Questions tagged [kernel-parameters]

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Verifying Cold Reboot?

I noticed that I could do a "cold reboot" by setting kernel boot parameter reboot=cold. However, I wonder whether there is a way to verify that the reboot is indeed "cold". Thanks!
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System setting to stop WiFi from dropping connection?

My WiFi connection is frequently dropping. Are there any system settings to help with the problem?
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+50

MTRR (Memory Type Range Register) in Debian 10 dmesg messages

[Sun Mar 1 07:51:40 2020] MTRR default type: uncachable [Sun Mar 1 07:51:40 2020] MTRR fixed ranges enabled: [Sun Mar 1 07:51:40 2020] MTRR variable ranges enabled: [Sun Mar 1 07:51:40 2020] ...
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Use ISO9660 USB for booting

I'm trying to boot from a USB drive that has an ISO file dd'd onto it with dd if=file.iso of=/dev/sdb. The ISO file was created using grub2-mkrescue, and it boots about half the time if I specify root=...
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Network kernel command line (ip=) doesn't set the ip or route in Ubuntu 18 on Firecracker

I'm trying to launch a Firecracker VM with Ubuntu and set up networking. If I launch it regularly (taken from this repo): ./firectl --kernel=vmlinux --root-drive=image.ext4 --firecracker-binary=./...
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How to filter kernel parameter changes from kern.log?

I'm trying to add a use case to my SIEM where it triggers when kernel parameter change happen. I did some digging around the internet, but can't seems to find any method for filtering them from rest ...
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Controlling the page cache usage

The unfortunate situation that we're in right now is that historically, we've been over-provisioning RAM to our on-prem VMs and we're starting to run up to the limits of actual usage with midday ...
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Looking for dynamic kernel parameters from sysctl -a command

as title states, I'm looking to select both dynamic and fixed variables from sysctl -a command. Some parameters get changed every reboot? and I would like to have list of both dynamic and fixed. As I ...
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How to set sysctl using kernel command line parameter?

Is it possible to set Linux kernel sysctl settings (those usually set in /etc/sysctl.d) using kernel command line (those visible in /proc/cmdline)? (Using grub config file /etc/default/grub variable ...
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1answer
51 views

grub2-mkconfig not using /etc/default/grub?

I'm trying to add a kernel option "xxx" by adding it to the existing GRUB_CMDLINE_LINUX="xxxx crashkernel=auto rhgb quiet" line in /etc/default/grub, but after doing so, when I run grub2-mkconfig –...
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How to enable CMA in x86?

I tried to enable CMA in Ubuntu x86 as per the answer here. However meminfo still shows CMA as zero. We tried to give cma=8M@0-4G. Still it doesn't work. What would be the issue? Could you suggest a ...
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Can I use kernel parameter printk.time during boot to disable showing timestamps?

I am trying to use the kernel parameter printk.time in order to prevent showing timestamps in kernel messages logged in dmesg. According to this, it's possible to set printk.time=0 to disable the ...
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kernel.pid_max, kernel.threads-max, and ulimit -u

What are the differences of this? I am so confused. 1) If kernel.pid_max is the maximum number of PID that kernel can assign, then why is there a kernel.threads-max if there is already a kernel....
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1answer
214 views

GRUB: escape acpi_osi=“Windows 2015” in GRUB_CMDLINE_LINUX

How do I escape the string: acpi_osi="Windows 2015" To keep the space and quotes in GRUB's GRUB_CMDLINE_LINUX? [Alternate search term: acpi_osi=]
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1answer
350 views

How to change Kernel Base address when compiling Linux?

I am working on RedPitaya FPGA board and want to use Asymmetric MultiProcessing on it. CPU0 will be running Linux and CPU1 will be running Baremetal or freeRTOS. For that I need to change the Kernel ...
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Unable to mount Root File System without CONFIG_CGROUP in kernel - NFS or UBIFS same problem?

