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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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Client TCP segments arrive in batches

The scenario is the following: a WebSocket server and clients exchange messages at some pace (like 40-50 times in a second). However, for one client, once in a few minutes I'm observing that there is a 5-second (always the same span) period, when…
tonso
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Problems with sysctl settings somaxconn

I'm trying to change the somaxconn settings, but for some reason they are not there. ***@***:~# cat /etc/debian_version bullseye/sid ***@***:~# uname -a Linux *** 5.4.78-2-pve #1 SMP PVE 5.4.78-2 (Thu, 03 Dec 2020 14:26:17 +0100) x86_64 x86_64…
unname
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Same sysctl kernel parameters for KVM host and guest

I need to set up a KVM guest with the following sysctl kernel parameters: net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 87380 16777216 net.ipv4.udp_rmem_min =…
dshykuts
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How to interpret the number of open and max file descriptors for nginx?

I want to get the currently open file descriptors and upper limit of open file descriptors on an AWS Linux instance. The reason is to determine whether to increase the limits for nginx to have enough file descriptors available. I get the following…
Manuel
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sysctl kernel core pattern not working with ~

I'm trying to put core dumps in home directory but for whatever reason a core pattern starting with ~ does not work while using full path works just fine. Can't seem to find this rule in docs. Not working, no core dumps generated: sysctl -w…
Andreas
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how are all/default/interface configuration influencing each other?

On the following kernel configuration path: /proc/sys/net/ipv6/conf/ we can configure each network interface in the following way: we can specify what configuration to follow for all interfaces we can provide a default configuration for any new…
Adelin
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File-descriptors setting on /etc/sysctl.conf

I have recently learnt that to be able to increase the amount of virtualhosts that we can serve via Apache depends on file-descriptors. they say the value should be added to /etc/sysctl.conf as fs.file-max = 65536 What is the correlation between…
Devrim
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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?
Ankur Agarwal
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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 output of sysctl -a, I didn't see any parameter…
user81604
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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 able connect anymore for some time (about 30…
parnas
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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 ? or for example when we do sysctl -w…
yael
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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…
Sam Alsalem
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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 my container, container's ipv6 is not disabled…
dawncold
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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 zabbix reports "nginx is down" with ping 0s. RPS at…
d.ansimov
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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. i did the following: i edit /etc/sysctl.conf and…
ufk
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