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Questions tagged [sysctl]

sysctl is a mechanism for controlling options and limits in the Unix-like operating system kernels. Sysctls can be used to tune performance or change behaviors of many subsystems.

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error: “net.ipv6” is an unknown key

On one of my CentOS 6 machines I get $ sudo sysctl net.ipv6 error: "net.ipv6" is an unknown key Why do I see this and how can I fix this?
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162 views

Forwarding ipv6 traffic to localhost

I am trying to route HTTP/HTTPs requests from my computer running Linux Mint 18 to a proxy server listening on port 8080 on the same computer. I believe I have the configuration done correctly for ...
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2answers
312 views

sysctl -p /etc/sysctl.conf reverts to original settings after 1 minute

I need to tweak the kernel params as the Ubuntu minimal install is created for a machine with 256 MB of ram and our server has 32 GB. The issue I am having is that when I execute the command sysctl -...
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75 views

How does non-namespace specific sysctl variables work in the context of network namespaces?

Let's assume the systctl variables net.ipv4.tcp_wmem and net.ipv4.tcp_rmem. To my understanding, these variables can not be set per-namespace (but very soon apparently). My understanding is that ...
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1answer
53 views

seting rtprio limit in system without PAM

I have minimal linux system without PAM (custom complied linux based appliance) and I want to set system wide (all users) rtprio to 99. My idea is to do this with help of sysctl. But looking on ...
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471 views

Debian 8 - TCP Overflows / TCP Drops

I have recently installed netdata on my Debian 8 server (monitoring software) and afetr installing my Debian 8 server is reporting the below two alerts constantly. 1m ipv4 tcp listen overflows = 37 ...
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2k views

Sane value for net.ipv4.tcp_max_syn_backlog in sysctl.conf

I'm tuning sysctl.conf. According to an optimization guide on linode's website, the following is a sane value to set in sysctl.conf: net.ipv4.tcp_max_syn_backlog = 3240000 However, the same value ...
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2k views

How to get the count of open files by a user in linux

Is their any specific command or tool to get the count of open files by a user in linux?
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468 views

How can I reliably set net.core.ipv4.conf.rp_filter = 0 on CentOS 7?

I would like to disable reverse-path filtering on a CentOS 7 machine. I have a file in /etc/sysctl.d/ that contains the following in an attempt to disable it for all of my network interfaces: net....
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379 views

Reaching maximum TIME_WAIT sockets (tried tcp_fin_timeout)

tl;dr: How do i get the kernel to drop TIME_WAIT/closing sockets as forcibly and fast as possible? I don't care about data being lost since I'm not sending any. I'm currently running a little test ...
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1answer
114 views

What else can drop/delay connections, but iptables

In the office we have an interesting situation: after there is a connection (even if it's just a web page refresh) from any computer to our test server (hosted on AWS), another computer wouldn't be ...
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1answer
78 views

Fixing fs.file-max too small remotely

I was testing some things and breaking things in order to see if I could fix them. I was connected to a remote machine via Putty ssh and ended up changing fs.file-max to a very (comparatively) small ...
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1answer
848 views

What is the default maximum value for /proc/sys/kernel/shmmax

I am having an amiguity as to what the maximum value in shmmax should be set. After having a look at my system's statistics, it shows the following: #cat /proc/sys/kernel/shmmax ...
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2answers
140 views

/sbin/sysctl was overwritten accidentally , How do we restore it CentOS

We accidentally overwrote file /sbin/sysctl with command echo 1 > /sbin/sysctl How do we restore the file in centos?
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1answer
135 views

Default values on missing procfs and sysctl settings

I have several questions regarding the handling of procfs or sysctl values. Can a feature be enabled with a missing /proc file? Does a missing /proc or sysctl entry always mean that the option is ...
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1answer
326 views

linux + sysctl -a + from where sysctl -a print all kernel parameters

we have linux machine redhat 6 when we print all paramers from /etc/sysctl.conf we see only ~20 but when we perform sysctl -a we see more then 200 so from where sysctl -a print all these parameters ?...
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1answer
739 views

Centos7 disable IP Redirect sending on IPSec VPN Server

When using StrongSwan as an IPSEC S2S VPN Gateway, ICMP redirects are being sent to machines behind the right side. I have added the following lines to /etc/sysctl.conf: net.ipv4.conf.all....
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1answer
498 views

Why lxc container doesn't execute config files on /etc/sysctl.d?