I am unable to mount a root file system, if I don't make the CONFIG_CGROUP=y in the kernel defconfig. Here is my bootlog Built 1 zonelists in Zone order, mobility grouping on. Total pages: 130048 ...
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2answers
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Compiling Linux kernel with all available drivers

I'm compiling the kernel for usage in portable USB stick. Which means it must run on any hardware, not just hardware of the machine where it is being compiled. What should I choose in kernel config ...
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Can I turn kernel params to make the network stack using swap instead of physical memory?

I'm doing a test about high-currency, and I only have a machine with limited memory. My goal is to setup more than 10M TCP connections on this memory limited machine. It seems that the network stack ...
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1answer
116 views

Addressing USB-Stick by UUID as kernel parameter in grub.cfg

I'm using Arch Linux and setting up an USB-Stick as decryption key for my luks-encrypted root partition (boot is unencrypted). I described it already in this question. Now, the key, that's used for ...
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195 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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How to configure embedded linux kernel so that the file system is visible on the host linux

I am using a powerpc, and after building and flashing the linux kernel on the device I can see the file system. But if I try to create a user or make any changes they get erased and resets to default ...
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1answer
375 views

boot parameters seems not to work with ipxe and daily image

I am trying to auto install debian buster with ipxe, it seems that the boot parameters don't work in the ipxe menu. I always get the language section. So the preseed isn't loaded. Here is the relevant ...
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370 views

Setting Kernel parameters when grub.cfg is on another distro

My setup is: -Windows 10 on a M.2 SSD -Ubuntu 18.04 on a normal ssd (sdb) -Arch Linux on sdb as well but on different partitions I first installed ubuntu with grub and later added arch linux ...
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557 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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How to disable retpoline?

I need to disable retpoline for a use case. I tried adding noretpoline to the boot parameter but it doesn't seem to work. The output after adding noretpoline param: $ cat /sys/devices/system/cpu/...
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1answer
1k views

Can no_console_suspend be set in runtime?

Is it possible to change this value in runtime without rebooting? I don't always have this problem, when I suspend right now I'm getting a failure and Suspending console(s) (use no_console_suspend ...
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1answer
907 views

lsmod 'used by' shows -1 while CONFIG_MODULE_UNLOAD=y

In this post there is some explanation about why does lsmod show -2 in 'used by' column. The idea is that the kernel config option CONFIG_MODULE_UNLOAD was not set. But what if lsmod shows -1 only ...
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173 views

Is Linux kernel parameters separated by space (0x20) or NUL (0x0)?

I thought it was NUL. But today when I wrote a script, I found that it was space. Is it configurable? Or just my memory wrong?
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453 views

How to specify multiple schedulers on the kernel boot command line?

We have systems with both spinning mechanical disks, and NVME storage. We want to reduce the CPU overhead for IO by taking any IO scheduler out of the way. We want to specify this on the Linux boot ...
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323 views

How to add VM kernel parameters in Qubes OS 4.0 ?

How to add sysrq_always_enabled and audit=0 kernel parameters to an AppVM in QubesOS 4.0 ? Current /proc/cmdline inside the VM is: [user@dev01-w-s-f-fdr28 ~]$ cat /proc/cmdline root=/dev/mapper/...
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1answer
813 views

How to ensure SysRq is always enabled regardless of the kernel.sysrq setting?

Some Linux distributions have kernel.sysrq=16 which means only Sysrq+s (sync) is allowed. As an example: Fedora (25 and 28) has it set as such in /usr/lib/sysctl.d/50-default.conf I had to create a ...
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161 views

Understanding workload sharing of readwrite in fio

I am exploring fio tools with different options. I want to share the read and write workload, so supplied below jobfile to fio. [read-4K-write-64K] blocksize=4K,64K, rw=readwrite rwmixread=50 size=...
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1answer
651 views

Linux Modify/Add Kernel Command Line from InitramFS “UserSpace”

I am developing an embedded Linux device. I have successfully created an InitramFS CPIO archive that runs quickly after boot. Now, I want to change the initial kernel command line to include "quiet" ...
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1answer
714 views

How does FIO benchmark set IOdepth?

