How to Fix Error: Failed to Download Metadata for Repo ‘AppStream’

To fix the above error, open your terminal or login via ssh or terminal, and run the following commands to change the repo URL to point to vault.centos.org, from the official CentOS repos.

Here we use the sed command to edit the required directives or parameters in the repo configuration files:

# sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*

# sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*

Alternatively, you can also point to the Cloudflare-based vault repository, by running the following commands:

# sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-Linux-*

# sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.epel.cloud|g' /etc/yum.repos.d/CentOS-Linux-*

Now you should be able to update CentOS or install packages without any error:

Error on your browser: the website sent back unusual and incorrect credentials

Normally uses encryption to protect your information when Chrome tried to connect to

.... the website sent back unusual and incorrect credentials .....

as they say, your browser has HSTS problem. 

Usually you need to make sure your Webmin configuration. Yaa, I mean this case maybe occurs on your access to port 10000. 

I thing your SSL was worked to all domain but not to Webmin, so to resolve it, you can go to /etc/webmin/miniserv.conf

add new line to that file:

inetd_ssl=1

save and restart Webmin. So you can check it with your domain such as: https://mydomain.com:10000

Problem:

Message: Array and string offset access syntax with curly braces is deprecated

Resolve:

search variable with {0} change it to [0]

-------

Problem:

Trying to access array offset on value of type int cell/DefaultValueBinder.php

} elseif ($pValue[0] === '=' && strlen($pValue) > 1) {

Resolve:

} elseif (0 === strpos($pValue, '=') && strlen($pValue) > 1) {

-------

Problem:

Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead) in htdocs

A PHP Error was encountered

Severity: Compile Error

Message: Cannot use isset() on the result of an expression (you can use "null !== expression" instead)

Resolve:

change isset($param) to (null !== $param)

-------

Setup I2C LCD on Raspberry pi

I2C (inter-integrated circuit) uses two wires to send and receive data and two wires to Vcc and ground.

- install I2C-tools: sudo apt-get install i2c-tools.

- install SMBUS: sudo apt-get install python-smbus.

- reboot.

- connect the I2C LCD to Raspi

- in terminal: i2cdetect -y 1 . This will show a table of addresses for each I2C device connected to Pi.

- put the I2C address of your LCD in line 22 of the library code. For example, my I2C address is 21, so I’ll change line 22 to ADDRESS = 0x3f.

- in terminal: nano I2C_LCD_driver.py

# -*- coding: utf-8 -*-
# Original code found at:
# https://gist.github.com/DenisFromHR/cc863375a6e19dce359d
"""
Compiled, mashed and generally mutilated 2014-2015 by Denis Pleic
Made available under GNU GENERAL PUBLIC LICENSE
# Modified Python I2C library for Raspberry Pi
# as found on http://www.recantha.co.uk/blog/?p=4849
# Joined existing 'i2c_lib.py' and 'lcddriver.py' into a single library
# added bits and pieces from various sources
# By DenisFromHR (Denis Pleic)
# 2015-02-10, ver 0.1
"""
# i2c bus (0 -- original Pi, 1 -- Rev 2 Pi)
I2CBUS = 1
# LCD Address
ADDRESS = 0x3f
import smbus
from time import sleep
class i2c_device:
   def __init__(self, addr, port=I2CBUS):
      self.addr = addr
      self.bus = smbus.SMBus(port)
# Write a single command
   def write_cmd(self, cmd):
      self.bus.write_byte(self.addr, cmd)
      sleep(0.0001)
# Write a command and argument
   def write_cmd_arg(self, cmd, data):
      self.bus.write_byte_data(self.addr, cmd, data)
      sleep(0.0001)
# Write a block of data
   def write_block_data(self, cmd, data):
      self.bus.write_block_data(self.addr, cmd, data)
      sleep(0.0001)
# Read a single byte
   def read(self):
      return self.bus.read_byte(self.addr)
# Read
   def read_data(self, cmd):
      return self.bus.read_byte_data(self.addr, cmd)
# Read a block of data
   def read_block_data(self, cmd):
      return self.bus.read_block_data(self.addr, cmd)

