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Questions tagged [sysctl]

The tag has no usage guidance.

33
votes
2answers
9k views

What is the difference between “all”, “default” and “eth*” in /proc/sys/net/ipv[46]/conf/?

In sysctl, the /proc/sys/net/ipv[46]/conf/ keys have the following subkeys: all, default, and a key for each network interface. For example, on a machine with a single network interface eth0, it will ...
18
votes
2answers
22k views

Description of kernel.printk values

Between Debian 5 and 6, the default suggested value for kernel.printk in /etc/sysctl.conf was changed from kernel.printk = 4 4 1 7 to kernel.printk = 3 4 1 3. I understand that the first value ...
84
votes
4answers
96k views

How to persistently control maximum system resource consumption on Mac?

Before Mavericks, I could use /etc/launchd.conf file to change maximum system resource consumption, for example: limit maxfiles 16384 unlimited limit maxproc 16384 unlimited It no longer works in ...
6
votes
1answer
7k views

How to enable user_namespaces in the kernel? (For unprivileged `unshare`.)

My Linux kernel must have been configured with user_namespaces when built, but their use is restricted after boot and has to be explicitly enabled. Which sysctl should I use? (If this was turned on, ...
110
votes
6answers
95k views

Can I configure my Linux system for more aggressive file system caching?

I am neither concerned about RAM usage (as I've got enough) nor about losing data in case of an accidental shut-down (as my power is backed, the system is reliable and the data are not critical). But ...
61
votes
11answers
115k views

disable transparent hugepages

We are installing SAP HANA in a RAID machine. As part of the installation step, it is mentioned that, To disable the usage of transparent hugepages set the kernel settings at runtime with echo ...
3
votes
1answer
134 views

Writeback cache (`dirty`) seems to be limited below the expected threshold where throttling starts. What is it being limited by?

In a previous question and answer, I showed an experiment about dirty_ratio. Writeback cache (`dirty`) seems to be limited to even less than dirty_background_ratio. What is it being limited by? How ...
2
votes
1answer
303 views

Writeback cache (`dirty`) seems to be limited to even less than dirty_background_ratio. What is it being limited by? How is this limit calculated?

I have been testing Linux 4.18.16-200.fc28.x86_64. My system has 7.7G total RAM, according to free -h. I have default values for the vm.dirty* sysctl's. dirty_background_ratio is 10, and ...
10
votes
2answers
5k views

/proc/sys vs /sys/modules/mod/parameter

I've been wondering for last few days how exactly does it work. We can set kernel runtimes parameters using sysctl or echo boolen 1> /proc/sys/module/exactParameter but in /sys/modules/module/...
7
votes
1answer
1k views

Pernicious USB-stick stall problem. Reverting workaround fix?

There's an issue with Ubuntu that hasn't been fixed yet, where the PC freezes or gets really slow whenever it is copying to an USB stick (see Why is my PC freezing while I'm copying a file to a ...
4
votes
1answer
15k views

sysctl parameter for correct ARP response

I have a server that has some VMs, but the VMs can't communicate properly with the server because the server has several interfaces, and it responds on the wrong one. Q: We know that there is a ...
3
votes
1answer
5k views

cannot read key “net.ipv6.conf.all.stable_secret” in sysctl?

I am running kernel version as followings on an Arch Linux computer: [root@router ~ ]$ uname -a Linux router 4.2.5-1-ARCH #1 SMP PREEMPT Tue Oct 27 08:13:28 CET 2015 and I noticed that every time I ...
3
votes
2answers
2k views

Fedora /etc/sysctl.conf not loaded upon boot

I am running Fedora 27 with kernel 4.14.5 and have a problem that /etc/sysctl.conf is not being loaded upon boot. If I run: sudo sysctl -p after boot, my settings are loaded and everything works ...
2
votes
0answers
221 views

Is there an alternative for net.ipv6.ip_nonlocal_bind on FreeBSD?

On Linux (Kernel >= 4.3) I can "claim" an entire IPv6 subnet by routing it to localhost (sf#403648), and then by setting net.ipv6.ip_nonlocal_bind=1 so that I can bind on any of these addresses. I ...
1
vote
1answer
706 views

Restore part of a package that was accidentally deleted

In the process of trying to fix an issue, I accidentally deleted /sbin/sysctl when I was intending to delete /etc/sysctl.conf. When I run sysctl I get the error that says The program 'sysctl' is ...
1
vote
0answers
309 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....