Questions tagged [devices]

devices refers to questions about the Unix/Linux device special files, normally these are under /dev. Do not use this tag for physical devices (for that use e.g. usb or pci).

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25 views

What is the utility and risk of the option -D in rsync --archive?

I use sudo rsync --archive --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*",/lost+found} a lot for ...
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Is It Possible/Advisable to Change Device USB Device Status from Terminal?

Running Pop_OS 20.10, I'm occasionally having problems with my headset not working after waking from sleep. The device is plugged in, and the issue persists even after switching from one USB to ...
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16 views

Using Udev Sound Device with ALSA

Inside of a C program, using libudev and libasound, I have determined a struct udev_device *device is part of the sound subsystem with udev_device_get_subsystem(device) == "sound". Now I ...
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Linux driver use, device and device file clarification

Need help filling in some knowledge gaps on driver use in user applications. I have a digital IO driver. I compile the driver and install it on boot with modprobe and when i check in /dev I can see /...
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How does Debian or Linux in general assign device-names like /dev/sdX on ZFS?

I have three identical servers, all three same cabeling and correctly placed hard-disk. Allthough one of the server got /dev/sdg /dev/sdh for the sata-ssds while the other two servers got them on /dev/...
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46 views

How can I mount /dev from C?

How can I mount /dev from C? I'm writing a simple init, and I know this sounds stupid but I would like to have /dev mounted to another folder. The manpages for mount() don't show dev as a supported ...
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1answer
28 views

From the Linux kernel's point of view, how does a user program communicate with a CUDA GPU?

I am curious about how data is copied back and forth between CPU and GPU memories when I run a CUDA program. Specifically, I want to know how the Linux kernel is involved in this process. I had a few ...
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1answer
37 views

How does Linux decide when to reuse USB minor device numbers?

When USB devices are connected in Linux the kernel assigns them a minor device number (i.e. the 0 in /dev/ttyUSB0). It seems that if I have a device at /dev/ttyUSB0, when I remove it and plug in a new ...
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29 views

Does device drivers use Kernel logical address space or Kernel virtual address space?

If possible, can you point to documentation or describe the kernel space memory layout? When a device driver instantiates a variable does that variable live in the kernel space or does it live in user ...
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13 views

Is there a reliable path to specific device events?

I'm running ubuntu linux and I have a bluetooth mouse that I would like to capture evdev events from. The problem is that the event device can potentially be different any time I connect the mouse: ...
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How can I backup a mount without a corresponding /dev special file?

Typically, I would just e.g. dd if=/dev/sda | gzip > backup.gz or something similar, but in this embedded device, I have a filesystem /dev/root on /rom type squashfs (ro,relatime) without a ...
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18 views

Dmesg ring buffer overload problem

I am writing a device driver. I need to seek in system logs; for that I use dmesg. In my case dmesg is overloaded with these warnings: [ 5578.052140] pcieport 0000:00:1c.5: AER: Corrected error ...
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100 views

Hide devices in chrooted environment

On Linux, I'm looking for a way to run grub-install <device> and update-grub in a chrooted environment without some devices being taken into account by GRUB (I don't want them to appear at boot)....
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28 views

How to mount device that appears in /proc/devices but not /dev?

I'm using a bare bones Linux distribution running on a Phytec i.MX6 ULL SoM on the Phytec demo board for this SoM. I need to be able to copy a file from an SD card. I flashed the SoM NAND from an SD ...
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USB device detection unreliable

I am running an Arch Linux and I have some issue with USB audio device detection on the running system. The detection works fine most of the time and is totally reliable on reboot, but especially when ...
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second bluetooth device on debian

I have debian xfce plus nomfree drivers installed, have a bluetooth keyboard installed and its working, where I use bluetoothctl to connect it, if I try to connect a second device like a bluetooth ...
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Why can't I read /dev/disk0 in macOS as root?

