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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).

48
votes
3answers
43k 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/...
12
votes
1answer
26k 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",...
69
votes
3answers
78k 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.
217
votes
14answers
849k 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 ...
67
votes
4answers
21k 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?
63
votes
3answers
79k 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?
13
votes
2answers
9k 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 ...
62
votes
3answers
52k 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?
9
votes
1answer
6k 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 ...
13
votes
4answers
2k 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 ...
20
votes
8answers
3k 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?
6
votes
3answers
1k 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 ...
66
votes
9answers
21k 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 ...
114
votes
9answers
20k 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 ...
60
votes
2answers
28k views

How to create /dev/null?

I deleted my /dev/null. How can I restore it?
13
votes
4answers
6k 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 ...
17
votes
1answer
8k 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 ...
11
votes
2answers
22k 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 ...
9
votes
1answer
1k 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.
6
votes
3answers
17k 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 ...
2
votes
2answers
2k 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 ...
22
votes
2answers
26k 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 ...
15
votes
4answers
34k 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 ...
16
votes
3answers
32k 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 ...
11
votes
2answers
4k 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 ...
3
votes
2answers
4k 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 ...
15
votes
4answers
12k 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. ...
15
votes
4answers
8k 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 ...
8
votes
2answers
7k 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 ...
22
votes
2answers
13k 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?
11
votes
1answer
19k 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 ...
16
votes
3answers
29k 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 ...
12
votes
5answers
10k 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 ...
6
votes
3answers
11k 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 ...
12
votes
2answers
35k 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)...
5
votes
1answer
1k views

How to disable USB devices based on their vendor ID on GNU/Linux?

In that question someone wanted a blacklist for all USB devices, and then only allow specific devices. In this question, we want to accept all USB devices, but prevent the driver (e.g. cdc_acm) from ...
11
votes
2answers
4k 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 ...
6
votes
1answer
2k 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.
2
votes
1answer
4k views

What's the difference between 'no caching page mode present' and 'assuming drive cache. write through.'

Post-POST, post-BIOS screen, post-GRUB; when I boot Debian with a SD card or USB stick plugged in, one of the first things to pop up on the screen (so quickly that usually I don't even notice) looks a ...
14
votes
2answers
17k 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 ...
4
votes
1answer
5k views

How can I uniquely identify which device is on USB `hub 6-0:1.0: port 2`?

How can I uniquely identify which device is on USB hub 6-0:1.0: port 2? I receive messages in my dmesg every now and then and I want the system to tell me which device is connected to that port. ...
3
votes
2answers
2k views

Perform an action when a wireless keyboard is connected

I need to perform a command when I connect a bluetooth keyboard. How can I 'listen' this event?
2
votes
2answers
191 views

What do device type numbers mean?

file /dev/* prints the description of a bunch of files as "block special (M/N)" and "character special (M/N)", where M and N are numbers. For example: $ file /dev/null /dev/null: character special (1/...
79
votes
4answers
313k views

How can I find available network interfaces?

This is in regard to linux, but if anyone knows of a general *nix method that would be good. I booted a system yesterday with an ethernet cable plugged in. "NetworkManager" is not installed, so once ...
31
votes
1answer
10k views

What do the device files in /dev actually do?

(Not a duplicate of Understanding /dev and its subdirs and files) I was browsing around my filesystem and for the first time I took a second to analyze my /dev directory. I was surprised by the ...
86
votes
3answers
10k views

What does the letter 'u' mean in /dev/urandom?

I understand that reads to /dev/random may block, while reading /dev/urandom is guaranteed not to block. Where does the letter u come into this? What does it signify? Userspace? Unblocking? Micro? ...
17
votes
3answers
57k 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, ...
19
votes
2answers
10k views

Manipulating /dev/video

I'd like to take the video stream from /dev/video0, apply some effects or changes and make the result available on /dev/video1. /dev/video0 ---> Apply Effects ---> /dev/video1 For example, mplayer ...
29
votes
1answer
22k views

Difference between /dev and /sys/class?

What is the difference between the device representation in /dev and the one in /sys/class? Is one preferred over the other? Is there something one offers and the other doesn't?
24
votes
1answer
34k 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 ...