Merge branch 'master' into vhs

basics/hard_links.md

@@ -0,0 +1,38 @@
+---
+title: "hard links"
+tags: [ "basics", "links" ]
+---
+
+A hard link is one file which exists in multiple locations.
+
+Each file has an ID, which is kept on the hard disk's partition.
+Each hard link has the same ID, because they are the same file.
+This ID is called the 'inode'.
+
+Create a file, and a hard link:
+
+```bash
+fortune > $file_1
+mkdir -p x/y/z/
+ln $file_1 x/y/z/$file_2
+```
+Have a long look at the file with the `-l` flag, and check the inode with `-i`:
+
+```bash
+ls -li $file_1 x/y/z/$file_2
+```
+
+Since they are the same file, you can make a change to one, and it changes both:
+
+```bash
+fortune | tee x/y/z/$file_2
+cat $file_1
+cat x/y/z/$file_2
+```
+
+# Danger Zone
+
+- hard links will not work on directories, only standard files and fifos.
+- `git` will destroy and remake files, so it will not respect hard links.
+- Files cannot have a hard link on another disk partition, because the inode is stored on each partition.
+

basics/links.md

@@ -1,19 +1,9 @@
 ---
 title: "links"
-tags: [ "Documentation", "Basics" ]
+tags: [ "basics", "links" ]
 ---
-Link from X to Y.
 
-```bash
-ln -s X ../otherdir/Y
-```
-
-If you want a hard link, this will make a single file exist in two locations.
-If it is deleted in one location, it continues to exist in the other.
-
-```bash
-ln *X* *Y*
-```
-
-Both files must be on the same hard drive, as they have the same inode (check this with `ls -i file`).
+There are two types:
 
+- [Soft links](soft_links.md)
+- [Hard links](hard_links.md)

basics/soft_links.md

@@ -0,0 +1,72 @@
+---
+title: "soft links"
+tags: [ "basics", "links" ]
+---
+A soft link is a file which says how to go to another file.
+When a program encounters a soft link, it will make a  guess at whether it should ignore it, or try to get to that file.
+
+To make a soft link to a file in the current directory, linking is easy:
+
+```bash
+fortune > $file_1
+ln -s $file_1 $link_1
+```
+
+Now imagine your directory looks like this:
+
+```
+dir_0/
+├── dir_1
+│   └── file_1
+├── dir_2
+│   └── file_1
+├── file_1
+└── link_1
+
+```
+
+Inside `dir_1`, making a soft link to `dir_0/file_1` would mean putting the directions to that file:
+
+```bash
+cd dir_1
+ln -s ../file_1 link_1
+```
+
+The real content of the file is just '`../file_1`, so making it from another directory would mean writing exactly the same address to that file:
+
+```bash
+ln -s ../file_1 dir_2/link_2
+```
+
+Both symlinks are identical, except for the name.
+
+```
+dir_0/
+├── dir_1
+│   ├── file_1
+│   └── link_1   <-- This one points to ../file_1
+├── dir_2
+│   ├── file_1
+│   └── link_2   <-- This one points to ../file_1 as well.
+└── file_2
+
+```
+
+Since it's just an address, you can delete the original file, then make another.
+
+```bash
+rm file_1
+ls -l dir_1/
+fortune > file_1
+cat dir_2/link_2
+fortune | tee -a file_1
+cat dir_1/link_1
+```
+
+Last, let's make a link from `dir_2/link_2` to `dir_1/file_1` (this will delete the old link):
+
+```bash
+ln -s -f ../dir_1/file_1 dir_2/link_2
+cat dir_2/link_2
+```
+

basics/time.md

@@ -68,3 +68,11 @@ ntpq -p
 
 Usually this is run as a service, so just start that service.
 
+# Force Reset
+
+If your clock drifts too far from the right time, it will not reset happily.
+For it to reset like this:
+
+```bash
+sudo ntpd -q -g -x -n
+```

data/exiftool.md

@@ -22,6 +22,7 @@ And overwrite all metadata:
 ```bash
 exiftool -all= -overwrite_original -ext jpg .
 ```
+(NB: This does not work on pdf data. See [here](pdf_erasure.md) for erasing all pdf data)
 
 Or just GPS data:
 
@@ -36,3 +37,4 @@ identify -verbose
 ```
 
 
+

data/pdf_erasure.md

@@ -0,0 +1,25 @@
+---
+title: "PDF Metadata Erasure"
+tags: [ "Documentation", "Metadata", "Ghost Script" ]
+---
+
+Make a text file called 'pdfmark.txt'.
+
+
+```text
+[ /Title ()
+/Author ()
+/Subject ()
+/Creator ()
+/ModDate ()
+/Producer ()
+/Keywords ()
+/CreationDate ()
+/DOCINFO pdfmark
+```
+
+Then run:
+
+```bash
+gs -o output.pdf -sDEVICE=pdfwrite "$FILE".pdf pdfmark.txt
+```

system/deduplicate.md

@@ -0,0 +1,19 @@
+---
+title: "deduplicate"
+tags: [ "system", "deduplicate", "duplicates", "maintenance" ]
+---
+
+`rdfind`: find duplicate files, then delete them, or turn them into links.
+
+Ask if a directory has duplicates (`rdfind` will not delete anything):
+
+```bash
+rdfind $dir
+$EDITOR results.txt
+```
+
+Replace the duplicated files with [hard links](../basics/hard_links.md).
+
+```bash
+rdfind -makehardlinks true $dir
+```