I am trying to read the partition table of my startup disk manually. I open sudo python and issue f=open('/dev/disk0', 'r'). What happens is that I get PermissionError: [Errno 1] Operation not ...
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33 views

copy files from the folder on one disk to the folder on another disk

how to copy files from the folder on one disk to the folder on another disk use cp command? (from the current directory on sda2 to folder on /dev/sdb3?)
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1answer
47 views

Mounting encrypted SD card: where does /dev/dm-3 come from?

I was trying to mount an encrypted SD card on Kubuntu 20.04. lsblk gives me this: NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT loop0 ...
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1answer
26 views

How to convert stream data which come over udp to video device?

I'm trying to share my computer's camera with the remote computer. In order to do this, I wanted to share my own computer's camera with the udp port(stream), take the stream on the remote computer and ...
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1answer
80 views

udev rule for wacom tablet that has changing IDs

I had a lot of trouble trying to configure the buttons on my wacom tablet on a manjaro installation. I ended up using this answer to actually get it working, but it only worked some of the time ...
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99 views

Why does PulseAudio open all ALSA sound devices when it starts?

See also How does PulseAudio start?. When the PulseAudio audio daemon starts, it by default loads module-udev-detect, which detects and opens all of my sound cards. PulseAudio uses ALSA to interface ...
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806 views

Why created directories disappearing after reboot in /dev?

I'm new to Linux. When I try to create a directory in /dev folder it's happening smoothly but after rebooting all created folders are disappearing. I tried in other folder like /etc, everywhere ...
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Writing to a device hangs, how can I troubleshoot this?

I have a teensy 3.6 as /dev/ttyACM0 I noticed that when I used serial.write() in python it would hang. I opened the Arduino IDE serial monitor and I can see the output. When I write in the serial ...
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Could a new AMD processor be limiting dd write speed when using /dev/urandom as the input?

I have recently bought a new computer that uses a pretty recent AMD Athlon chip. When using it for low-level formatting with dd, I noticed that setting if=/dev/zero allows it to write to the disk at ...
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Setting USB Hub device authorized flag to 1 does not work

I have a USB Hub listed under /sys/bus/usb/devices as 1-2. It's the only device issuing echo 1 > /sys/bus/usb/devices/{device} does not work (returns bash: echo: write error: Invalid argument). ...
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31 views

How can I find a drive specified by a ID_VENDOR_ID:ID_MODEL_ID more easily?

I'm using virt-manager and I am trying to select a USB device. It's telling me some valuable device information: but I don't know where to find that other than using: udevadm info --query=all --name=/...
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292 views

where can I find socket files? ( I want unlink it and remove it..)

I'm doing debugging for a program that uses UDP socket. The program creates a socket but after that due to some other problems the program gets stuck and I cannot kill it properly. So I close the ...
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77 views

Ubuntu keeps scrolling down and typing '~' on its own

For awhile now, while using my laptop running Ubuntu, it will constantly scroll down to the bottom of the page even while I'm trying to move up. It also will sometimes constantly type ~! I've tried ...
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46 views

Best practice to deal with group permission on device shared with docker container

I have a Docker container from which I want to play sound. The container is alpine based, the host is debian based. I try to follow the 'best practice' of not running with root in the container (in ...
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1answer
190 views

Is it necessary to mount devtmpfs with /etc/fstab?

I'm working on a Linux-like operating system for aarch64, based on a 5.6.4-v8+ kernel for Raspberry Pi 3 (Model B+). The Kernel configuration options include: CONFIG_DEVTMPFS=y CONFIG_DEVTMPFS_MOUNT=y ...
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1answer
73 views

What is the meaning of `ATTR{stat}==“ …”` on udev attributes?

