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 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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0answers
19 views

How do I force specific interface to use different driver in RHEL?

We have Dell Poweredge 630 server which has 2 NIC Interface. We bought Intel's FTLX85.. module for those 10Gbit ethernets. 2 interfaces were using bnx2x driver of Broadcom. I installed Intel's ixgbe ...
0
votes
1answer
20 views

Recovery action for reserved kernel page: Failed

In a fresh install of 15.10 server, kernel 4.2.0-16-generic, I'm seeing the following entries in my kern.log file: Feb 1 11:49:30 Client-5 kernel: [ 117.847487] MCE 0x1182: reserved kernel page ...
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0answers
17 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 ...
0
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0answers
15 views

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 ...
2
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0answers
24 views

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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0answers
20 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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0answers
28 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 ...
1
vote
1answer
52 views

Linux route unexpected mtu

i'm observing rather strange (at least for me) behaviour for few routes in my network. i use gre interfaces on top of ipsec tunnels. these gre interfaces have mtu 1400 on my entire network. normally i ...
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1answer
32 views

Memory Hotplug in Linux is supported?

Does someone know, if the underlying hardware supports memory hotplug, in Linux is supported without reboot? Especially in Centos 6.x(x86_64). Thanks
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0answers
30 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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31 views

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 ...
0
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1answer
19 views

Clearing cached memory of uploaded file

On my system, I have a log file that is being rotated and uploaded every hour. This file is heavy on writes and only needs to be read when rotated and uploaded. The cached memory on my system is ...
4
votes
1answer
91 views

kswap using 100% of CPU even with 100GB+ of RAM available

I'm running a Centos 7 ESXi VM with almost 300GB of RAM and 24 vCPUs. The average load is 3 and apps almost never use more than 150GB of RAM. The rest of the available memory is used by Linux for ...
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2answers
22 views

patch lists for Redhat linux 5.9 -64 bit

Can any one update the lists of kernel patches released for Linux 5.9 Redhat and what is the current patch level. Thanks Mohan
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2answers
22 views

Using the output of a program as the contents of a file, dynamically

In Linux, I would like to create a file where the contents of the file are dynamically generated by the output of a program. The examples which already exist are /dev/random /dev/urandom, /dev/zero, ...
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0answers
45 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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0answers
56 views

Unusually high dentry cache usage leads to PHP performance degradation

We have lots of servers serving lots of requests with apache and php accessing remote memcacheds. But we are experiencing degradation from php side accessing memcached and obtaining lots of memcached ...
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2answers
56 views

For php webserver, what is faster, 1x 24-core server or 3x 8-core servers? [closed]

Pricing at Dell, it seems I can either get a single R430 or 3x R220's. The R220's would have 4C/8T processors, giving 24 threads. The R430 would have 2x 6C/12T processors giving again 24 threads. For ...
6
votes
1answer
104 views

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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0answers
53 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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votes
1answer
92 views

Centos iptables: No chain/target/match by that name [duplicate]

I had a CentOS6.7 with OpenVZ. Now, I just uninstalled OpenVZ and start using Plain CentOS6.7. Due to some difficulties for using cPanel in OpenVZ. I noticed one problem when install csf in my plain ...
1
vote
1answer
40 views

Linux OOM-killer disabling woes

I have a Linux machine with no swap, which has vm.overcommit_memory=2 and vm.overcommit_ratio=100 set. However these settings seem to have no effect. Some newly-started processes which attempt to ...
1
vote
1answer
83 views

Ubuntu 14.04 TCP established hash table entries

A bit of background I am running two servers under high traffic one with ubuntu 12.04 (linux 3.2.0-69-generic) and one with ubuntu 14.04 (linux 3.13.0-52-generic). I am now trying to secure both. ...
1
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1answer
30 views

Empty fstab on Debian 7 and up. Possible side effects?

