Log denied connections in firewalld
Edit file /etc/sysconfig/firewalld:
FIREWALLD_ARGS=--debug=10
linux/
Debug route table
List all routes in system:
route -n
Get route for a specific IP:
ip route get 1.1.1.1
Run command on suspend
Create a file located in /usr/lib/systemd/system-sleep directory:
#!/bin/sh
if [ "${1}" == "pre" ]; then
nordvpn d
elif [ "${1}" == "post" ]; then
echo "Hello"
fi
Log executed command
14:27 $ (set -x; sleep 1 && sleep 2)
+ sleep 1
+ sleep 2
Wait until able to connect
while ! nc -w5 -z 10.0.0.100 22; do echo "hello"; done
Dell Precision 5540 - Battery drains in sleep mode
Run the following command to check the suspend mode:
cat /sys/power/mem_sleep
If the output looks like this:
[s2idle] deep
It means that very inefficient suspend mode is active (drains battery from 100% to 0 in 9 hours). To enable “deep” mode, edit file /etc/default/grub and append mem_sleep_default=deep to GRUB_CMDLINE_LINUX:
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet mem_sleep_default=deep"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true
Apply changes:
sudo grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
Restart your laptop and verify changes:
$ cat /sys/power/mem_sleep
s2idle [deep]
fedora: Lockdown a kernel version
Fedora typically keeps 3 latest kernel versions. However, what if you want to keep an old specific kernel version which is known to work well with your system? First, we need to install a dnf plugin that allows us to keep a specific version of any package:
sudo dnf install python3-dnf-plugins-extras-versionlock
Lets find all available kernel versions for your system:
sudo dnf list kernel --showduplicates
Install that specific version of the kernel:
sudo dnf install kernel-5.3.7-301.fc31
And lock it:
sudo dnf versionlock add kernel-5.3.7-301.fc31
To remove the lock:
sudo dnf versionlock delete kernel-5.3.7-301.fc31
Check and modify mtu of a connection
To check:
[root@lxd-node3 ~]# netstat -i
Kernel Interface table
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
ens10 1450 455 0 0 0 671 0 0 0 BMRU
eth0 1500 28 0 0 0 32 0 0 0 BMRU
lo 65536 0 0 0 0 0 0 0 0 LRU
Modify temporarily:
ifconfig eth0 mtu 1450
Permanently: edit /etc/sysconfig/network-scripts/ifcfg-eth0 file and add:
MTU=1450
Might be the reason why the system can establish HTTP connection but HTTPS
Useful wifi commands
List used wifi frequencies
sudo iwlist wlp1s0 scan | grep Frequency | sort | uniq -c | sort -n
List available channels
iwlist channel
List wifi networks
nmcli d wifi