NOTE: My question stems from this other U&L Q - What exactly is iodepth in fio? I want to know how internally FIO sets I/O depth. I.e., one of the parameters we submit to FIO when we run it is "...
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1answer
289 views

Kernel flags for exact architecture [closed]

I am using linux-libre-4.17.3. I want to switch off all unnecescary stuff like 'Amateur radio', Xen, Hyper-V, Wifi drivers that I am not using and so on... I think web search does not satisfy me. ...
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1answer
760 views

Kernel parameters are not changed permanently for RHEL7

Trying to permanently change some vm kernel parameters, I created /etc/sysctl.d/01-custom.conf config file as it described in Red Hat knowledgebase article. Here is its content: # cat /etc/sysctl.d/...
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Weird kernel.shmax value [duplicate]

I've noticed that kernel.shmmax value is set to oddly huge number on my RHEL 7 system. # sysctl kernel.shmmax kernel.shmmax = 18446744073692774399 Is it OK to have such a huge number set? How can ...
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31 views

Boot kernel parameter to run an executable at the end of booting, if found

Is there such a feature? The executable would be run if found after the usual boot time mounting. Preferably standard Unix filesystem path; for example, /root/autorun.sh, not (hd0,0)/root/autorun.sh. ...
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390 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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1answer
815 views

Difference between modprobe and sysctl -w in terms of setting system parameters?

We know that sysctl command can change kernel parameters with : # sysctl -w kernel.domainname="example.com" or by directly editing the file in /proc/sys directory. And for persistent changes, the ...
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1answer
783 views

ACPI kernel parameter options for HP ProLiant DL380 G5

Heavily related to a question on the sister site (https://serverfault.com/questions/874943/debian-9-black-screen-during-install), I have recently picked up an HP ProLiant DL380 G5 and attempted to ...
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1answer
988 views

How to increase atomic DMA coherent pool?

I recently attempted to compile a device driver (Xilinx XAPP1052) on Fedora Workstation 20. It gave me the following error. ERROR: 256 KiB atomic DMA coherent pool is too small! Please ...
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520 views

Why does the fs.inode-max kernel tunable not exist on version 2.6 of the Linux kernel?

The following output (from a Vagrant VM running CentOS 6.6) mostly speaks for itself: [root@localhost ~]# echo 131072 > /proc/sys/fs/inode-max -bash: /proc/sys/fs/inode-max: No such file or ...
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1answer
671 views

What does the Linux kernel do with unknown kernel parameters?

Supposedly I passed the kernel a parameter that it doesn't understand, for example blabla or eat=cake, what would the kernel do with these unknown parameters, the traditional case would be passing any ...
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585 views

Compile Kernel 3.10.107 for Ubuntu 16.04 LTS

Is there a good way to compile and use kernel 3.10.107 on Ubuntu 16:04 LTS? My main reason is that I have development/server machine where I want to add additional USB device what have drivers only ...
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can't mount on /proc/cmdline

I followed the this instructions in order to change the kernel boot args after boot: https://wiki.archlinux.org/index.php/kernel_parameters#Hijacking_cmdline I created /root/cmdline , but when ...
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672 views

How to get video mode given by hwinfo when it doesn't work? And how to set login resolution?

I tried to follow the suggestion at this previous post: Use sudo hwinfo --framebuffer as described, choose a video mode you would like to see during boot in console, then add the option vga=nnn to ...
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1answer
1k 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
4k views

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
2k views

LUKS password not being requested by dmcrypt / encrypt hook at boot

At boot I see: :: running hook [encrypt] A password is required to access the volume: Command requires device and mapped name as arguments Command requires device and mapped name as arguments ...