Exploring the Physical Web

Physical Web

Introduction

Objects around you that are part of the Physical Web send Bluetooth signals to your phone. When you’re in range, you’ll see a list of suggested webpages.

Client side

You can run the client app on your smart phone that will through bluetooth to scan any objects nearby you. And list out the URLs. (hints: I found a Brother’s printer on the app)
iOS app store
Android

Server side

You can build you only Physical Web in few steps really quick.
https://apkpure.com/beacon-toy/com.uriio

Reference

https://google.github.io/physical-web/
https://github.com/google/physical-web

Setup SMART on ubuntu server

Ubuntu

Installation

1
apt-get install smartmontools

Configuation

1
2
3
4
5
6
7
8
9
10
11
12
13
cat /etc/default/smartmontools
# file content
enable_smart="/dev/sda /dev/sdb"
start_smartd=yes
smartd_opts="--interval=1800"


cat  /etc/smartd.conf
# file content
DEVICESCAN -d removable -n standby -m root -M exec /usr/share/smartmontools/smartd-runner
/dev/sda -a -o on -S on -s (S/../.././02|L/../../6/03)
/dev/sda -H -l error -l selftest -t -I 194
/dev/sda -H -C 0 -U 0 -m calvin@test.com.tld

Start Service

1
2
/etc/init.d/smartd start
systemctl enable smartd

Log

1
cat /var/log/syslog

Docker compose error (mem_limit)

Docker

Senario

When you try to run container with ./docker-compose.yml file, you will get below error message.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Traceback (most recent call last):
  File "docker-compose", line 6, in <module>
  File "compose/cli/main.py", line 71, in main
  File "compose/cli/main.py", line 121, in perform_command
  File "compose/cli/command.py", line 37, in project_from_options
  File "compose/cli/command.py", line 91, in get_project
  File "compose/config/config.py", line 375, in load
  File "compose/config/config.py", line 506, in process_config_file
  File "compose/config/config.py", line 497, in interpolate_config_section
  File "compose/config/interpolation.py", line 44, in interpolate_environment_variables
  File "compose/config/interpolation.py", line 44, in <genexpr>
  File "compose/config/interpolation.py", line 39, in process_item
  File "compose/config/interpolation.py", line 39, in <genexpr>
  File "compose/config/interpolation.py", line 54, in interpolate_value
  File "compose/config/interpolation.py", line 74, in recursive_interpolate
  File "compose/config/interpolation.py", line 74, in <genexpr>
  File "compose/config/interpolation.py", line 70, in recursive_interpolate
  File "compose/config/interpolation.py", line 184, in convert
  File "compose/config/interpolation.py", line 141, in to_int
ValueError: invalid literal for int() with base 0: '512m'
Failed to execute script docker-compose

Summary

The value of mem_limit no more supported with recent docker-compose (1.18.0)

Hot-fix

Just edit your docker-compose.yml and remove mem_limit lines. The best soloution should be replace as RESOURCES.

1
2
3
4
5
6
7
8
# backup your file
cp -a docker-compose.yml docker-compose.yml.bak

# trim mem_limit
cat docker-compose.yml.bak |grep -v "mem_limit" > docker-compose.yml

# then run again
docker-compose up

Reference

https://support.zabbix.com/browse/ZBX-13224
https://docs.docker.com/compose/compose-file/#resources

Docker ubuntu container network utilities

Docker

Senario

When you need to debug the container you may need some network tools.

1
docker exec -it your_container_name bash

Packages

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
apt-get update
apt-get install -y iputils-ping telnet dnsutils net-tools inetutils-traceroute

# You must run update before your installation
apt-get update

# ping google.com
apt-get install iputils-ping

# telnet google.com 80
apt-get install telnet

# nslookup google.com
# host google.com
apt-get install dnsutils

# netstat, arp
apt-get install net-tools

# traceroute google.com
apt-get install inetutils-traceroute

Bad Sector and MySQL innodb

MySQL

StdErr

Thats shown on screen

1
2
3
4
WARNING: Your hard drive is failing
Device: /dev/sda [SAT], 8 Currently unreadable (pending) sectors
WARNING: Your hard drive is failing
Device: /dev/sda [SAT], 8 Offline uncorrectable sectors

SMART Log

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
# sudo smartctl -a /dev/sda
...
...
SMART Error Log Version: 1
ATA Error Count: 25 (device log contains only the most recent five errors)
...
...
Error 25 occurred at disk power-on lifetime: 6502 hours (270 days + 22 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  40 51 00 ff ff ff 0f  Error: UNC at LBA = 0x0fffffff = 268435455

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC   Powered_Up_Time  Command/Feature_Name
  -- -- -- -- -- -- -- --  ----------------  --------------------
  25 00 08 ff ff ff ef 00  14d+16:54:04.035  READ DMA EXT
  27 00 00 00 00 00 e0 00  14d+16:54:04.031  READ NATIVE MAX ADDRESS EXT [OBS-ACS-3]
  ec 00 00 00 00 00 a0 00  14d+16:54:03.993  IDENTIFY DEVICE
  ef 03 45 00 00 00 a0 00  14d+16:54:03.990  SET FEATURES [Set transfer mode]
  27 00 00 00 00 00 e0 00  14d+16:54:03.990  READ NATIVE MAX ADDRESS EXT [OBS-ACS-3]
...
...
SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed: read failure       10%      6410         1468496680
...
...

MySQL Log

1
2
3
4
5
6
7
8
9
10
2018-01-08  9:38:25 140666168350528 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2018-01-08  9:38:25 140666168350528 [Note] InnoDB: Completed initialization of buffer pool
2018-01-08  9:38:32 140666168350528 [ERROR] InnoDB: Tried to read 1048576 bytes at offset 2097152. Was only able to read 163840.
2018-01-08 09:38:32 7fef64ff1740  InnoDB: Operating system error number 5 in a file operation.
InnoDB: Error number 5 means 'Input/output error'.
InnoDB: Some operating system error numbers are described at
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/operating-system-error-codes.html
 InnoDB: Operation read to file /tmp/mariadb-10.1.14/storage/xtradb/os/os0file.cc and at line 3160
2018-01-08  9:38:32 140666168350528 [ERROR] InnoDB: File (unknown): 'read' returned OS error 205. Cannot continue operation
180108 09:38:32 mysqld_safe mysqld from pid file /usr/local/data/mysql/data/mysqld.pid ended

Conclusion

‘Input/output error’ most likely means harddisk error!
Please backup ASAP!

Go Programming Language

GoLang

Installation

1
2
3
4
5
6
# download: https://golang.org/doc/install

# set Path
export PATH=$PATH:/usr/local/go/bin
export GOROOT=$HOME/go1.X
export PATH=$PATH:$GOROOT/bin

Source code

1
2
3
4
5
6
7
package main

import "fmt"

func main() {
    fmt.Printf("hello, world\n")
}

Compile

1
2
cd $HOME/go/src/hello
go build

Execute

1
2
./hello
# output: hello, world

Serverless JAMstack

JAMstack

JAMstack

Javascript, APIs, Markup

Markup Generator

  • JekyII - jekyllrb.com
  • Hugo - gohugo.io
  • Hexo - hexo.io
  • Octopress - octopress.org
  • Gatsby - github.com/gatsbyjs
  • Pelican - getpelican.com
  • Brunch - brunch.io
  • Metalsmith - metalsmith.io
  • Middleman - middlemanapp.com
  • Nuxt - nuxtjs.org
  • StaticGen - staticgen.com

JavaScript

Do something to connect your APIs.

APIs

  • Contentful
  • Netlify
  • Algolia

Reference

https://jamstack.org/