Show system time:

1date

Show hardware time:

1sudo hwclock -r

Change system time to match hardware time:

1sudo hwclock --hctosys

Change hardware time to match system time:

1sudo hwclock --systohc

Manually set the hardware time to a specified date:

1sudo hwclock --set --date="8/25/19 13:30:00"

Normal Date

1date …

If statements

Test statement equality as so:

1
2read t1
3read t2
4if test $t1 != $t2; then
5	echo 'variables do not match'
6else
7	echo 'variables match'
8fi
9exit 0

Case Structure

These deal with multiple states rather than forking conditions.

Example:

 1
 2#!/bin/bash
 3
 4# Simple case demonstration …

Cronie

The cronie program is also known as crond.

Install

1sudo apt search -n ^cron

Once installed, search for the service name, and start it.

1sudo systemctl list-unit-files | grep cron
2sudo systemctl enable --now $NAME

Usage

Show your current crontab:

1crontab -l

You can put this in a file and edit it:

1crontab -l …

Install the package xdg-utils, then make very liberal use of the tab button.

Ask

Ask what type of application opens an mkv file:

1xdg-mime query default video/mkv

Same with pdf:

1xdg-mime query default application/pdf

Ask what file-type book.pdf uses.

1xdg-mime query filetype *book.pdf*

Set

Set the mime type of mp4 …

1sudo pacman -S docker

1sudo usermod -aG docker $USER

1sudo systemctl start docker

You need to either log out and back in again to be in the docker group, or run everything as root.

1# docker info

This should show you things are working.

Search for a distro you want

1docker search debian

If you get a hit, pull it.

1 …

Install yt-dlp.

1yt-dlp --write-auto-sub *<URL>*

It will default to English, but you can specify another language with the flag --sub-lang:

1youtube-dl --sub-lang sv --write-auto-sub *<URL>*

You can list all available subtitles with:

1yt-dlp --list-subs *<URL>*

It's also possible to skip the video and …

Set up a file like this, called troubleshooting.txt.

[ Is there an IP address? ] -- no --> [ Check NIC driver, dmesg ]

[ Is there an IP address? ] -- yes --> [ Can you ping the router? ]

[ Can you ping the router? ] -- no --> [ Check cables, router, and switches ]

[ Can you ping the router? ] -- yes --> [ …

Find metadata.

1exiftool image.jpg

Find info on all images in current directory.

1exiftool -ext .png .

You can make this recurring with the -r switch.

And overwrite all metadata:

1exiftool -all= -overwrite_original -ext jpg .

(NB: This does not work on pdf data. See here for erasing all pdf data)

Or just GPS data:

1 …

Monitor all processes:

1extrace

Monitor one process:

1extrace ls

Monitor a script:

1./script.sh | extrace

SSH Daemon Jail

1sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.d/ssh.local

1[sshd]
2enabled = true
3
4ignoreip = 127.0.0.1/8 ::1,192.168.0.0/16 ::1

1sudo systemctl restart fail2ban

1sudo fail2ban-client status

1sudo fail2ban-client status sshd