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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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73 votes
3 answers
68k views

Understanding /dev and its subdirs and files

$ ls -l /dev/stdin /dev/fd/0 lrwx------ 1 tim tim 64 2011-08-07 09:53 /dev/fd/0 -> /dev/pts/2 lrwxrwxrwx 1 root root 15 2011-08-06 08:14 /dev/stdin -> /proc/self/fd/0 $ ls -l /dev/pts/2 /proc/...
Tim's user avatar
  • 102k
16 votes
1 answer
46k views

Is there a way to change device names in /dev directory?

I wrote this rule for testing purpose: SUBSYSTEMS=="usb", ATTRS{manufacturer}=="Kingston", ATTRS{serial}=="001CC0EC34A2BB318709004B", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1642", SYMLINK+="pen",...
Mikhail Morfikov's user avatar
107 votes
3 answers
143k views

What is stored in /dev/pts files and can we open them?

According to my knowledge, /dev/pts files are created for ssh or telnet sessions.
user2720323's user avatar
  • 3,589
287 votes
16 answers
1.2m views

How do I find out what hard disks are in the system?

I need to know what hard disks are available, including ones that aren't mounted and possibly aren't formatted. I can't find them in dmesg or /var/log/messages (too much to scroll through). I'm hoping ...
xenoterracide's user avatar
109 votes
3 answers
135k views

What are character special and block special files in a unix system? [duplicate]

How are character special files and block special files different from regular files in a Unix-like system? Why are they called “character special” and “block special” respectively?
Geek's user avatar
  • 6,738
171 votes
3 answers
159k views

When to use /dev/random vs /dev/urandom

Should I use /dev/random or /dev/urandom? In which situations would I prefer one over the other?
Tom Hale's user avatar
  • 30.8k
92 votes
4 answers
38k views

Why are network interfaces not in /dev like other devices?

I'm mostly curious, but why aren't network interfaces in /dev? Are there any other kinds of devices that aren't represented as a node under /dev?
andyortlieb's user avatar
  • 1,021
13 votes
3 answers
13k views

Call notify-send from an udev rule

I use Linux Mint 13 MATE, and I'm trying to set up notifications when I plug/unplug devices. First of all, I found udev-notify package, but unfortunately it almost doesn't work for me: it works for ...
Dmitry Frank's user avatar
  • 2,748
34 votes
2 answers
24k views

What’s the difference between a “raw” and a “cooked” device driver?

Does this concept only apply to terminal drivers (which is what most sites cover) or to any driver in general?
soc's user avatar
  • 450
12 votes
1 answer
8k views

Why do my SATA devices show up under /proc/scsi/scsi?

I have 3 SATA devices on my system. They show up under /proc/scsi/scsi, although these are not SCSI devices. Why do my SATA devices show up under the SCSI directory? $ cat /proc/scsi/scsi Attached ...
Stefan Lasiewski's user avatar
71 votes
3 answers
46k views

How to create /dev/null?

I deleted my /dev/null. How can I restore it?
LanceBaynes's user avatar
  • 40.4k
33 votes
2 answers
23k views

Multiple /dev/video for one physical device

First some specs: my computer is an HP EliteBook 8460p. It comes with an integrated Chicony HP HD webcam. My issue is that a lot of applications (well, at least Skype and guvcview) are displaying ...
kagmole's user avatar
  • 453
47 votes
4 answers
161k views

How to Reset/Cycle Power to a PCIe Device?

I have a PCIe device that only works correctly when the computer is fully powered off then on again. Issuing a simple reboot or reboot -p command does not appear to cycle the power to the PCIe card, ...
zachd1_618's user avatar
26 votes
1 answer
20k views

Why is "nodev" in /etc/fstab so important? How can character devices be used for hacking?

I am learning about linux security and struggling to understand why a USB stick with a character device on it is potentially dangerous. If I have a USB stick with a bash executable that has setuid ...
rosix's user avatar
  • 1,043
23 votes
8 answers
4k views

How can I put a bit mask on /dev/zero so that I can get bytes other than zero?

How can I put a bit mask on /dev/zero so that I can have a source not only for 0x00 but also for any byte between 0x01 and 0xFF?
Eduard Florinescu's user avatar
10 votes
1 answer
24k views

Understand output of `udevadm info -a -n /dev/sdb`

I plug an external HDD into my laptop. I try to find out the information by $ udevadm info -a -n /dev/sdb Udevadm info starts with the device specified by the devpath and then walks up the chain of ...
Tim's user avatar
  • 102k
6 votes
3 answers
2k views

How to get my USB key to auto mount

I'm currently working in a command line only environment. When I plug my USB key in, I see a new device file in /dev: ... sdi sdi1 ... If I simply sudo mount /dev/sdi1 /media/tmp, and umount it ...
nopcorn's user avatar
  • 9,609
4 votes
2 answers
7k views

sysfs and devtmpfs

Ulrich Dangel explains very well the difference between devtmpfs and udev. What about sysfs? I understand that the kernel uses sysfs to export device nodes to user space to be used by udev. So ...
Daniel's user avatar
  • 41
117 votes
9 answers
26k views

Why is /dev/null a file? Why isn't its function implemented as a simple program?

