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My blog moved from http://alexanderlobov.ru to http://alexanderlobov.net

New blog

My new blog is here: alexanderlobov.ru

Inserting code with syntax highlighting into HTML

I use this service: https://tohtml.com/

How to reset usb device from console (for example, usb wi-fi device)

I use external USB wi-fi for my desktop with Ubuntu. Occasionally after waking up this device does not work. I do not know the cause root of the issue, but there are several solution to relieve: pull out and then put in the device into usb port, or do the same thing programmatically as described below. Create a file usbreset.c (I placed it to ~/src/usbreset):

/* usbreset -- send a USB port reset to a USB device
 * Source:
 * http://askubuntu.com/questions/645/how-do-you-reset-a-usb-device-from-the-command-line
 */


/* How to find device name:
 *  lsusb
 * Find your device in the output, see the "Bus" and "Device numbers"
 * Device name is
 *  /dev/bus/usb/<bus>/<device number>
 * For example,
 *  /dev/bus/usb/001/001
 */

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>

#include <linux/usbdevice_fs.h>

int main(int argc, char **argv)
{
    const char *filename;
    int fd;
    int rc;

    if (argc != 2) {
        fprintf(stderr, "Usage: usbreset device-filename\n");
        return 1;
    }
    filename = argv[1];

    fd = open(filename, O_WRONLY);
    if (fd < 0) {
        perror("Error opening output file");
        return 1;
    }

    printf("Resetting USB device %s\n", filename);
    rc = ioctl(fd, USBDEVFS_RESET, 0);
    if (rc < 0) {
        perror("Error in ioctl");
        return 1;
    }
    printf("Reset successful\n");

    close(fd);
    return 0;
}

Source of this code

Compile the code:

cc usbreset.c -o usbreset

Make the file executable

chmod +x usbreset

Then, you can repeat the steps from this answer every time you need to restart the device. But you need to run manually lsusb, generate path to the device, and input superuser password every time. You can automatize this. We need to change owner to root and set setuid bit on the executable:

sudo chown root:root ~/src/usbreset/usbreset
sudo chmod 4755 usbreset

We can see

$ ls -l usbreset
-rwsr-xr-x 1 root root 8906 Sep 16  2015 usbreset

My PATH contains ~/bin directory, so in ~/bin I create symlink to the executable

ln -s ~/src/usbreset/usbreset usbreset-bin

$ ll usbreset-bin 
lrwxrwxrwx 1 alex alex 32 Oct  9 12:46 usbreset-bin -> /home/alex/src/usbreset/usbreset*

Create a file usbreset in ~/bin

#!/usr/bin/python

import subprocess

devices = subprocess.check_output(['lsusb']).splitlines()
wifi_devices = filter(lambda x: '802.11n' in x, devices)
assert len(wifi_devices) == 1
wifi_device = wifi_devices[0]
items = wifi_device.split(":")[0].split(" ")
assert len(items) == 4
assert items[0] == "Bus"
bus = items[1]
assert items[2] == "Device"
device = items[3]

device_path = "/dev/bus/usb/{bus}/{device}".format(bus = bus, device = device)
subprocess.call(("/home/alex/bin/usbreset-bin", device_path))

You need to change "/home/alex" path to your home directory. Then, you can just run

usbreset

in console for usb wi-fi resetting.

Cheatsheet: Linux video conversion with avconv

Case: you have a "vertical video" from a phone and want to transpose it. To transpose a video:

avconv -i input-video.mp4 -vf "transpose=1" output-video.mp4

Youtube fullscreen with xmonad

Source

import XMonad.Hooks.EwmhDesktops

main = do
    xmonad $ ewmh defaultConfig
        ...
        , handleEventHook = fullscreenEventHook <+> handleEventHook defaultConfig

Toggle layout with X Window System

setxkbmap -option "ctrl:nocaps"
setxkbmap -layout "us,ru" -option "grp:lalt_lshift_toggle"

Where to place the code