I was studying about the activity/change while copy pasting file in USB. Seems like the stat attribute gets changed on every action on USB drive. So what does each value of these stat denotes? Command ...
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1answer
107 views

Trying to run linux kernel using QEMU, having trouble with boot process

For a project, I need to be able to run an uncompressed linux kernel. It was recommended to me to try emulating this using QEMU, since that's less involved than booting it straight on the machine. ...
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Keeping LCD backlight On while going in sleep state

i am using ubuntu 18.04.4 and i am trying to use some power management related stuff. I want to keep laptop backlight ON (using sysfs) while my laptop is entering into sleep, i am giving following ...
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1answer
48 views

Can't locate USB devices

I'm currently playing with USB to learn more about it. I used lsusb to display infos about USB buses and devices of my system. Knowing that basically everything is either a file of a directory on ...
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1answer
50 views

Does a Linux block special file have a corresponding character special file

Simple codger question from the days of UNIX... Does Linux have character special files which correspond directly to a block special file? Back in my day 👴🏻 each disk in UNIX had both a block ...
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26 views

How does the kernel interacts with drivers and device tree?

I have an embedded linux system running on a board. I had, in the device tree, the uart device, and also a driver for that. In that case, after boot, I could see a /dev/ttymxc0 "file" in the ...
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2k views

What is swap priority and why does it matter

While seeing the manual for swapon command the priorty option is described as -p, --priority priority Specify the priority of the swap device. priority is a value ...
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1answer
176 views

Cannot communicate with USB device in Linux

I hope someone can help me with this one. I am trying to connect a spectrometer device (ThorLabs vendor) via a USB interface in a Linux environment (I am using openSUSE 15.1). However, this ...
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1answer
121 views

Permanently grant permission to /dev/snd for all users?

After reboot ~$ arecord -l arecord: device_list:270: no soundcards found... and $ sudo arecord -l **** List of CAPTURE Hardware Devices **** Home directory not accessible: Permission denied card 0: ...
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190 views

My USB controller is not recognized (error 10) when I try to pass through it in a Windows 10 guest os with virt-manager and a QEMU-KVM vm

Actually I have a problem to fix. I want to attach two Kinect 2,one for each virtual machine with its own USB controller and GPU using virt-manager with a QEMU-KVM connection on Ubuntu 20.04. The ...
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1answer
97 views

Get major and minor from path's s

To get the major and minor device numbers a device node corresponds to, you use stat -c %T:%t <device file> To get the device number that a path is on, you use stat -c <%D|%d> <path>...
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55 views

“pkgProblem” error, can't install package

I have some problems while installing a package with apt (like gdb). Here is the error I am getting: The following packages contain unsatisfied dependencies : linux-headers-5.4.0-kali2-amd64 : ...
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1answer
104 views

device names in rfkill output do not match those from ip

The devices listed by the rfkill command are completely different from the device names listed by the ip command: > rfkill ID TYPE DEVICE SOFT HARD 0 wwan tpacpi_wwan_sw ...
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1answer
223 views

How does an open(at) syscall result in a file being written to disk?

I'm trying to learn as as much as I can about about the interplay between syscalls, the VFS, device driver handling and ultimately, having the end device do some operation. I thought I would look at a ...
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848 views

Reading from dev/urandom - system behaviour

When reading from dev/urandom, with say head or dd, it’s of course expected that the output is always random and different. How is this handled by UNIX at a low level? Is the file naturally truncated ...
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39 views

How do I troubleshoot my sd card reader?

My card reader doesn't seem to be able to recognise, let alone read, anything any more. lspci -v lists the device: 06:00.0 SD Host controller: O2 Micro, Inc. SD/MMC Card Reader Controller (rev 01) (...
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3answers
362 views

SATA disk drive behind Adaptec RAID 5405 can't be detected as block device

Due to shortage of free built-in SATA 3.0 plugs (6 totally) on my motherboard (Gigabyte 970A-DS3 rev.3) I've got an Adaptec RAID 5405 (3G SAS/SATA RAID) to move all "slow" SATA 1.0/2.0 ...
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1answer
966 views

cfdisk: cannot open /dev/sda

Background Info I am currently trying to build a Linux From Scratch (LFS) partition. This is my first attempt and I'm doing this to challenge myself, but I'm having trouble getting started. I'm using ...
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1answer
225 views

How does the i2c subsystem match devices against drivers?

My understanding of this is fairly minimal so bear with me. From what I gather so far, the i2c subsystem on Linux identifies devices that are attached, and then matches them against loaded driver ...

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