---
title: 'Linux Commands'
url: 'https://manuals.remository.com/useful/linux-commands'
markdown: 'https://manuals.remository.com/useful/linux-commands.md'
date: '2026-10-06'
description: "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 > …"
---

[](#) [ edit this page](https://github.com/getgrav/grav-skeleton-rtfm-site/blob/develop/pages/04.linux-commands/chapter.md) 

# 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
```

---

## Navigation

- Previous: [Database](https://manuals.remository.com/useful/database.md)
- Next: [Mikrotik and Ubiquiti](https://manuals.remository.com/useful/mikrotik-and-ubiquiti.md)