Linux Commands

Removing comments from config files

from 20-lmtp.conf as an example:

 grep '^[:blank:](:blank:)*[^[:blank:]#;]' 20-lmtp.conf

Installing a GPG key

Example:

 wget -O- https://download.webmin.com/jcameron-key.asc | sudo gpg --dearmor | sudo tee /usr/share/keyrings/jcameron-key.gpg > /dev/null 2>&1 

Then need to edit the sources.list file to look something like:

 deb [signed-by=/usr/share/keyrings/jcameron-key.gpg] https://download.webmin.com/download/repository sarge contrib

Change permissions for whole directory structure

For directories:

find /desired_location -type d -print0 | xargs -0 chmod 0755

For files:

find /desired_location -type f -print0 | xargs -0 chmod 0644

Adapt as required.

Delete all files with given pattern

 find . -name '*altauserpoints*' -print0 | xargs -0 -P0 rm

Adapt as required.

Make a change in every file in a directory

 sed -i 's/foo/bar/g' *

To make the change through a whole directory tree:

 find ~/public_html/my_website/pages -type f -exec sed -i 's/2017/2018/g' {} \;

Search within specific file type

 grep -ir removed --include="*.txt" .

will search files with extension .txt ignoring case (-i)

Bluetooth

Using this from the command line seems to do more than the GUI:

 bluetoothctl

Limiting journal log size

Edit the file:

 /etc/systemd/journald.conf

and set SystemMaxUse, for example

 SystemMaxUse=250M

Then restart journal with:

 systemctl restart systemd-journald

Checking Postfix config

 postfix check