Questions tagged [sysctl]

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Kernel module for net.bridge.bridge-nf-call-iptables

This is on the Linux OS. I see that on some machines the net.bridge.bridge-nf-call-iptables variable doesn't exist until I modprobe the br_netfilter filter. I also see that there are some machines ...
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1answer
417 views

Sysctl parameter change after every reboot

I have found that the value of net.netfilter.nf_conntrack_count variable change every time i reboot the system. Did any one have an explanation for that?
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2answers
482 views

How can I configure system not respond to ICMPv6 echo requests sent to a broadcast address

I am attempting it by using echo command and it gives me the below error +++++++++++++ t040ml000002:/proc/sys/net/ipv4 # echo “1” > /proc/sys/net/ipv6/icmp_echo_ignore_all -bash: /proc/sys/net/...
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1answer
445 views

/etc/sysctl.conf Fedora {17-20}?

Since Fedora 16 or 17 there no longer file /etc/sysctl.conf. How do I setup net.ipv4.ip_forward = 1?
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1answer
597 views

How to undo kernel settings?

While trying to read some kernel parameters, I think I have mistakenly set some instead: # sysctl --system -r ^net.*tcp * Applying /usr/lib/sysctl.d/00-system.conf ... * Applying /usr/lib/sysctl.d/50-...
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123 views

do you have to restart services after running sysctl -p?

I'm increasing the watch limit on my RHEL 7 server and I'd like my changes to take effect without having to reboot. I've updated the /etc/sysctl.conf file so that the changes will be permanent. If I ...
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1answer
976 views

Default kernel parameters on new network namespaces

What are the default kernel parameters, when creating a new network namespace? Is there a way to override them upon creation? I think they are inherited by the parent process. An example using ...
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1answer
2k views

sysctl: malformed setting “net.ipv4.ip_local_reserved_ports=”

I'm trying to assign an empty string to a system setting, but it fails: [root@wc8rh7 ~]# sysctl -w net.ipv4.ip_local_reserved_ports="50000" net.ipv4.ip_local_reserved_ports = 50000 [root@wc8rh7 ~]# ...
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1answer
165 views

Kill process instead of panic on hung_task

There are sysctl parameters for hung_task* that allow you to emit error messages or panic if a process is in the D state for some amount of time. Is there anyway way to have the kernel kill the ...
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1answer
973 views

flashcache tuning

I installed flashcache version 3.1.1 and created a write-back cache. The performance is good as long as the percentage of dirty blocks is not too high. My application does heavy I/O at the beginning,...
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1answer
51 views

Is `vm.swapiness=0` equivalent to `swapoff -a` (in kernel >= 3.5)

Is setting in /etc/sysctl.conf: vm.swappiness=0 equivalent (except that it's persistent) to running swapoff -a, *in Linux kernels >= 3.5? *in earlier kernel versions, 0 meant 'no swapping until out ...
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158 views

What's the purpose of use_tempaddr=1 kernel parameter?

Reading sysctl docs, I found the following: use_tempaddr - INTEGER Preference for Privacy Extensions (RFC3041). <= 0 : disable Privacy Extensions == 1 : enable Privacy Extensions, ...
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1answer
1k views

Disable core file generation in RHEL7

I'm currently running RHEL7. I haven't been able to find a definitive explanation of how to disable core dump files. I can limit to number of core files that are produced, but I don't know how to ...
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298 views

Can't change kernel.printk value

I want to set kernel.printk value to 5 4 1 1 for disable logging on booting but when I try sysctl -w kernel.printk="5 4 1 1" I get error: sysctl: setting key "kernel.printk": Invalid argument ...
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0answers
68 views

write error for rmem_max on Angstrom

I am trying to tune the UDP receive and transmit buffer size. According to my real time application needs, I need to configure the Tx buffer as 6 bytes and Rx buffer as 22 bytes. I am running Angstrom ...
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126 views

sysctl IPv6 funtional defaults

ip-sysctl.txt: accept_ra_defrtr - BOOLEAN Learn default router in Router Advertisement. Functional default: enabled if accept_ra is enabled. disabled if ...
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480 views

linux sysctl tunable knob kernel.yama.ptrace_scope

The reference lists as values 0,1,2,3. Today I tried it on two servers : kernel 3.0.0 sysctl -w kernel.yama.ptrace_scope=3 error: "Invalid argument" setting key "kernel.yama.ptrace_scope" ...
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0answers
546 views

change TCP_TIMEWAIT_LEN at runtime

Linux kernel defines a timeout to destroy TIME-WAIT state of a connection in include/net/tcp.h: #define TCP_TIMEWAIT_LEN (60*HZ) Is there a way to change this parameter at runtime, via sysctl or /...
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740 views

Linux + kernel tuning parameters

I configured the following parametersbut after restart the values return to the previews values. How to configure them as permanent? echo 500 > /proc/sys/vm/dirty_expire_centisecs echo 3 > /...
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1answer
548 views

Why remount of /proc/sys is not global or does not persist in network namespace inside LXC

I have host running RHEL-7.2. Inside that running LXC. Inside LXC creating network namespaces. Inside the namespace changing sysctl variables was failing (as root): $ ip netns add testns $ ip netns ...
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291 views

Can you set Linux sysctl values at compile time

I am compiling a custom linux kernel. I want to set some sysctl values at kernel compile time. Defaults I want are different to the defaults kernel sets. Is there a way to do this? Please note I ...
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91 views

/etc/sysctl.conf abstraction for custom usage

Is there an abstraction model for configuration files like /etc/sysctl.conf ? I find it great for a few reasons, it's humanly readable, has nestable namespaces, hierachy of settings instead of one-...
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688 views

UDP buffer overrun and old datagram clearing

I am reading UDP datagrams on a linux server at 700,000 per second from HDL32 LIDAR system. Interface is ipv4. Sockets are set to SOREUSADDR. I turn on the LIDAR, start up socket program, it started ...
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1answer
1k views

Permission denied on aio-max-nr file

I would like to edit the file aio-max-nr: root@node:~# echo 65536 > /proc/sys/fs/aio-max-nr -su: /proc/sys/fs/aio-max-nr: Permission denied Knowing that : root@node:~# ls -lrth /proc/sys/fs/aio-...
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2answers
13k views

View current kernel parameters?

