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Questions tagged [sysctl]

16 questions
2
votes
1 answer

Low `threads-max` on a debian installation

I have two different debian 10 installations, both with 4core/8GB-RAM (name them A and B). But the value of /proc/sys/kernel/threads-max is very different: A=63388 and B=7055. The value of threads-max should be total virtual memory / stack size [1].…
Taha Jahangir
  • 259
1
vote
2 answers

How to update Sysctl settings?

How to update Sysctl settings with fs.inotify.max_user_watches=1048576
spuggy
  • 121
1
vote
0 answers

How to disable IPv6 on a logical/vlan/sub interface?

On Linux CentOS7, sysctl fails disabling IPv6 on a logical/vlan/sub interface : $ ip -6 -o a show dev bond0.53 20: bond0.53 inet6 fe80::b283:feff:fee6:ba1/64 scope link \ valid_lft forever preferred_lft forever $ sudo sysctl -w…
SebMa
  • 2,035
1
vote
1 answer

kernel parameter - net.core.netdev_max_backlog , what happened when its too low

we want to understand what are the aspects when net.core.netdev_max_backlog kernel value is very low and not as recommended on our Linux RHEL machines , the value for this parameter is 1000 since our machines are HADOOP machines ( BIGDATA cluster…
King David
  • 1,001
1
vote
1 answer

How to set sysctl fs.notify.max_user_watches in GUIX? (guix system: error: service 'sysctl' provided more than once)

IDE's like PyCharm work better when fs.inotify.max_user_watches is set to a high level. How to do that in GUIX? I recall that the approach by Draketo used to work up to a few months ago: https://www.draketo.de/software/guix-config.html …
BlackShift
  • 739
1
vote
0 answers

Permission denied when systemd-sysctl service starts and tries to write to file in /proc/sys/user/

I am trying to enable user namespaces on Docker. This of course requires user namespaces to be enabled in the kernel. One of the steps to enable user namespaces in RHEL/CentOS is to: echo "user.max_user_namespaces=15000" >> /etc/sysctl.conf Because…
gfields
  • 11
0
votes
1 answer

vm.swappiness in /etc/sysctl.conf stopped working after updating to debain trixie/sid

Before the upgrade, I had Debian Bookworm with vm.swappiness=10 in my /etc/sysctl.conf, but after moving to trixie/sid cat /proc/sys/vm/swappiness started showing me 60 instead of 10. When I run sudo sysctl -p manually, /proc/sys/vm/swappiness gets…
Expie
  • 511
0
votes
1 answer

Is it possible to use ufw when kernel.modules_disabled=1

I am following Mastering Linux Security and Hardening 3rd ed. by Donald a. Tevault on Ubuntu 22.04 VPS. I have accepted suggested by lynis value 1 for kernel parameter kernel.modules_disabled, as recommended. $ sudo apt install lynis $ lynis audit…
legeyda
  • 3
0
votes
2 answers

linux + how to verify the dynamic ports allocation settings

How to know the range for the allocation of dynamic ports on red hat Linux machine From Linux we did sysctl -a | egrep "net.inet.ip.portrange.first|net.inet.ip.portrange.last" but those parameters are not in kernel configuration is that parameters…
King David
  • 1,001
0
votes
0 answers

Sysctl kernel boot parameter not always applied fast enough for dependent processes

I'm running Debian on a custom Chromium OS (cros) kernel on a Chromebook. Cros kernel has disk-based swap file disabled by default (since it prefers zram), and to enable it sysctl variable vm.disk_based_swap must be set to 1, otherwise mounting the…
seamux
  • 31
  • 1
  • 3
0
votes
0 answers

How to allow only 100 half open SYN connections

I'm running Ubuntu and want to allow only 100 waiting SYN connections at a given time, and drop the rest. How can I configure iptables to implement this rule? Or sysctl config to allow only 100, and drop the others
iTaMaR
  • 103
0
votes
0 answers

High CPU load on SYN flood

When being under SYN flood attack, my CPU reach to 100% in no time by the kernel proccess named ksoftirqd, I tried so many mitigations but none solve the problem. This is my sysctl configurations returned by the sysctl -p: net.ipv4.tcp_syncookies =…
iTaMaR
  • 103
0
votes
1 answer

How do I set /sys/block/X/queue/scheduler on Ubuntu 18.04 with HWE on startup

I am running Ubuntu 18.04 (Bionic) with the HWE stack installed. This means I have the 5.3 Linux kernel running. In older versions of the kernel, apparently passing elevator=noop when GRUB starts the Linux kernel would result in IO scheduling being…
Eric Urban
  • 204
0
votes
1 answer

Relationship of "ulimit -a" to fs.file-max

I am on an amazon linux ec2 instance and need to increase the files limit (to run spark). It had been my recollection there were a way to do something like ulimit -n 8192 But that is not "taking" ulimit -a still shows: open files …
WestCoastProjects
  • 4,032
0
votes
1 answer

`sysctl` not available in script started by swanctl on NixOS

I use strongswan-swanctl on a VPN server running NixOS. Basically it is working and I can connect to the VPN server from clients. services.strongswan-swanctl = { enable = true; …
Matthias Wimmer
  • 105
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