Change service shutdown timeout in Debian

Make a change so that slow-non/responding services to terminate quickly during shutdown:

sudo nano /etc/systemd/system.conf

Uncomment and edit to:

DefaultTimeoutStopSec=5s

Reboot or reload with:

sudo systemctl daemon-reload

Change GRUB boot delay

sudo nano /etc/default/grub

sudo update-grub

Adding ufw rules using application profiles while restricting source network

Unfortunately, the ufw help doesn't provide an example for using application profiles while specifying the source network. Here's an example how "OpenSSH" profile can be used but restricting the source network to local:

sudo ufw allow from 192.168.0.0/24 to any app OpenSSH

Disable IPv6 in Debian Trixie

Edit /etc/hosts and remove the default IPv6 entries, including localhost, etc. If you don't do this, you may encounter weird errors down the road because some programs will try to bind to "localhost" and it ends up try using non-existing IPv6 address, etc.

Create the follow file:

sudo nano /etc/sysctl.d/90-disable_ipv6.conf

then add these lines and save:

net.ipv6.conf.all.disable_ipv6 = 1

net.ipv6.conf.default.disable_ipv6 = 1

Run:

sudo sysctl --system

Jumbo frame size setting in Windows

For network adapter drivers that require the "Jumbo Packet" value to be set for MTU, enter 9014. This is to accommodate 14 bytes of Ethernet header, which is then added to the 9000-byte packet. For example, Mellanox ConnectX-3 adapters require this value to function correctly.

To confirm testing of Jumbo frame between two nodes, use the ping command as follows:

For Windows:

ping <target> -f -l 8972

For Linux:

ping <target> -M do -s 8972

Upgrade to Debian 13 (trixie)

sudo apt update

sudo apt upgrade

sudo sed -i 's/bookworm/trixie/g' /etc/apt/sources.list

sudo apt update

sudo apt upgrade

sudo reboot

Disable Proxmox firewall temporarily

When you mess up the Proxmox firewall setup and you can't access the server...

pve-firewall stop

This stops the firewall until next reboot or update of any packed what restart the pve-firwall.

If you like to disable it permanently , you can do this in the /etc/pve/firewall/cluster.fw

set enable: 1 to 0

Citation: https://forum.proxmox.com/threads/disable-firewall-from-command-line.29091/