Debian

Package installation

dpkg

Install a package from a .deb file

sudo dpkg -i PACKAGE_NAME

Remove a package

sudo dpkg -r PACKAGE_NAME

Purge a package

This removes the package and all its dependencies

sudo dpkg -P PACKAGE_NAME

List installed packages

dpkg -l

Lookup information on a hostname

dig domain_to_lookup

Cron jobs

Edit cronjobs

To edit cron jobs use crontab -e. The syntax is as follows

[Minute] [hour] [Day_of_the_Month] [Month_of_the_Year] [Day_of_the_Week] [command]

So a valid cron job could look like this, runs everyday at 2am

0 2 * * * /bin/sh backup.sh

To run on an interval (in this case every 10 minutes), use

*/10 * * * * /scripts/monitor.sh

List cron jobs

crontab -l

File movement

Copy files from directory into another

cp -a /source/. /dest/

Move files into parent directory

mv subfolder/* .

Web hosting

Give permissions to a user to use /var/www for static files

See this post for a good summary of things to watch for. For static files there shouldn't be anything that needs to be written by the webserver.

sudo gpasswd -a "$USER" www-data
sudo chown -R "$USER":www-data /var/www
find /var/www -type f -exec chmod 0640 {} \;
sudo find /var/www -type d -exec chmod 2750 {} \;

Can then confirm permissions with

ls -la

Localhost

Kill a process running on localhost

First, find the process using

lsof -i :3000

Then, kill the process via the PID

kill <PID> 

User management

Create a new user with sudo

Create the new user. Need to use sudo if not signed in as root.

adduser <newuser>

Give sudo priveleges

usermod -aG sudo <newuser>

Useful terminal commands

cmp - Compares to see if two files are equivalent

Create a RAID array

For a full article, reference How To Create RAID Arrays with mdadm on Ubuntu

Find existing RAID information

cat /proc/mdstat

If there is an existing array, it needs to be unmounted from the filesystem

sudo umount /dev/md0

Stop and remove the array

sudo mdadm --stop /dev/md0

Look at existing disk structure

lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Create the array (this example is for RAID 5)

sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda /dev/sdb /dev/sdc

Check the progress

cat /proc/mdstat

Create the filesystem on the array

sudo mkfs.ext4 -F /dev/md0

Create the mountpoint

sudo mkdir -p /mnt/md0

Mount

sudo mount /dev/md0 /mnt/md0

Check that the expected space is available

df -h -x devtmpfs -x tmpfs

Save the array layout

Make the array reassemble on boot (adjust the /etc/mdadm/mdadm.conf)

sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf
sudo update-initramfs -u # Update initial RAM system
echo '/dev/md0 /mnt/md0 ext4 defaults,nofail,discard 0 0' | sudo tee -a /etc/fstab

Generate a random value (useful for secret keys)

openssl rand -hex 32