I saw in my syslog kernel.perf_event_max_sample_rate get changed. I was wondering if I could write a quick script to log this variable every few minutes. Currently it is: sysctl -a | grep kernel....
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Is -w option of sysctl really needed when changing kernel parameters?

sysctl has this -w switch. Is it really needed? I tried to do: sysctl vm.max_map_count=262144 And it seems to have worked out.
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1answer
75 views

How do I revert sudo sysctl -w kernel.unprivileged_userns_clone=1?

I did this in order to execute "brave browser" in my new debian installation. sudo sysctl -w kernel.unprivileged_userns_clone=1 I've read this maybe a potential risk for my machine security how do I ...
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1answer
800 views

Get a faster response for a ping

I noticed that the answer to my ping is slower in one debian machine that another. For the first one when i ping to 8.8.8.8: 64 bytes from 8.8.8.8: icmp_req=1 ttl=47 time=29.6 ms For the second ...
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93 views

Can't ping anything when IPV6 is disabled

When I disable IPV6 on my Debian install I can't reach the internet, and whenever I ping anything I get ping: unknown host ... This is how I am currently disabling IPV6 net.ipv6.conf.all....
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2answers
662 views

Open file handles

As I spawn several processes in a loop, I hit the maximum number of open files handles and the for loop breaks. When I count the open file handles using lsof I get: $ lsof | wc -l 1464377 However ...
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1answer
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sysctl -a doesn't include log_buf_len

I hope to check the value of log_buf_len via sysctl, but sysctl -a doesn't show it, why and is there any other way to check its value
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1answer
57 views

remove specific sysctl.conf setting

on some of my machines i have this block of setting in sysctl.conf(the numbers are different on each machine) : #Size Of RAM (In GB): 23 kernel.shmmni= 2547 kernel.shmmax= 365482458 kernel....
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1answer
261 views

Differences between forwarding and redirect in net.inet.ip

What are the differences between sysctl variables net.inet.ip.forwarding and net.inet.ip.redirect?
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1answer
79 views

linux + sysctl.conf configuration

Is it right to comment line with # in the file sysctl.conf? I ask because I am not sure if the comment lines would be read or not. more /etc/sysctl.conf #net.core.rmem_default = 1048576 #net.core....
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1answer
257 views

Change network values from sysctl.conf

Can I change the value of those parameters (spoofprotect, syncookies, dynaddr_hack, notimestamps, nobroadcasticmpecho, ip_forward) from sysctl.conf file in systemd?
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lsof show number of open files that are more then what configured [duplicate]

we verify the file max as [root@linux02 ~]# cat /proc/sys/fs/file-max 500000 but when we run lsof we get [root@linux02 ~]# lsof | wc -l lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/...
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18 views

cant counting all open files by lsof + lsof is hung

we are tying to count all open files by lsof lsof | wc -l lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/42/gvfs Output information may be incomplete. but sill after 1 hour ...
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77 views

Kernel parameter about max threads not being applied

I have manually edited /etc/sysctl.conf and added this line kernel.threads-max=70000 However despite the fact that # cat /etc/sysctl.conf | grep thread kernel.threads-max=70000 what I see is that ...
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1answer
45 views

oracle 11g installation on ubuntu 16.04 sysctl permission denied?

I am trying to install oracle 11g on ubuntu 16.04 after setting oracle 11g xe kernel parameters successfully # Oracle 11g XE kernel parameters fs.file-max=6815744 net.ipv4.ip_local_port_range=...
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1answer
155 views

Disabling all devices in /proc/acpi/wakeup permanently

In an effort to weed out an acpi problem, I need to set all the /proc/acpi/wakeup device variables to disabled. For the time being I'm doing it with acpitool and a script in /etc/rc.local ... usr/...
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1answer
179 views

how to turn off tcp timestamps?

I tried to turn off the tcp timestamp but it didn't work. The step i performed are the following: $ sysctl -w net.ipv4.tcp_timestamps=0 $ sysctl -p $ sysctl net.ipv4.tcp_timestamps (=> to be sure ...
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1answer
523 views

Enabling rp_filter loose (#2) mode for IPv6

does anyone have a solution to make reverse path filtering work (in loose mode) also for IPv6 and not only for IPv4? The setup I am having is a machine1 connected directly to a machine2, while ...
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0answers
423 views

How do I make my system only use swap when RAM is totally full?

In the past, setting vm.swappiness to 0 meant the system would only swap when RAM was totally full. $ cat /etc/sysctl.d/99-sysctl.conf kernel.sysrq = 1 vm.swappiness=0 $ sysctl vm.swappiness vm....
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1answer
1k views

ulimit value not changing for a process

We have a ruby application that started throwing lot of "unable to create new socket: Too many open files" errors recently I have updated "etc/security/limits.conf" as below root soft nofile ...
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1answer
407 views

Where is the __sysctl function defined in FreeBSD?

I am reading the source code to understand sysctl in FreeBSD. It looks like the most important function int __sysctl(const int *name, u_int namelen, void *oldp, size_t *oldlenp, const void *newp, ...