When I was checking a machine set up by our sysadmin team, I encountered an completely empty fstab. In fact it was the default fstab installed by a debootstrap. # UNCONFIGURED FSTAB FOR BASE SYSTEM ...
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2answers
69 views

Hide kernel messages in plymouth

I am running Ubuntu 14.04 server for Kiosk application. The problem is when kiosk is starting , kernel shows some debug messages about stuff like USB port error and such things, and those ugly ...
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1answer
132 views

Linux Server: Too Many Open Files

I have an application running on Linux Server. But server suddenly stopped responding but when I ping from other machine to server it allowed to ping but was not allowing to login into the server. Not ...
2
votes
1answer
150 views

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 ...
4
votes
2answers
482 views

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 ...
3
votes
4answers
1k views

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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0answers
277 views

Debian Jessie 8 idle on fresh install always a little too high, shows rcu_sched ksoftirqd kworker causing cpu load

Are the days of 0.0 cpu load on an "idle" server gone? I have another server (centos/redhat) 32GB ram that actually runs apache/MySQL/Lamp, mono, redmine/ruby, and other junk and its still shows me ...
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884 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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0answers
196 views

'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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2answers
339 views

Removing old kernels

My boot partition is full and I can't install new kernel versions. So I tried to remove some old versions like this: get active kernel uname -a Linux Ubuntu-1404-trusty-64-minimal ...
0
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1answer
295 views

NTP service stopped in centos7.1 linux machine

In our 3 linux boxes centos 7.1, we saw below messages in the logs and then ntpd service got stopped since the offset is more than 1000s. systemd: Time has been changed ntpd[2626]: 0.0.0.0 0617 07 ...
1
vote
1answer
165 views

How can I directly read data from a file in Linux without using the filesystem cache?

I have shared storage which is mounted (read-only) on SERVER1, and mounted (read-write) on SERVER2. SERVER2 is writing data to a file. SERVER1 is reading data from that file. The file poling is ...
0
votes
1answer
94 views

Write cache settings not working

I am using Debian 8.0 x64 with 72 GB of RAM with 4 drives configured as software RAID 0. Linux s1 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1 (2015-05-24) x86_64 GNU/Linux I tried setting dirty ...
2
votes
1answer
159 views

Can't get rid of mystery kernel

Just noticed that despite having the kernel updated regularly, the version in use is quite outdated: $ uname -a Linux test 2.6.31-302-rs #7 SMP Thu Oct 29 22:57:03 UTC 2009 x86_64 x86_64 x86_64 ...
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votes
4answers
499 views

When does an upgrade update the Ubuntu kernel?

I'm a little confused by Ubuntu/Linux kernel updates. Coming from a Windows background I sort of expect all updates to be available via the update manager, in the case of Ubuntu apt/aptitude. Yet if ...
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0answers
81 views

How to disable fibre channel LUNs entirely while doing an OS install?

SL 6.5 (aka RHEL 6.5) using a Qlogic adapter in a Dell R610. The module that is loaded is qla2xxx but also scsi_transport_fc. I have 2 SAS disks in RAID 1 for the OS and several FC LUNs for data ...
2
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3answers
2k views

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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0answers
177 views

Is transparent hugepage support on or off on these CoreOS machines?

I have a number of CoreOS servers that will be running some database workloads that highly recommend Transparent Hugepages be disabled. However: ~$ cat /sys/kernel/mm/transparent_hugepage/enabled ...
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164 views

Installing LTTng-modules 2.5.4 on CentOS 7

I am trying to install LTTng-modules 2.5.4 on CentOS 7, by building it from source because CentOS 7 is unable to install this package from RPM. Running "make" to build package contents results in the ...
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0answers
324 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 ...
0
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1answer
35 views

Linux kernel behavior when dealing with colliding subnets

I'm using openconnect to connect to my office VPN. They push some pretty crappy/aggressive routing rules allocating ALL of the private IP address spaces >.< After I connect to my office VPN, my ...
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2answers
2k views

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 ...
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0answers
40 views

How do processes stuck on uninterruptible sleep state get cleared upon reboot? [closed]

While processes stuck on an uninterruptible sleep state (i.e. TASK_UNINTERRUPTIBLE waiting I/O from a defunct device) cannot be killed by signals sent by root via the kill command, more often than not ...
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0answers
73 views

CPU usage of server extremely low and webpage load time high?

On a weekday at a time where very few use the optimized website on the server, the time for the page to completely load excluding 3rd party advertisements is about 0.6 seconds to 1 second. Now when a ...
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vote
2answers
39 views

Can I use kernel modules on Amazon HVM/PV instances?

It's a perfectly stupid idea, I know. But I want to test one of my older projects, which includes kernel module (Netfilter extension) on a virtualized cloud-y instance. Will it be possible for me to ...
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0answers
43 views

How to show per-process amount of non-swappable memory?

I am using a VPS which has, unfortunately, stringent limits on maximum total size of non-swappable memory for all processes in the container; this limit is called in kmemsize in OpenVZ. I would like ...