My host is Ubuntu 16.04.1 LTS with privileged container. I want to disable ipv6 of container, so I created a config file on /etc/sysctl.d/60-disable-ipv6.conf, I have tried lxc-start and lxc-stop -r ...
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391 views

Debian sysctl config not persisting on reboot

I am running ubuntu 14.04: Linux WEBLB3 3.13.0-79-generic #123-Ubuntu SMP Fri Feb 19 14:27:58 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux I have modified the /etc/sysctl.conf file to set sysctl settings ...
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1answer
293 views

Cannot find default value in sysctl - Ubuntu

Im running Ubuntu 14.0.4 LTS and im trying to change some default values to optimize. I run sysctl -a to see all values. I have /etc/sysctl.conf and /etc/sysctl.d/ which has a few 10-*.conf files ...
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1answer
2k views

Overwhelmed by “TCP: time wait bucket table overflow” errors — What can I do to mitigate?

I've got a legacy system running Debian 7 (proxmox) hosting OpenVZ containers, and I'm seeing a troublesome problem where the system is being overwhelmed by open connections to VZ container running ...
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110 views

Unable to access Ubuntu EC2 ssh, Connection to Server-IP Closed

My server was having error due to high traffic and it showed this message often when I access the website Error: EMFILE: too many open files, open '/home/ubuntu/chat2/public/style.css' at Error (...
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2answers
3k views

Why isn't net.ipv4.tcp_rfc1337 enabled by default?

The tcp_rfc1337 setting seems to have a solution for TIME-WAIT Assassination. The first problem is that old duplicate data may be accepted erroneously in new connections, leading to the sent data ...
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1answer
144 views

Irresponsive nginx while doing “nginx reload”

While reloading nginx, I started getting errors in messages log "possible SYN flooding on port 443", and it seems like nginx becomes completely irresponsive at that time (quite for a while), cause ...
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1answer
371 views

SYN flooding on port 443 while nginx reload

While reloading nginx, I started getting errors in messages log "possible SYN flooding on port 443", and it seems like nginx becomes completely irresponsive at that time (quite for a while), cause ...
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0answers
83 views

running or building docker results in net.ipv4.ip_forward being reset

this is on a rhel6 system (docker 1.7.1 from epel). basically, everytime i do a build or a run, i can see that the net.ipv4.ip_forward sysctl gets reset to 0 - which results in the container loosing ...
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1answer
12k views

sysctl: cannot stat /proc/sys/net/ipv4/netfilter/ip_conntrack_max: No such file or directory

I try to change net.ipv4.netfilter.ip_conntrack_max by editing /etc/sysctl.conf net.ipv4.netfilter.ip_conntrack_max = 65535 and sysctl -p But i receive error: sysctl: cannot stat /proc/sys/net/...
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1answer
1k views

increase max_connections in mysql on ubuntu wily

I have ubuntu wily installed on my server. I'm trying to increase max_connections of mysql server to 1237 but when running mysql client and executing show variables like 'max_connections'; i get 214. ...
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1answer
654 views

Redis and Postgresql on same machine: vm.overcommit_memory=?

In the Redis documentation it clearly states that vm.overcommit_memory should be set to 1 to ensure background saving newer fails: http://redis.io/topics/faq HOWEVER In postgresql documentation it ...
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1answer
359 views

enabling ufw disables some of the settings in sysctl.conf

When I add rules to ufw and then enable it, some of my settings in sysctl.conf become void so I have to do sysctl -p after doing ufw enable. So for example one of my settings in sysctl.conf is to not ...
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75 views

nginx monitoring failed to load status page under load

Nginx monitoring script so-called ztc failing to load nginx test page (mostly under highest load to nginx about 2000 rps, which used as proxy), causing errors like "nginx is down" on zabbix, and, in a ...
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1answer
687 views

