Using sed to format a phone number

Formatting an unformated “phone” number using sed.

There may be a different and easier way to do this, but the main thing to learn here is the ^, $, and [[:digit:]] options.

^ refers to the first part of a line
& which is our searched for pattern
$ refers to an end part of the line
[[:digit:]] searches for, you guessed it. Digits!

The following command reads the incoming 10 digit number form echo and does the following.

the ^ tells it that the pattern needs to match at the beginning of the line
[[:digit:]] repeated tells it to search for three consecutive digits
(&) tells it to put brackets around the & which is our searched for pattern in the first part.
We then pipe that to another sed command which
searches for 4 consecutive digits
the $ tells it that it needs to be at the end of the line.

echo "1234567890" | sed -e 's/^[[:digit:]][[:digit:]][[:digit:]]/(&) /g' | sed -e 's/[[:digit:]][[:digit:]][[:digit:]][[:digit:]]$/-&/g'

Resulting output is

(123) 456-7890

The following link was helpful while searching what the ^ and $ options do.

https://www.computerhope.com/unix/used.htm

Ping multiple IP addresses to see if they are up or down

An easy way to do this is by using fping. fping is a little bit easier ping utility to use then normal ping when trying to verify that a host is actually down.

By default fping returns if a host is “alive” or “unreachable”

Example:

$ fping 192.168.1.4
192.168.1.4 is alive

Or for a host that is down it returns something like the following

$ fping 192.168.1.5
ICMP Host Unreachable from 192.168.1.2 for ICMP Echo sent to 192.168.1.5
ICMP Host Unreachable from 192.168.1.2 for ICMP Echo sent to 192.168.1.5
ICMP Host Unreachable from 192.168.1.2 for ICMP Echo sent to 192.168.1.5
ICMP Host Unreachable from 192.168.1.2 for ICMP Echo sent to 192.168.1.5
192.168.1.5 is unreachable

You can adjust the retry rate with the -r option, default is 3 which it has multiple of the Host Unreachable lines. Changing it to 1 or 2 gets rid of those lines so it just shows that the host is unreachable.

$ fping -r 1 192.168.1.5
192.168.1.5 is unreachable

Ping multiple addresses

Fortunately pinging multiple addresses with fping is as easy as adding them to the end of the command. For example

fping -r1 192.168.1.1 192.168.1.2

will ping both the specified addresses one after the other and print the results to the terminal.

Example:

$ fping -r 192.168.1.1 192.168.1.10 192.168.1.45  
192.168.1.1 is alive
192.168.1.10 is alive
192.168.1.45 is unreachable

Snapper reverting changes on Fedora

List snapper BTRFS snapshots with

snapper list

If you are in recovery mode on Fedora, add –no-dbus right after the snapper command. e.g.

snapper --no-dbus list

You can use the diff command to list the changes that happened between snapshots.

snapper --no-dbus diff 108..109

And to undo a change or all the changes between a snapshot, do the following. Where 108..109 are all the changes you want to remove. So essentially going back to snapshot 108.

snapper --no-dbus -v undochange 108..109

https://documentation.suse.com/sles/11-SP4/html/SLES-all/cha-snapper.html

Installing a specific package version on Ubuntu

On Ubuntu and potentially other Debian based distributions, you can check the available versions of a package with the apt show command

apt show -a

Example showing firefox versions

~$ apt show -a firefox
Package: firefox
Version: 87.0+build3-0ubuntu0.20.04.2
Priority: optional
Section: web
Origin: Ubuntu
Maintainer: Ubuntu Mozilla Team <ubuntu-mozillateam@lists.ubuntu.com>
..................
 More information
..................

Package: firefox
Version: 75.0+build3-0ubuntu1
Priority: optional
Section: web
Origin: Ubuntu
Maintainer: Ubuntu Mozilla Team <ubuntu-mozillateam@lists.ubuntu.com>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
..................

To install a specific version, use the version number

sudo apt install firefox=75.0+build3-0ubuntu1

Error: Could not create the Java Virtual Machine

Apparently on some versions of Java checking the Java version will give you the following error.

root@local:~# java -v
Unrecognized option: -v
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
root@local:~#

The issue being the -v or –version options are not recognized. On newer versions of Java it is recognized.

The proper way to do it is -version with only one dash

root@local:~# java -version
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-8u252-b09-1ubuntu1-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)
root@local:~#

https://askubuntu.com/questions/324858/installed-jdk-by-and-have-error-could-not-create-the-java-virtual-machine

Backup Matrix Synapse PostgreSQL Database

This is part of a series of posts on backing up and restoring a backup for Matrix Synapse server. Synapse was installed using the matrix-docker-ansible deployment which while a little complicated can greatly ease management later on down the road. All the main components are in docker containers so we need to use docker to access.

https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/docs/maintenance-postgres.md#backing-up-postgresql

As the root user run

docker exec --env-file=/matrix/postgres/env-postgres-psql matrix-postgres pg_dumpall -h matrix-postgres | gzip -c > /matrix/postgres.sql.gz

This will dump the Postgres database in /matrix/postgres.sql.gz
We can use this later to restore to a new server or keep as a backup.

Configure rsnapshot on Ubuntu Server

rsnapshot is a utility that uses rsync to backup files locally or it can backup files from a remote server.

