atitan

#!/bin/bash

# Copyright © 2017 Google Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software

atitan

# Drop other people's session
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE datname = current_database() AND pid <> pg_backend_pid();

# Change passwd
ALTER USER user_name WITH PASSWORD 'new_password';

ALTER ROLE migrator CREATEDB;

atitan

Problem

Installing mysql2 gem errors on MacOS Mojave.

Solution

Make sure openssl is installed on Mac via Homebrew.

brew install openssl

atitan

#!/bin/bash

yum install -y jq curl

while sleep 5; do
  if [ -z $(curl -Isf http://169.254.169.254/latest/meta-data/spot/instance-action) ]; then
    /bin/false
  else
    EC2_INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
    EC2_AVAIL_ZONE=`curl -s http://169.254.169.254/latest/meta-data/placement/availability-zone`

atitan

require 'cgi'
require 'json'
require 'active_support'

def verify_and_decrypt_session_cookie(cookie, secret_key_base)
  cookie = CGI::unescape(cookie)
  salt         = 'encrypted cookie'
  signed_salt  = 'signed encrypted cookie'
  key_generator = ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
  secret = key_generator.generate_key(salt)[0, ActiveSupport::MessageEncryptor.key_len]

atitan

Setup redis-cli on AWS EC2

SSH into your EC2 instance. Run the following:

$ sudo yum install gcc This may return an "already installed" message. That's OK.

$ wget http://download.redis.io/redis-stable.tar.gz && tar xvzf redis-stable.tar.gz && cd redis-stable && make

See: http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/GettingStarted.ConnectToCacheNode.Redis.html

atitan

JQ to filter JSON by value

Syntax: cat <filename> | jq -c '.[] | select( .<key> | contains("<value>"))'

Example: To get json record having _id equal 611

cat my.json | jq -c '.[] | select( ._id | contains(611))'

Remember: if JSON value has no double quotes (eg. for numeric) to do not supply in filter i.e. in contains(611)

atitan

Processing JSON using jq

jq is useful to slice, filter, map and transform structured json data.

Installing jq

On Mac OS

brew install jq

atitan

#!/bin/bash

# get the latest linux kernel at http://kernel.ubuntu.com/~kernel-ppa/mainline/
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.14-rc6/linux-image-4.14.0-041400rc6-generic_4.14.0-041400rc6.201710230731_amd64.deb

# install the kernel
dpkg -i linux-image-4.*.deb

# update grub
# for linode, change kernel in boot settings to GRUB 2

atitan

#!/bin/sh
## backup each mysql db into a different file, rather than one big file
## as with --all-databases. This will make restores easier.
## To backup a single database simply add the db name as a parameter (or multiple dbs)
 
## Putting the script in /var/backups/mysql seems sensible... on a debian machine that is
## Create the user and directories
# mkdir -p /var/backups/mysql/databases
# useradd --home-dir /var/backups/mysql --gid backup --no-create-home mysql-backup
## Remember to make the script executable, and unreadable by others