin/iptables -A UDP-LIMIT -m limit --limit 10000/s --limit-burst ...
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amd_iommu=force_isolation.what does it mean?

When I use iommu to passthrough sriov device,I find all VFs and PF are in a same iommu group. Can I use “amd_iommu=force_isolation”? Does it mean every device will have a single IOMMU Group? Does it ...
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cannot boot to the newly compiled kernel version

I have a server with RHEL 7.5 OS. The inbox kernel version on the system is 4.14.0-49. I have a requirement to use the latest available kernel, so I downloaded the Kernel 4.17.18 source package and ...
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60 views

IPv4 identification field manipulation in linux

When Don't Fragment flag is set, IPv4 RFC allows set Identification filed to 0x0000. I got a peer which is behind firewall that brakes RFC and block any IPv4 packets with such 0x0000 ID field. My "...
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How can iperf reporting packet loss in udp

Iperf is the well known tool to calculate throughput. When i tried udp throughput using iperf on my linuxpc, It reported that 10% of packet loss. In UDP protocol, data gram did not receice any ...
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Centos 6.8 kernel 2.6.32-642.el6.x86_64 crash at linux-2.6.32-642.el6.x86_64/mm/vmalloc.c: 630

I have intel servers running CentOS 6.8 as KVM host,and there was an OOPS or BUG occurs. kernel crash at kernel-2.6.32-642.el6/linux-2.6.32-642.el6.x86_64/mm/vmalloc.c: 630 Did anyone else have this ...
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Linux - memory size

How to check exact amount of memory installed in server? MemTotal from /proc/meminfo show something a bit less. I.e. I have 2097152K and meminfo says 2054348K. I can sum all banks reported by ...
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CPU utilization impact due to granularity kernel parameter RHEL6 vs RHEL7

Following kernel parameters are showing very different behaviour from R6 to R7 and we are not able to figure out why. Any help appreciated. kernel.sched_min_granularity_ns kernel....
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Why in CoreOS Kernel parameter sotflockup_panic is activated?

I looked through different Linux distros such as Ubuntu, CentOS, openSUSE, RHEL, PhotonOS, and Alpine for kernel parameter softlockup_panic. In all of them this kernel parameter is deactivated. # ...
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When someone gains remote access to a server are there other ways to execute system commands other than the bash shell?

I am hardening a server and attempting to build a restrictive layer to a potential hacker even with root access to the server to do harm. If a user gains root or user access to the shell via say ...
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How to tune the performance of a Nginx webserver in ubuntu16.04 [duplicate]

My server is ubuntu 16.04 and 8 core machine with 16gb RAM. I need to get the best performance with this configuration. How can I tune the server with Nginx level and system level? Running a PHP LMS ...
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Can /boot/efi partition causes issues for kernel boot?

I have a fresh installation of CentOS 7 on a server. I have manually partitioned system and, per installer suggestion, I have created /boot/efi (never asked for that before). After the installation ...
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localhost kernel: possible SYN flooding on port 8222. Sending cookies

I get this error message(centos 6): Jun 12 07:42:40 localhost kernel: possible SYN flooding on port 8222. Sending cookies. Jun 12 08:07:05 localhost kernel: possible SYN flooding on port 8222. ...
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145 views

Are Kerberos service tickets cached by mount.cifs or kernel?

When mounting a CIFS share using krbr5i and destroying my Kerberos tickets with kdestroy afterwards its still possible to mount other shares on the same server. How is this possible? Doesn't mount....
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406 views

ZFS datasets no longer automatically mount on reboot after system upgrade

I have an Arch linux ZFS backup system which wasn't updated for a long time because it was working perfectly and there was no reason to bother. After a recent upgrade, though, my ZFS datasets are no ...
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93 views

What are the parameters in iostat

I used iostat and trying to understand the iostat output using this link : https://linoxide.com/linux-command/linux-iostat-command/ but It is not clearly explained. PF the output at different times ...
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linux (ubuntu 17.10) fan stopped working

At some point recently, my fan stopped working. I've confirmed it's not the hardware, because in the bios I can start and stop the fan. This is an ubuntu 17.10 desktop host. I noticed that lm-...
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How to setup nvmetcli for FC loopback mode?

I have a NVMe SSD, KC1000, from Kingston and a HBA, QLE2672 2-port 16Gb Fibre Channel Adapter, from QLogic and are installed on Linux kernel 4.16.6. Then I would like to set up a scenario which has a ...
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How to count the packets inside Linux network namespace using NETFILTER framework?

I am newbie to Netfilter. Trying to implement netfilter framework (INPUT-HOOK, OUTPUT-HOOK, FORWARD-HOOK) in Linux to count the number of packets went inside the network namespace. But not able to ...
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123 views

Improve single HTTP transfer bandwith over high latency connection (Ubuntu Linux)

I'm trying to improve the file transfer speed for my web server in Roubaix, France (hosted by OVH) over high distance/latency connections. I know that TCP connections are affected by higher latency, ...
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Redhat vs Oracle Linux benchmarks

I have two servers, both have Intel 8160 processor, 768 GB memory, same hardware specs, same software/package versions. The only difference being that one is running RedHat Enterprise Linux 7 and the ...
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iptables rejected message log references another message in '[…]' - is that other one real?

