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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SYN Cookies on a LAN server - Ok / advisable to disable?

We are looking at tuning our linux tcp stack on one of our lan boxes. We were wondering if it is ok / advisable to disable SYN cookies on a server that doesnt have any sort of external (eg: "internet"...
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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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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 ...
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error: “net.ipv4.netfilter.ip_conntrack_max” is an unknown key

I have a problem on Ubuntu 10.04.3 LTS x64 with sysctl net.ipv4.netfilter.ip_conntrack_max . If I run this command on shell, I get back an error: error: net.ipv4.netfilter.ip_conntrack_max" is an ...
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No buffer space available and tuning with sysctl

Not really a network guy so please bear with me. I'm currently hosting a web application that sends UDP to all IP addresses in it's subnet periodically. That's 2048 IPs. My problem is it throws No ...
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Networking (dhcpcd) under LXC

I would like to boot an Arch Linux instance using LXC. Just about everything works, but I'm encountering the following error when trying to configure an interface using dhcpcd: # dhcpcd eth0 dhcpcd[...
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Linux networking port exhaustion

I've done as much research as I could on this without digging right off in the kernel source. There seems to be a large amount of disinformation/incorrect info on the subject, so I hope this answers ...
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After reboot debian box ignore sysctl.conf values

Where is right place for sysctl redefined values? I have: > uname -a Linux note 3.1.0-1-amd64 #1 SMP Tue Jan 10 05:01:58 UTC 2012 x86_64 GNU/Linux > cat /etc/debian_version wheezy/sid >...
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nf_conntrack: table full, dropping packet

Mar 24 03:29:26 kernel: [1557411.243821] TCP: time wait bucket table overflow (CT0) Mar 24 03:29:26 kernel: [1557411.243828] TCP: time wait bucket table overflow (CT0) Mar 24 03:29:26 kernel: [1557411....
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Xserve 10.6.8: Why do `net.inet.ip.forwarding` & `net.inet.ip.fw.enable` kernel sysctl settings stay enabled even disabling?

Very bizarre situation. I have inherited a few Xservers from a previous admin that I have been charged with cleaning up on various levels. I am familiar with settings in Ubuntu & am very ...
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sysctl -p /etc/sysctl.conf returns error

In a fresh installation of CenotOS 6 in a VPS after running sysctl -p /etc/sysctl.conf I got this errors: error: "net.bridge.bridge-nf-call-ip6tables" is an unknown key error: "net.bridge.bridge-nf-...
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Why change net.inet.tcp.tcbhashsize in FreeBSD?

In virtually every FreeBSD network tuning document I can find: # /boot/loader.conf net.inet.tcp.tcbhashsize=4096 This is usually paired with some unhelpful statement like "TCP control-block hash ...
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yum not updating /etc/rc.d/init.d/iptables

I have been hit by the bug https://bugzilla.redhat.com/show_bug.cgi?id=493226 (restarting iptables ignores values in /etc/sysctl.conf). This bug has been fixed by RH quite a while ago. The server ...
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Writeback cache in linux

In linux how do I have a writeback cache on disks? Basically, I'd like to setup a 100MB RAM cache for writing that writes out every 3-5 minutes or when full. Is this possible? Is there a sysctl ...
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Linux webhost security settings in /etc/sysctl.conf

While searching for more ways to secure Linux servers, I found the following /etc/sysctl.conf configuration. It came as is, without much explanation. Before using it on production environment (using ...
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What does tcp_orphan_retries set to 0 mean?

Does setting tcp_orphan_retries to 0 mean there is no limit to retries, or does it mean that it won't retry at all?
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Set sysctl.conf parameters with Puppet

This was a breeze in CFEngine... But I'm in a Puppet environment now, and need to be able to assign/ensure/check certain sysctl.conf variables. In the CFEngine world, I could simply check for specific ...
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ipv6 max_addresses in sysctl.conf (Debian 6)

I'd like to assign any number of IPv6 addresses to a Debian 6 host, but I see the following setting, and want to know what are the consquences of setting higher, or does this setting approach limits ...
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net.ipv6.conf.all.forwarding = 1 is an unknown key

I have few system with ipv6 addresses. I want to forward request from one system to another. hence I kept the option net.ipv6.conf.all.forwarding = 1 in sysctl.conf but the request is not getting ...
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sysctl.conf not running on boot

At what point is sysctl.conf supposed to be read during boot, and why might it not be running? I have the following settings which are not being applied when I reboot: net.bridge.bridge-nf-call-...
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sysctl setting for maximum connections from ip address

Is there any settings in sysctl that controls the maximum number of connections that are allowed from any one ip address? I'm having connection issues a redis server and a rabbitmq instance and I'd ...
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Optimize linux for serving http static content

What would be the system tunables to enhance serving static content? Like increase/decrease swappines, how to max out disk caching and so on...
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Tuning TCP sysctl on centos

I have website that gets higher tcp timeouts at peak times and slows down bit, here are few stat graphs http://i.stack.imgur.com/dgVyO.png sysctl config atm: net.ipv4.ip_forward = 0 net.ipv4.conf....
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How to make setting of kern.ipc.somaxconn persistent?

Want to rise value of kern.ipc.somaxconn With sysctl works ok $ sudo sysctl kern.ipc.somaxconn=2048 $ kern.ipc.somaxconn: 128 -> 2048 check it: $ sysctl -a|grep somaxconn kern.ipc.somaxconn:...