Linux Skills

How to deal with Access Denied problem when granting/revoking privileges

Shutdown MySQL server.
Run MySQL server with command mysqld_safe --skip-grant-table.
Execute SQL statements for granting/revoking privileges.
Kill the mysqld_safe process started at step 2.
Restart MySQL server.

Run program at startup via crontab

Add the following content to /etc/crontab:

@reboot    username    /path/to/script arguments

Keep Laptop Running When Closing Lid

Edit /etc/systemd/login.conf and change the value of HandleLidSwitch to ignore.

Improve Sound Quality for ALSA

Open /usr/share/alsa/alsa.conf, then change defaults.pcm.dmix.rate 48000 into defaults.pcm.dmix.rate 44100.

Configure autologin for Linux console using `systemd`

Firstly, Create directory /etc/systemd/system/getty@tty1.service.d/ if not exist.

Then create file /etc/systemd/system/getty@tty1.service.d/autologin.conf with the following content:

[Service]
ExecStart=
ExecStart=-/sbin/agetty --autologin username --noclear %I $TERM

Then save and reboot.

Change Date/Time/Timezone Under Linux

Change date: date -s MM/DD/YYYY

Change time: date -s hh:mm:ss

Change timezone: sudo dpkg-reconfigure tzdata

Record System Output Sound In Linux

When pulseaudio is used as the sound server of the system, there is a simple way to record the output sound to file on the command line using pacat command.

Step 1: Find out the correct device

In order to find the correct device, you should run this command:

pacmd list | grep "\.monitor"

When you see something like this:

	name: <alsa_output.pci-0000_00_1b.0.analog-stereo.monitor>
	alsa_output.pci-0000_00_1b.0.analog-stereo.monitor/#0: Monitor of Built-in Audio Analog Stereo

and the soundcard corresponds to the one you want to monitor, you can find out which device name to use. Here it is:

alsa_output.pci-0000_00_1b.0.analog-stereo.monitor

Step 2: Start recording system output sound

Here are examples of how to record system output sound to a .wav file with CD audio quality.

Command using sox:

pacat --record -d alsa_output.pci-0000_00_1b.0.analog-stereo.monitor | sox -t raw -r 44100 -s -L -b 16 -c 2 - output.wav

Command using ffmpeg:

pacat --record -d alsa_output.pci-0000_00_1b.0.analog-stereo.monitor | ffmpeg -f s16le -ar 44.1k -ac 2 -i pipe:0 record.wav

Wifi Configuration Under Linux Console

Preparation

Use ifconfig -a to show all the network interfaces available.

Solution 1 (Connect to one AP only)

Add the following configuration to /etc/network/interfaces:

auto wlan0
iface wlan0 inet dhcp
	wpa-ssid "WLAN_SSID"
	wpa-psk "12345678"

wlan0 should be replaced with the Wifi device in use.

Solution 2 (Connect to different APs based on signal strength)

Step 1: Create /etc/network/wpa_supplicant.conf with following configuration:

network={
	ssid="WLAN_AP_1"
	key_mgmt=WPA-PSK
	psk="WLAN_AP_PSK_1"
	priority=1
}
network={
	ssid="WLAN_AP_2"
	key_mgmt=WPA-PSK
	psk="WLAN_AP_PSK_2"
	priority=2
}

Step 2: Add the following configuration to /etc/network/interfaces

auto wlan0
iface wlan0 inet dhcp
	wpa-conf /etc/network/wpa_supplicant.conf