# commands
LCD_CLEARDISPLAY = 0x01
LCD_RETURNHOME = 0x02
LCD_ENTRYMODESET = 0x04
LCD_DISPLAYCONTROL = 0x08
LCD_CURSORSHIFT = 0x10
LCD_FUNCTIONSET = 0x20
LCD_SETCGRAMADDR = 0x40
LCD_SETDDRAMADDR = 0x80
# flags for display entry mode
LCD_ENTRYRIGHT = 0x00
LCD_ENTRYLEFT = 0x02
LCD_ENTRYSHIFTINCREMENT = 0x01
LCD_ENTRYSHIFTDECREMENT = 0x00
# flags for display on/off control
LCD_DISPLAYON = 0x04
LCD_DISPLAYOFF = 0x00
LCD_CURSORON = 0x02
LCD_CURSOROFF = 0x00
LCD_BLINKON = 0x01
LCD_BLINKOFF = 0x00
# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00
LCD_MOVERIGHT = 0x04
LCD_MOVELEFT = 0x00
# flags for function set
LCD_8BITMODE = 0x10
LCD_4BITMODE = 0x00
LCD_2LINE = 0x08
LCD_1LINE = 0x00
LCD_5x10DOTS = 0x04
LCD_5x8DOTS = 0x00
# flags for backlight control
LCD_BACKLIGHT = 0x08
LCD_NOBACKLIGHT = 0x00
En = 0b00000100 # Enable bit
Rw = 0b00000010 # Read/Write bit
Rs = 0b00000001 # Register select bit
class lcd:
   #initializes objects and lcd
   def __init__(self):
      self.lcd_device = i2c_device(ADDRESS)
      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x02)
      self.lcd_write(LCD_FUNCTIONSET | LCD_2LINE | LCD_5x8DOTS | LCD_4BITMODE)
      self.lcd_write(LCD_DISPLAYCONTROL | LCD_DISPLAYON)
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_ENTRYMODESET | LCD_ENTRYLEFT)
      sleep(0.2)

   # clocks EN to latch command
   def lcd_strobe(self, data):
      self.lcd_device.write_cmd(data | En | LCD_BACKLIGHT)
      sleep(.0005)
      self.lcd_device.write_cmd(((data & ~En) | LCD_BACKLIGHT))
      sleep(.0001)
   def lcd_write_four_bits(self, data):
      self.lcd_device.write_cmd(data | LCD_BACKLIGHT)
      self.lcd_strobe(data)
   # write a command to lcd
   def lcd_write(self, cmd, mode=0):
      self.lcd_write_four_bits(mode | (cmd & 0xF0))
      self.lcd_write_four_bits(mode | ((cmd << 4) & 0xF0))
   # write a character to lcd (or character rom) 0x09: backlight | RS=DR<
   # works!
   def lcd_write_char(self, charvalue, mode=1):
      self.lcd_write_four_bits(mode | (charvalue & 0xF0))
      self.lcd_write_four_bits(mode | ((charvalue << 4) & 0xF0))
  
   # put string function with optional char positioning
   def lcd_display_string(self, string, line=1, pos=0):
    if line == 1:
      pos_new = pos
    elif line == 2:
      pos_new = 0x40 + pos
    elif line == 3:
      pos_new = 0x14 + pos
    elif line == 4:
      pos_new = 0x54 + pos
    self.lcd_write(0x80 + pos_new)
    for char in string:
      self.lcd_write(ord(char), Rs)
   # clear lcd and set to home
   def lcd_clear(self):
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_RETURNHOME)
   # define backlight on/off (lcd.backlight(1); off= lcd.backlight(0)
   def backlight(self, state): # for state, 1 = on, 0 = off
      if state == 1:
         self.lcd_device.write_cmd(LCD_BACKLIGHT)
      elif state == 0:
         self.lcd_device.write_cmd(LCD_NOBACKLIGHT)
   # add custom characters (0 - 7)
   def lcd_load_custom_chars(self, fontdata):
      self.lcd_write(0x40);
      for char in fontdata:
         for line in char:
            self.lcd_write_char(line)

- Now, we can test it with hello world, in terminal: nano test.py

import I2C_LCD_driver
mylcd = I2C_LCD_driver.lcd()
mylcd.lcd_display_string("Hello world", 1)

- make sure, you have python installed and between library and python files in one directory.

- run it in terminal: python test.py