I am trying to understanding the concept of special files on Linux. However, having a special file in /dev seems plain silly when its function could be implemented by a handful of lines in C to my ...
Ankur S's user avatar
  • 1,218
19 votes
3 answers
49k views

How to grant non-root user access to device files

I have device file that appears in /dev when a specific board is plugged in. The read and write operations to it work just fine, but in order to open the device file the program needs to be executed ...
sj755's user avatar
  • 1,125
17 votes
1 answer
3k views

Does Posix require any devices?

Does Posix require any devices? For example, /dev/urandom, /dev/zero or /dev/null? I suspect not because of non-*nix OSes, but wanted to ask for completeness.
user avatar
16 votes
4 answers
4k views

Trouble with understanding the concept of mounting

Having read both What is meant by mounting a device in Linux? and understanding "mount" as a concept in the OS, I have a problem where it is stated that All accessible storage must have ...
sounak's user avatar
  • 501
14 votes
4 answers
7k views

If I connect a physical device, how can I ever know which device file belongs to it?

Say I plug in several USB drives which don't get automatically mounted. How can I find out which device file belongs to which physical device, so I can mount it for example? I'm running Mac OS X but ...
user avatar
13 votes
2 answers
25k views

wlan number assignment

How or where does Linux determine the assignment of a network device? Specifically, wlan0 or wlan1 for wireless USB devices. I plugged in a TP USB wireless a while ago, and it was assigned wlan0. I ...
Huntrods's user avatar
  • 233
7 votes
3 answers
17k views

Creating eth0 with consistent network device naming

From my understanding, Arch Linux uses Consistent Network Device Naming where the network devices are no longer named eth0, eth1, etc. I use the proprietary MATLAB software which requires a device ...
StrongBad's user avatar
  • 5,291
6 votes
3 answers
9k views

Can I share a device from under /dev across hosts?

Here's the situation. I have a video device /dev/video0 on a VMware Server and I want to access this device from within a virtual machine. However for whatever reason I can't connect the device ...
Josh's user avatar
  • 8,468
6 votes
3 answers
19k views

RHEL: Creating stable names for network interfaces

We have a RHEL 5.5 box with 8 interfaces. And the eth interface naming is flip flopping. Sometimes eth0 comes up on physical port 7th, and sometimes on another physical port. We want the naming to ...
user1263746's user avatar
2 votes
2 answers
7k views

Blacklisting / Removing driver for a particular VID/PID

This is in continuation of my previous problem. Accessing a USB device under Non - Privilaged user with FTDI2XX Driver Here i have 2 usbserial hardware modules and it is provisionised that only one ...
Ragav's user avatar
  • 421
128 votes
7 answers
67k views

How are "/dev" Linux files created?

There are special files in Linux that are not really files. The most notable and clear examples of these are in the dev folder, "files" like: /dev/null - Ignores anything you write to the file /dev/...
IQAndreas's user avatar
  • 10.4k
82 votes
9 answers
31k views

Why do we need to mount on Linux?

I understand what mounting is in Linux, and I understand device files. However I do not understand WHY we need to mount. For example, as explained in the accepted answer of this question, using this ...
Greeso's user avatar
  • 923
43 votes
2 answers
27k views

What are nvme namespaces? How do they work?

I've recently begun supporting Linux installed on devices with built-in nvme ssds. I noticed the device files had an extra number, beyond a number identifying the drive number and the partition number....
JeffFromOhio's user avatar
35 votes
1 answer
58k views

using devtmpfs for /dev

I have noticed the following option in the kernel: CONFIG_DEVTMPFS Device Drivers -> Generic Driver Options -> Maintain devtmpfs to mount at /dev And I see that it is enabled by default in the ...
user1968963's user avatar
  • 4,093
33 votes
2 answers
40k views

How do mouse events work in linux?

This is mostly out of curiosity, I'm trying to understand how event handling works on a low level, so please don't reference me to a software that'll do it for me. If for example I want to write a ...
fiftyeight's user avatar
32 votes
2 answers
18k views

Difference between /dev and /sys

Exactly what is the difference between devfs and sysfs? Both seem to maintain a list of hardwares attached to the system. Then why the need for 2 separate fs even arose? As far as I can get /sys ...
sounak's user avatar
  • 501
30 votes
3 answers
61k views

Mounting a device — role of /dev, /media and /mnt, and the mount command [closed]

I have several closely related questions about what happens when I insert a CD. The files on the CD /media/Ubuntu\ 11.04\ i386/, but from what I've seen /dev/cdrom is also involved. What is the ...
Tim's user avatar
  • 102k
26 votes
2 answers
18k views

How does /dev/fd relate to /proc/self/fd/?