NGINX not responding during DDoS attacks

I'm going to get straight to the point, NGINX doesn't seem to handle any HTTP requests during a DDoS attack using XML-RPC. The server only uses about 1% of the CPU during an XML-RPC DDoS attack. The ...
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0answers
1k views

centos 7: sysctl -p /etc/sysctl.d/50-default.conf returns error

I have rented container from OVH a while ago but last night all of a sudden my machine stopped responding on IP level... after reboot I have noticed the following systemd-sysctl.service - Apply ...
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1answer
7k 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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3answers
1k views

OOM invoked with plenty of free swap

I am running an ARM router with i2p and tor on it - a Netgear R7000. Of course I've added a full 512 MB of SWAP to it to prevent OOMs, understanding that it could slow down the system... But then I ...
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1k views

Fast Ethernet UDP optimize receive buffers

I have a Linux computer which must receive streaming data from several devices (up to 30 or so) during long terms. This computer is connected to a Fast Ethernet local area network (100 Mbps) where ...
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4answers
12k views

Kernel Tuning with Privileged Docker Container

I'm building a container to tune kernel settings for a load balancer. I'd prefer to deploy those changes to the host in an image using a single privileged container. For example: docker run --rm --...
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1answer
572 views

Slow POST upload (Linux kernel Tuning)

I'm working in a Caucho Resin backend with an HAproxy configured in front of them, in a dedicated server. Now I'm dealing with a file upload problem. Our web application allows a file upload for ...
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2answers
4k views

Recommended TCP keepalive settings for a busy server

We are having some network timeout issues on a Debian server that is quite busy, and maintains multiple connections to a number of other servers on the network. Here are our current TCP keepalive ...
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1answer
53k views

How does vm.overcommit_memory work?

When I use the default settings: vm.overcommit_memory = 0 vm.overcommit_ratio = 50 I can read these values from /proc/meminfo file: CommitLimit: 2609604 kB Committed_AS: 1579976 kB But when ...
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3answers
6k views

Permission denied for root to change inotify max_user_watches, how solve this?

As root in a CentOs 6.4 server I got this error in an application: Fri May 16 01:45:23 2014 Error: Terminating since out of inotify watches. Consider increasing /proc/sys/fs/inotify/max_user_watches ...
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2answers
6k views

How to enable core files on CentOS 6

I am trying to enable core files on a machine running CentOS 6; however, nothing I have tried has produced core files…here is what I have done: Added the following two lines to /etc/security/...
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1answer
3k views

TCP Zero windows size and full windows size

The problem that we are facing is that some of the http connection have response time > 60s (about 5%). I discover that the problem should between the web server and loadbalancer. Here is my finding, ...
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1answer
3k views

TCP packet being retransmitted 7 times when sysctl tcp_retries1 is set to 3 - why?

Ubuntu 12.04 I am trying to better understand how many times TCP will attempt to retransmit a packet when it does not receive confirmation the destination received it. After reading the tcp man page ...
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104 views

How to learn max/min value of a sysctl parameter can be in FreeBSD?

I have a simple question. I want to learn max/min value of a sysctl parameter can be. Where can I find bounds of these parameters? Thanks
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1answer
409 views

How do you change tcp_congestion_control on OpenVZ?

I have a network of OpenVZ machines that I am testing various congestion control methods on. I need to know how to change the congestion control. Currently I get nothing but permission denied. Is it ...
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1answer
684 views

Permission denied when setting values in sysctl on Ubuntu 12.04

I am trying to configure my Ubuntu 12.04 VPS (OpenVZ) to reboot when it runs out of memory. To do this I have added following lines to my "/etc/sysctl.conf" file. vm.panic_on_oom = 1 kernel.panic = ...
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2answers
621 views

nginx or kernel queueing traffic

We have a setup that looks like this: nginx->haproxy->app servers We are terminating SSL with nginx and it sits in front of everything. During our peak load times, we are experiencing about a 2x ...
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2answers
2k views

Should rp_filter sysctl parameter be set on bonding master or member slaves?

I have a server running RHEL6.4. I need to configure .rp_filter sysctl parameter for my server's private interconnect. This server has 2 NICs bonded together. I looked through the documentation and ...
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1answer
108 views

available file handles is 0, how to increase [closed]

Since some days, we're getting "Too Many Open Files" within an Java application while loading files. So i start searching on Google, and increased fs.file-max to 200000 in my /etc/sysctl.conf. After ...