While trying to figure out a good solution for backing up an Ubuntu Server I decided to try rsnapshot, however since it can either create a local backup or pull a remote backup it needs to be configured to do that on the backup server side. It does not “push” a backup to a backup server.

Some helpful snippits from the man file.

rsnapshot will typically be invoked as root by a cron job, or series of cron jobs. It is possible, however, to run as any    arbitrary user with an alternate configuration file.
...
USAGE
        rsnapshot can be used by any user, but for system-wide backups you will probably want to run it as root.
...
NOTES
        Make sure your /etc/rsnapshot.conf file has all elements separated by tabs.  See
        /usr/share/doc/rsnapshot/examples/rsnapshot.conf.default.gz for a working example file.
    Make sure you put a trailing slash on the end of all directory references.  If you don't, you may have extra directories    created in your snapshots.  For more information on how the trailing slash is handled, see the rsync(1) manpage.

Overview

Scenario

Host A runs xyz application and host B is the backup server. We create a backup user on host A, host B then uses that user to ssh and rsync backups to itself.

  1. Create backup user
  2. Configure rysnc to be used without a password
  3. Setup SSH Key, aka Passwordless authentication (On backup server)
  4. Setup rsnapshot config (On backup server)
  5. Configure rsnapshot in crontab (On backup server)
  6. Final Testing

Create backup user

The following commands are fairly straight forward. Change backupuser to whatever you want to call your backup user.

sudo useradd -m backupuser
passwd backupuser
sudo usermod -a -G sudo backupuser

Configure rysnc to be used without a password

We need to setup the backup user to be able to use “sudo rsync” without having to input the user password. If we don’t use sudo we can’t access system files for backups. And if we have to manually input the password every time rsync runs, then the backups would not be automatic. The following link was helpful.

https://unix.stackexchange.com/questions/325100/proper-way-to-set-up-rsnapshot-over-ssh

All we need to do is create a file in /etc/sudoers.d/username and then tell it we don’t need to enter a password when “sudo rsync” is run.

sudo tee /etc/sudoers.d/backupuser <<<'backupuser ALL = (root) NOPASSWD: /usr/bin/rsync'

Setup SSH Key, aka Passwordless authentication (On backup server)

Log into the backup server

Create SSH keys. Note that since rsnapshot wants to run as root, we create the key and copy it as the root user.

sudo ssh-keygen

Accept all the defaults so we can login from the backup server without having to enter in a password.

Copy ssh key to the server we are wanting to back up

sudo ssh-copy-id backupuser@ip

enter in the password and the the key should get copied it over. Once complete, verify that you can login without having to enter in a password.

Setup rsnapshot config (On backup server)

Open up the rsnapshot config file and modify where appropriate. /etc/rsnapshot.conf

Change the path to where the snapshots are stored. By default it stores them under /.snapshots. I moved it under a local user as I am not needing to use rsnapshot to backup the local backup server files.


# SNAPSHOT ROOT DIRECTORY
snapshot_root /home/user/rsnapshot/snapshots/

Add a daily backup option under Backup levels

# BACKUP LEVELS / INTERVAL #
retain daily 6

Setup remote server to get a backup from. Replace ipaddress and directories as needed. hostname is the sever name. You can change to whatever you want.

### BACKUP POINTS / SCRIPTS ###
# LOCALHOST
# Comment or delete entries unless you want to backup those as well
# EXAMPLE.COM
backup  backupuser@ipaddress:/home/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"

If you would like to back up multiple locations you can create multiple entries with different remote paths. Example locations to add

backup  backupuser@ipaddress:/etc/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"
backup  backupuser@ipaddress:/usr/local/     hostname/       +rsync_long_args=--rsync-path="sudo rsync"

Verify that the config is good with

sudo rsnapshot configtest

It should return Syntax OK

Setup Crontab

sudo crontab -e

Add the following line to run rsnapshot at 3AM every day. More information about crontab can be found here.

0 3 * * * /usr/bin/rsnapshot daily

Final Testing

Manually run a backup to verify everything is set up correctly.

sudo rsnapshot daily

After it runs you can check the directory you specified in the config file to verify that the files did get copied.

Enable Automatic Update for Ubuntu 20.04

Thankfully enabling automatic updates in Ubuntu is super easy.

First make sure that the “unattended-upgrades” package is installed

sudo apt install unattended-upgrades

It was already installed on my Ubuntu 20.04 server instance.
Next run dpkg to reconfigure and enable updates

sudo dpkg-reconfigure unattended-upgrades

You should get the following prompt.

Configuring automatic updates

Hit “Yes” to enable.

Your system should now automatically install updates. however, if it needs to reboot it may not. You can configure the reboot options in

sudo vi /etc/apt/apt.conf.d/50unattended-upgrades

Scroll down to the Reboot lines and uncomment

// If automatic reboot is enabled and needed, reboot at the specific
// time instead of immediately
// Default: "now"
Unattended-Upgrade::Automatic-Reboot-Time "02:00";  // <- Uncomment line

Save the file. Your system should now automatically install stable updates.

Disable automatic update

You can disable the automatic updates by running the dpkg command again.

sudo dpkg-reconfigure unattended-upgrades

and selecting “No”

Automatic updates should now be off.

More information can be found at the following link.

https://www.cyberciti.biz/faq/set-up-automatic-unattended-updates-for-ubuntu-20-04/