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---
title: "Useful Commands"
visible: true
---
[toc]
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## Imagemagick
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### Splitting PDF files
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```sh
convert -density 600 {INPUT.PDF} -crop 50x100% +repage {OUT.PDF}
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```
```
-density: adjusts the quality of the resulting pdf. Higher values look better, but take longer to process
-crop 50x100%: this splits the pdf into "left" and "right". 100x50% would split into "top" and "bottom"
```
## Find
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### Change filtered permissions
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Using find with its `exec` switch one can set different permissions based on the usual find filters.
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One example would be only changing file or directory permissions.
```sh
find (directory) -type f -exec chmod 744 {} +
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```
Replacing `-type f` with `-type d` would execute the `chmod` for directories instead.
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## Various
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### Overwrite disk with pseudorandom data
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Using openssl on CPUs with AES acceleration one can create pseudorandom data with high speeds.
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Much faster than `/dev/urandom` at least
```sh
openssl enc -aes-128-ctr -md sha512 -pbkdf2 -nosalt -pass file:/dev/urandom < /dev/zero | pv > {TARGET DISK}
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```
Around 2GiB/s on my Ryzen 7 1700x if output to `/dev/null`
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### Formatted csv in terminal
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> [From Pretty CSV viewing on the Command Line](https://www.stefaanlippens.net/pretty-csv.html)
```sh
column -t -s, < {FILE.CSV}
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```
### Download directory from webdav
Using `wget`, it's possible to download directories recursively from WebDAV.
```sh
wget -r -nH -np --cut-dirs=1 --user={USERNAME} --password={PASSWORD} https://WEBDAVHOST/DIR/DIR
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```
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### Find USB speed in use
First, the USB device you want to check has to be selected
[shuser]
```sh
lsusb
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(out)Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
(out)Bus 003 Device 003: ID 0c45:652f Microdia Backlit Gaming Keyboard
(out)Bus 003 Device 002: ID 046d:c084 Logitech, Inc. G203 Gaming Mouse
(out)Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
(out)Bus 002 Device 002: ID 0781:55a3 SanDisk Corp. SanDisk 3.2Gen1
(out)Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
(out)Bus 001 Device 002: ID 2972:0047 FiiO Electronics Technology FiiO BTR5
(out)Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
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```
[/shuser]
Now, using the ID, the USB class used can be determined
[shuser]
```sh
lsusb -d 0781:55a3 -v | grep bcdUSB
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(out)bcdUSB 3.20
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```
[/shuser]