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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.

Linux:
The sysctl command and configuration file use the /proc filesystem's sys directory to read information and apply changes.

The Linux Journal has an article about using sysctl, but most for the most complete information look to this description of /proc/sys's contents.

BSD-derived:
The sysctl command is used to read and configure certain system settings. The Handbook describes its general use in more detail, and the FreeBSD Performance Tuning Community Wiki has some ideas.

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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 second, everything seems to be OK. …
d.ansimov
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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 server uses 12 cores and NGINX is set to use 12…
M. Griffin
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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 Kernel Variables Loaded: loaded…
m1k3y02
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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 other devices are also connected, which means it is…
aloplop85
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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, we have tried two set of server: Setup A : only 1…
Chris
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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 = 14 But when I run the configuration using the…
Jay Bhatt
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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 performance hit. Requests that would normally take 400…
Will
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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 searched online but haven't found conclusive…
Mxx
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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[4213]: version 5.6.4 starting dhcpcd[4213]: eth0:…
larsks
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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 has had yum update run many times since the RH…
Jistanidiot
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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 like to eliminate this possible condition before…
Will Olbrys
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error: "net.netfilter.nf_conntrack_acct" is an unknown key

I have the this error when I run sysctl -p in Debian 5.0.8. error: "net.netfilter.nf_conntrack_acct" is an unknown key My sysctl configuration net.netfilter.nf_conntrack_acct = 1 net.ipv4.netfilter.ip_conntrack_max =…
anonymous
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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 sysctl config atm: net.ipv4.ip_forward = 0 net.ipv4.conf.default.rp_filter = 1 net.ipv4.conf.default.accept_source_route = 0 kernel.sysrq =…
Nick
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Automatic TCP SYN - cookie activation

I am simulating a SYN flood attack on a Raspberry Pi 1 with KALI Linux (ARM) installed. A similar message as mentioned in this post was printed after performing the attack: How to avoid syn cookies. kernel: possible SYN flooding on port X. Sending…
Gerry
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Can't disable Privacy Extensions for IPv6

On a fresh Debian 12 install, I wish to disable Privacy Extention for IPv6, but the config get rewritten every time I reboot. After doing the proper modification to /etc/sysctl.conf I'm getting the desired config: # /sbin/sysctl -a | grep…
sereizam
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