Most of the notes in here are Arch Linux specific, as this is the distro I use most and the one which tends to give me the most curveballs to deal with! But this is what’s so good about it, as it gives me a way to learn things better than I would do with one of the more common distros like Ubuntu.

If anyone reads any of these notes and thinks there’s a better way, please let me know - any help is always appreciated. Maybe you’d prefer to submit a PR?


Useful file locations

These are a few files/paths I always forget because I rarely need to look at them when my Linux machine is working fine.

Location
Pacman logs/var/log/pacman.log
Pacman cache/var/cache/pacman/pkg/

Mounting the current installation from a live environment

I tend to keep my /home directory on a separate partition, so I do the following:

mkdir /mnt/root
mkdir /mnt/root/home

mount /dev/sda1 /mnt/root
mount /dev/sda3 /mnt/root/home

arch-chroot /mnt/root

This gives me the zsh shell logged in as root into my current Arch installation so I can do any diagnosis. Once I’m finished, I exit my installation, unmount and reboot.

exit
umount -R /mnt
reboot

Installing KDE and tools

plasma-desktop (The KDE desktop - seems to be referenced as plasma nowadays)

plasma-nm (NetworkManager for plasma/KDE - enable it through sudo systemctl enable NetworkManager)

kde-applications (gives you a bunch of KDE apps, konsole etc.)

kgpg (for encrypting the KDE wallet for wifi keys etc.)

powerdevil (configuring power settings and/or power savings)


UFW (Uncomplicated FireWall)

This is a pretty simple to configure firewall on Linux (I guess that’s where the Uncomplicated part of the name came from!)

It is typically installed on Ubuntu Server by default, but if not, you can install it through Aptitude:

sudo apt install ufw

Once you’ve got it installed, you can check the status…

$ sudo ufw status verbose
Status: inactive

And after this, making sure that SSH access is allowed…

$ sudo ufw allow ssh
Rules updated
Rules updated (v6)

you can enable it…

$ sudo ufw enable
Command may disrupt existing ssh connections. Proceed with operation (y|n)? y
Firewall is active and enabled on system startup

At any time you can see what apps are available to grant/block through the firewall (I don’t have many on mine so far!):

$ sudo ufw app list
Available applications:
  OpenSSH

Other commands:

CommandDescription
allow httpGrant http access over port 80
allow 80/tcpSame as above, but very explicit to the port and protocol
allow httpsGrants https access over port 443
allow 8000:8100/tcpGrant access on all ports between the specified range
allow from {ip}Grant access to all ports from a specified ip
allow from {ip} to any port 8000Grants access from the specific IP to port 8000
allow from 192.168.10.0/24 to any port 8000Grants access from any IP in the specified subnet to port 8000
deny from {(ip|subnet range)}Blocks access to any port from the specified IP or subnet range

Note: All allow rules can be deny rules by simply changing the wording.

Ok, so I’d like to delete some rules now… how would I do that?

Delete the rule by specifying what you added:

sudo ufw delete allow ssh

Or, you can list all the rules with associated IDs by getting the numbered status:

$ sudo ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22/tcp                     ALLOW IN    Anywhere
[ 2] 22/tcp (v6)                ALLOW IN    Anywhere (v6)

and then deleting the one you no longer want:

sudo ufw delete 2

Finally, want to disable UFW and reset it to defaults?

sudo ufw reset

MDADM (Mounting RAID devices)

This was from mounting the drive from a single disk Zyxel NSA310 NAS.

It appears the disk is actually in its own RAID array. Never seen this before!

Advice online suggested doing the following:

$ sudo mdadm --assemble --force /dev/md0 /dev/sdc2
mdadm: /dev/sdc2 is busy - skipping

So I had to figure out what was making the disk busy…

$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active linear sdc2[0]
      487868928 blocks super 1.2 0k rounding

unused devices: <none>

Ok, so it’s already configured and ready to go, so there must be a file in /dev/ for it…

$ ls /dev/md*
/dev/md127

/dev/md:
nsa310:0

Yup, there is one! So I just have to mount it now…

$ sudo mount /dev/md127 /mnt/nas

Works a treat!