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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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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How to make sysctl network bridge settings persist after a reboot?

I am setting up a notebook for software demo purpose. The machine has 8GB RAM, a Core i7 Intel CPU, a 128GB SSD, and runs Ubuntu 12.04 LTS 64bit. The notebook is used as a KVM host and runs a few KVM ...
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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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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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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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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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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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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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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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What could cause system failure in sysctl and how to test values safely?

On AWS ec2, ubuntu t2.micro. I tried implement suggested improvements in sysctl listed here: https://gist.github.com/devster31/5900ab23b50a5a57f025#file-sysctl-conf and also added from other ...
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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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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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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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UFW - Set correct kernel params

As every system administrator does, one of the first things i did right after booting up my web server was install ufw and tune/set kernel parameters in /etc/sysctl.conf. By the way, this is my /etc/...
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systemd difference between start and restart

In /etc/sysctl.d folder we have config files are going to be applied at boot time. I use debian 8 with systemd. And now procps is managed by systemd. Please, help me understand, why service procps ...
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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 ...