Linux tips and tricks

Empty files content from command line

truncate -s 0 *.log
cat /dev/null > file.log

Shutdown Linux Ubuntu computer

here are the commands available to poweroff (not halt) a computer:

sudo poweroff
sudo shutdown -h now
sudo shutdown -P now
sudo halt -p
sudo init 0

shutdown -P now = poweroff or halt -p

init 0 = runlevel 0 (shut down)

shutdown forcefully:

sudo poweroff -f

Change sh to bash on Ubuntu

$ls -l `which sh`
/bin/sh -> dash

$sudo dpkg-reconfigure dash #Select "no" when you're asked

$ls -l `which sh`
/bin/sh -> bash

Crontab to Power Off computer

$ crontab -e
*/30 * * * * HOUR=$(date +%H); if [ $HOUR -ge 21 ] || [ $HOUR -le 7 ]; then echo "$(date): poweroff..." >> /tmp/log/poweroff.log && poweroff; fi

Remove grayed out input method menu item

$sudo apt install dconf-editor
# edit org.gnome.desktop.input-sources

How to cancel Update Manager downloading flashplugin-installer

ps aux | grep http

This will result in 2 or 3 lines with the second column of each line being the pid of the process if the process is doing its job

Kill this process by running:

kill -9 pid

How to resume or abandon an apt dist-upgrade after connection reset

ps -aux | grep apt
kill -9 pid

Configure previously already installed packages:

dpkg --configure --pending

If you are unable to continue because the system is broken, you could try to fix it with apt:

apt --fix-broken install

Unable connect to wifi after upgrade to Ubuntu 18.04

#work around DNS resolv bug
systemctl stop systemd-resolved
sed -i 's/#DNS=/DNS=' /etc/systemd/resolved.conf

#sed -i 's/#Domains=/' /etc/systemd/resolved.conf

systemctl start systemd-resolved
systemctl restart NetworkManager
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