I've got a set of rules in my iptables to detect, log, and drop "conntrack-invalid" packets: -A local-before-input -m conntrack --ctstate INVALID -j local-conntrack-invalid -A local-conntrack-invalid ...
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1answer
166 views

I can't connect to my AWS server after yum update on centOS 7

I created a new server (EC2) with centOS 7, and after the first "yum update" and a reboot I can't connect anymore. =====================================================================================...
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334 views

Kernel Panic on Guest-VM (Debian 9)

I have two servers running with Debian Jessie Kernel 3.16.0-5-amd64. Both servers have the exact same configuration, only hardware differs. I use KVM as hypervisor together with QEMU on both servers. ...
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Nice not working though disabled kernel autogrouping via sys.kernel.sched_autogroup_enabled

Context I have a Ubuntu 16.04 Kernel 4.4 desktop installation and two randomly CPU-intensive tasks (docker, numbercruncher). I want to prioritize the docker process over the numberbruncher task, ...
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1answer
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Diagnose Sudden Slowness on Linux

I have two identical Linux laptops (Core™ i7-4810MQ with 32GB RAM) both running Ubuntu 16.04. Running seemingly any command on machine 2 takes about 4-12 times as long as on machine 1, depending on ...
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Where to get newer RHEL 7 kernel mentioned on bugzilla.redhat.com (for CentOS)

I am using Centos 7.4 and have encountered a bug, which I found a solution for: https://bugzilla.redhat.com/show_bug.cgi?id=1502601 The problem is, solution mentions that bug is fixed in kernel-3.10....
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Ubuntu kernel source code for AWS instances

I'm trying to find the source code for a specific AWS kernel - ubuntu instance (e.g. linux-image-4.4.0-1022-aws). The ubuntu kernel git repository doesn't have tags for these AWS instances. Please don'...
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72 views

zram filesystem reports different usage at device level to that reported by the filesystem

We have an 80GB zram device defined on our host, and within this a 170GB ext4 filesystem: echo 170G > /sys/block/zram0/disksize echo 80G > /sys/block/zram0/mem_limit /usr/sbin/mkfs.ext4 -...
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1answer
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VGA monitor blinks with KVM

Tried using several computers with a KVM switch that uses the 25th port on the VGA connection for USB (for the keyboard and mouse - StarTech.com SV1631DUSBUK). Manufacture says the cable they use to ...
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dmesg - suspend of devices in a vm

On my virtual machine (xen platform) I can see a periodic: [13178922.944967] PM: suspend of devices complete after 0.091 msecs [13178922.945059] PM: late suspend of devices complete after 0.074 msecs ...
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1answer
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Cannot explain memory occupancy in linux

I'm working on a debian 9.3, the free command return total used free shared buff/cache available Mem: 131940516 100433176 29189576 33940 ...
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1answer
56 views

Misunderstanding about Page Cache and dirty_background_bytes

I've been looking at this for a while now and things aren't lining up with my expectations, but I don't know if it's because something is off, or if my expectations are wrong. So, I've got a system ...
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How to enable/install kernel-debuginfo linux-4.14.14 on amzn-linux? [duplicate]

I'm on an amzn-linux instance which by default runs linux-4.9. I've compiled and booted linux-4.14.14 from source and I've compiled systemtap from source. Now I'd like to get them both working nicely ...
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1answer
839 views

Resetting / Modifying network configuration in Centos 7 Rescue mode

I've a dedicated server CentOS 7 and i made a wrong configuration for it /etc/sysconfig/network-scripts/ifcfg-enp2s0 So after restarting the network drive, the server went down .. So i've a copy ...
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BUG: soft lockup - CPU#0 stuck for 22s

I am running some SD-WAN applications like SDN switching, routing etc.., in a GUEST node (Ubuntu Linux) which is Hosted in an Compute node of Openstack environment. Host Node details: admin@:~$ ...
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1answer
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How to prevent useless kernel-modules from loading?

Our Ubuntu-servers all seem to have various unused kernel-modules loaded wasting RAM and, in the case of jfs for example, running a bunch of useless processes (jfsCommit). I can use rmmod to get rid ...
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1answer
383 views

How should we understand this 'locked for more than 120 seconds' call trace?

Yesterday a Java service in our Docker Swarm cluster suddenly stopped responding. The task (container) for this service just hung, did not answer any requests, and could not be killed. Looking at /...
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577 views

Network interface periodically going down with speed changed to 0 kernel errors

Over the last couple of days, the bonded network interface on one of our servers has stopped responding. Looking through the kernel logs, I notice when the interface goes down, we are getting lots of ...
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1answer
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How to restrict root to access a directory used by other user with selinux

I want to restrict the root to access a folder/directory which is created by another user.So that only that user can access that folder not even root. Is there any selinux configuration to do so this ...
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Fibre Optic port moving to 1000Mb/s eventhough it is not in the supported link mode

In my Fibre Optic device (Linux 2.6.27, LXT971A PHY Transceiver), connection to the port is lost intermittently. While debugging with ETHtool, the following observation was observed: Settings for ...
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1answer
1k views

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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1answer
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Oracle-asm RHEL 5 Kernel Upgrade Instructions? [closed]

What are the official instructions for upgrading the oracle-asm kernel drivers when performing a kernel update on RHEL 5? I can only find documentation on a clean install of oracle-asm which includes ...
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2answers
767 views

Opening a linux-crashdump dump with crash?

So I've been trying to debug a weird intermittent kernel crash for a server running Ubuntu-Server 16.04, which has had me stumped for ages, and so I installed and setup linux-crashdump following the ...
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1answer
164 views

GRUB_DEFAULT seems to be ineffectual when trying to boot a custom kernel by ID on Debian 8

I've built a custom kernel on a Debian 8 machine, and I want to set it as the default. A seemingly simple task, but I can't get it to work for the life of me. I built my kernel using the official ...
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Kernel panic - not syncing Attempted to kill init after mount

I have a VPS running Debian 8 at OVH. Recently I couldn't connect to the SSH because I received the message: "access denied". So I decided to reset the root password. I followed OVH indications in ...