Summer Nights

• docker pull image_name
• docker create ….. (create container from image)
• docker run …. (create container and run from image)
• docker ps -a (list all container, including stopped)
• docker images (list all images)
• docker rm container_name (delete container)
• docker start container_name (start/resume container)
• docker stop container_name  (stop container)
• docker rmi image_name (delete image)
• docker exec -it container_name bash (connect to running conatiner_name container and jump to a bash shell)

After upgrading to a newer Ubuntu, I found myself facing automatic system suspend events (look at /var/log/syslog) every 20 or 30 minutes. Here is how to fix them:

sudo -H -u lightdm dbus-launch --exit-with-session dbus-launch gsettings set com.canonical.unity-greeter idle-timeout 0

sudo -H -u lightdm dbus-launch --exit-with-session dbus-launch gsettings set org.gnome.settings-daemon.plugins.power lid-close-ac-action nothing

sudo -H -u lightdm dbus-launch --exit-with-session dbus-launch gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 0

sudo -H -u lightdm dbus-launch --exit-with-session dbus-launch gsettings set org.gnome.settings-daemon.plugins.power time-low 0

You might want to look at the power settings first which can be shown by:

sudo -H -u lightdm dbus-launch --exit-with-session gsettings list-recursively org.gnome.settings-daemon.plugins.power

If needed, login to the lightdm user by:

su lightdm -s /bin/bash

Not frequently but once in a while you would need to replace your “troubling” hard disk with a new shiny one. In order to keep all your mapping intact, you would like to use the same UUIDs and even the partition map. But as the new hard disk is generally a larger size, it makes sense to expand the main partition to the end of the drive. So here are some commands to do this job.

First make a copy of the existing partition table:

sfdisk -d /dev/sda > sda.dump

Now shutdown the computer, remove the old disk, and install the new disk. After booting, copy the partition table to the new disk.

sfdisk /dev/sda < sda.dump

Now open parted and expand the last partition through the end of the available space

parted /dev/sda
..print (to see the table)
..resizepart (use the end figure from the table to expand to the end)

Format the newly created partitions.

mkfs.ext4 /dev/sda1
mkfs.ext4 /dev/sda2

Everything should be alright now but if needed, you can also manually apply the UUIDs.

tune2fs /dev/sda1 -U xxxxe50b-89d4-xxxx-8d8e-e6c4d547xxxx
tune2fs /dev/sda2 -U xxxxae63-xxxx-4054-b55d-b52f751xxxxx

Often we would like to monitor the online status of one or more websites or urls in order to be able to fix any issues as soon as a problem arises. I created the following simple mechanism to probe a list of url’s and send push notifications in case of an error.

#!/usr/bin/env python3

# Script to check url health and send push notifications using pushover servrice
# Author: Dr. Asif Rana (aiqbalrana@gmail.com)
# License: MIT License 
# Date: 20180213, 12:06 CET

import urllib.request
import http.client, urllib
import sys
sitelist = {
  'http://site1url/' : 'site1 label',
  'http://site2url/' : 'site2 label', }
for x in sitelist:
  statuslive = 0
  try:
    url = urllib.request.urlopen(x)
    code = url.getcode()
    if (code == 200):
      statuslive = 1
  except:
    statuslive = 0
 
  if (statuslive == 0):
    conn = http.client.HTTPSConnection("api.pushover.net:443")
    conn.request("POST", "/1/messages.json", urllib.parse.urlencode({
    "token": "your pushover.net application token",
    "user": "your pushover.net user key", "
    message": "Site down: " + sitelist[x], }), { "Content-type": "application/x-www-form-urlencoded" })
    conn.getresponse()

Ideally, you would run this script on a different server than the site you would like to monitor. A pushover.net account will be needed to get your token and key. In addition, you would need to install the pushover app on your iOS or Android device to get the notifications.

Tested and works great for a simple URL monitoring and getting notifications about website crashes, etc.!

You need to add this script as a cronjob using crontab tool and run it on regular intervals (e.g., every 5 minutes) to check the urls.

In ossec.conf:

<active-response>
    <repeated_offenders>60,120,1440</repeated_offenders>
 </active-response>

where 60, 120, 1440 indicate minutes banned after first, second, and third offense. Adapt these values to your taste.

apt install software-properties-common
add-apt-repository ppa:certbot/certbot
apt update
apt-get install python-certbot-apache
certbot-auto -d www.domain.com -d subdomain.domain.com -d subdomain2.domain.com  -d domain.com

This should install the certificates for all the domains in their respective sections (443) in the apache config file.

Now the certificates should be renewed every 90 days: Test renewal by doing a dry run:
certbot renew --dry-run

If everything works, then configure a fully automatic renewal via a cron job, e.g.,
0 0 15 * * /usr/bin/certbot renew --quiet

• Edit /etc/bind/db.domainname.com
• Increase the serial number and add the following line:
  subdomain IN A xx.xx.xx.xx
• named-checkconf
• service bind9 restart