$ ls -l /dev/stdin /dev/fd/0 lrwx------ 1 tim tim 64 2011-08-07 09:53 /dev/fd/0 -> /dev/pts/2 lrwxrwxrwx 1 root root 15 2011-08-06 08:14 /dev/stdin -> /proc/self/fd/0 $ ls -l /dev/pts/2 /proc/...
Tim's user avatar
  • 102k
23 votes
6 answers
55k views

How can I tell whether a network interface is physical (device) or virtual (alias)?

I have a small home router running OpenWrt (Kind of embedded Linux for routers). It has five Ethernet ports, one labeled WAN and four labeld LAN 1 to 4. It has the following Network Interfaces defined ...
Lumi's user avatar
  • 762
21 votes
2 answers
31k views

What causes /dev/disk/by-label to be populated?

I've noticed that Linux distributions typically have a /dev/disk/by-label directory, but this isn't always the case (For example, the CirrOS Linux test image doesn't have one). What's required on a ...
Lorin Hochstein's user avatar
20 votes
4 answers
87k views

PKCS#7 signature not signed with a trusted key

Installed Ubuntu with SIP disabled on MacBook 2017 - 0 issues, booted in seconds. I have been building it out and created a problem while trying to make the WiFi work. At some point (it was very late)...
Earthling's user avatar
  • 201
19 votes
5 answers
16k views

Are there alternatives to using `udev`?

While I understand the greatness of udev and appreciate the developers' effort, I was simply wondering if there is an alternative to it. For instance, I might imagine there should be a way to make ...
humanityANDpeace's user avatar
16 votes
2 answers
8k views

Why are there so many virtual terminal devices?

I've been reading the Advanced Linux Programming book and it mentions about virtual terminals which, if I understood it correctly, it is a Linux-specific feature (not in Unix) to allow multiple login ...
ArmenB's user avatar
  • 325
16 votes
4 answers
18k views

Can I setup a loopback audio device?

If I can send audio to the output devices, then I can record the same audio as a wave. With filesystems, you can just setup a loopback filesystem and write binary data on a file instead of a device. ...
D4RIO's user avatar
  • 1,576
16 votes
5 answers
19k views

Special File that causes I/O error

I want to automatically test if a piece of software reacts as expected if an essential SQLite DB file fails to be read (causing an I/O error). Exactly that happened some days ago at a client. We ...
mreithub's user avatar
  • 3,623
13 votes
2 answers
6k views

Can I stop Linux from listening to a USB input device as a keyboard, but still capture events with a program?

I have a USB barcode scanner at /dev/input/event0 (/dev/input/by-id/usb-Metrologic_Metrologic_Scanner-event-kbd), and scanning a barcode causes it to send keypress events. I'm capturing these ...
ndbroadbent's user avatar
12 votes
2 answers
151k views

/dev/sdb: No such file or directory (but /dev/sdb1 etc. exists)

I'm not sure what is wrong here but when running fdisk -l I don't get an output, and when running fdisk /dev/sdb # I get this fdisk: unable to open /dev/sdb: No such file or directory I'm ...
Goulash's user avatar
  • 574
11 votes
2 answers
36k views

Allow non-root user to read/write /dev files

In my /dev folder, I would like the following files to be user readable and writable: /dev/ttyUSB0 /dev/gpib0 How do I do this without using chgrp? I can edit /etc/udev/rules.d but I do not know the ...
Kit's user avatar
  • 1,053
10 votes
5 answers
6k views

Why doesn't xsetwacom work from udev?

I made a script to rotate my Wacom Bamboo tablet 180 degrees. It works fine when I execute it as myself (user) or root, but when started from udev (i.e. when plugging the tablet into a usb port) it ...
Redsandro's user avatar
  • 891
8 votes
2 answers
12k views

How Linux uses /dev/tty and /dev/tty0

I can see the difference between /dev/tty and /dev/tty0 by testing the provided method from this question. But I really wonder about the practical usage of those devices (like situations they will be ...
Ron Vince's user avatar
  • 1,442
7 votes
1 answer
4k views

How to be notified when a USB device was plugged in?

My system has to auto-mount USB devices; how can I be notified when a USB device is plugged in? Where can I read more about this subject? I would like to handle this problem via C or a shell script.
The Student's user avatar
  • 3,569
7 votes
2 answers
18k views

Prevent usbhid from claiming USB device

Directly related: Prevent claiming of novelty usb device by usbhid so I can control it with libusb? I want to access an RFID reader (works as HID device) from a program that uses libusb-0.1. In the ...
AndiDog's user avatar
  • 241