Difference between revisions of "Main Page"

Latest revision as of 16:34, 9 July 2021

Welcome to the PaskvilWiki!

The future shape of this wiki is unknown for now, let's hope it'll be something good...

This is partially a private wiki - viewing is allowed to all, but editing is allowed only to registered users.

This is more of a prevention than denial - I don't have time to monitor and moderate edits; - you're more than welcome to request registration, all contributors are very much welcome!

Just write me at josef.at.paskvil.dot.com.

References and Tutorials

Emacs and Slime Reference

Small jQuery Reference

Small jQuery Cheat Sheet

Small SPARQL, RDQL, etc. Cheat Sheet

Short Notes - Tips and Tricks

4store

setup and installation
running 4store
data import
data import and querying from Python
Turtle file printer (in Python)

Apache

Note on serving of local files
Self-Signed SSL Certificate
Enable SSL/HTTPS in Apache
.htaccess and mod_rewrite Tricks

AWS

Debugging (lack of) connection to instance
Authorization header being removed by ElasticBeanstalk
Notes on IAM
AWS Lambda with Python - Notes
boto3 Snippets
AWS Chalice
Building a Python Layer

Bash

Extensions and File Name
File Test Operators
Commands and Shortcuts

$ sudo !!                         - run last command as root
$ !!:gs/foo/bar                   - run last command, replacing 'foo' with 'bar'
$ ^foo^bar                        - run last command, replacing 'foo' with 'bar'
$ cp filename{,.bak}              - create a .bak copy of file
<Ctrl-x> <Ctrl-e>                 - open $EDITOR to edit current command line; upon exit, content will be run
$ <space>command                  - run the command without saving it in history
$ > file.txt                      - empty a file
<Alt+.>                           - put last argument on cursor place; repeat to cycle through
$ (cd /tmp && ls)                 - jump to /tmp, execute ls, and jump back here
$ pushd /tmp .... $ popd          - goes to /tmp, remembering current location; at later time, popd will bring you back
$ \command                        - run command without using aliases
$ rm !(pattern|pattern)           - delete files that do not match given patterns
$ find . -mtime +5 -exec rm {} \; - delete all files in this folder that are older than 5 days
<Ctrl-u> ... <Ctrl-y>             - Ctrl+u will cut current command, then you can do whatever you need, and Ctrl+y will paste it back
$ date -d @1234567890             - convert unix timestamp to human-readable
$ jul () { date -d "$1-01-01 +$2 days -1 day" "+%Y%m%d"; }   - `jul $year $daynum` prints $daynum's day of $year, with Jan 1st being day 1

Informations

$ mount | column -t               - pretty-print mount table
$ cat /etc/issue                  - display distro name

Small Tricks

$ echo $(printf '%q' "A\"B")      - prints escaped string (in this case, > A\"B <)
$ mount -t tmpfs tmpfs /mnt -o size=1024m      - mount temporary RAM partition (fast access, non-persistent!)
$ disown -a && exit               - exit the shell while keeping all running processes alive
$ ssh -t remote_host screen -r    - directly connect to a remote screen process
$ for I in $(mysql -e 'show databases' -s --skip-column-names); do mysqldump $I | gzip > "$I.sql.gz"; done
                                  - backup all databases into individual files
$ fuser -k filename               - kill process that is locking given file
$ readom dev=/dev/scd0 f=/path/to/image.iso    - create CD/DVD ISO image
$ diff -rq folder-1 folder-2      - compare 2 folders (files missing or differing)
$ mkdir -p a/deep/dir/tree        - create nested directories fast
$ mount file.iso /mnt/iso -o loop - mount ISO file as drive /mnt/iso (dir has to preexist)
$ sudo touch /forcefsck           - force a file system check on the next reboot
$ ls | while read f; do process_file "$f"; done    - iterate through files even if they contain space in name
$ while read f; do process_file "$f"; done < <(ls) - iterates through files, but does not create sub-process (outside scope is visible)

lsof

$ lsof -nPi                       - list network connections
$ netstat -tlnp                   - print all listening ports with PID's (run as root to see all process names)
$ lsof -c gnome-terminal          - list files opened by given command
$ lsof +D [folder]                - discover all open files in the [folder]
$ lsof -p [pid]                   - list files opened by given PID
$ lsof -i :8080                   - list programs that have port 8080 open ("who to kill" if you get "port already in use")
$ if [ `lsof -- file | wc -l` -ne 0 ] ... - tests if file is open by some process

C/C++

How to clean up after child thread
Non-blocking IO using sockets
Shared Libraries on Linux+GCC
Singleton
std::move Semantics
Converting between std::string and std::wstring in C++11

cURL (in terminal)

Use -s option to make curl silent.

POST to server using cURL:

curl --data "key1=value1&key2=value2" http://www.example.com/post.php

Upload to FTP server (with credentials), having connection timeout 60 seconds, and 120 seconds maximum operation time:

curl --connect-timeout 60 -m 120 -T file.ext "ftp://12.34.56.78/folder" --user user:pass

Download from FTP server (with credentials):

curl --user user:pass "ftp://12.34.56.78/folder/file.ext" -o ~/Downloads/file.ext

Docker

ElasticSearch

Installation
What You Get
Indexing, Routing, etc.
Deleting
Getting and Multi-Getting
Updating
Search and Query DSL

ffmpeg

process all files, may include spaces in file name:

ls *.avi | while read f; do ffmpeg -i "$f" ...params... "$f.mkv"; done

if you're having problems with input format, passing video through mpeg typically helps:

ffmpeg -i file.mkv -qscale 2 -f mpeg - | ffmpeg -i - ...params... file.avi

downmix 5.1 dolby to normal stereo:

ffmpeg -i file.mkv ...params... -acodec libmp3lame -ar 44100 -ac 2 file.avi

add an overlay image to the video:

ffmpeg -i input.mp4 -i image.png -filter_complex "[0:v][1:v] overlay=x:y:enable='between(t,0,20)'" -pix_fmt yuv420p -c:a copy output.mp4

This will add image.png as an overlay at position x, y over the imput.mp4 video, for the first 20 seconds.

fade in and out, first and last 25 frames of a 1000 frame video

ffmpeg -i input.mp4 -vf "fade=in:0:25,fade=out:975:25" -acodec copy out.mp4

convert album contained in APE or similar file with CUE into separate MP3 tracks

ffmpeg -i cd.ape -ab 256k cd.mp3
mp3splt -a -c cd.cue cd.mp3

more on ffmpeg

Rip DVD into FLV (or anything else)
Video File with Still Image and Audio
Concatenate Videos

Flask and Flask-RestPlus

git

All things JS - React, Vue, ...

Kyoto Cabinet and Kyoto Tycoon

Setup and Install Kyoto Cabinet
Setup and Install Kyoto Tycoon
KT's RPC API Reference

Linux Administration

Reset Compiz to Default Settings
Enable and Start sendmail
Installing sendmail
Sending Emails using sendmail
Find and Mark Bad Blocks
Using TLP to optimize battery lifetime

MAC OSX

Asynchronous Execution
- NSThread
- performSelectorInBackground
- dispatch_async
MacPorts

$ sudo port selfupdate
$ sudo port upgrade outdated
$ sudo port uninstall inactive
$ (just once) sudo port install port_cutleaves
$ sudo port_cutleaves

MongoDB

Installation on Ubuntu
Troubleshooting on Desktop
Use in PHP via PECL driver

MySQL

Error 1045: Access denied
The insert ... on duplicate key update Pitfall
Shrink ibfile1 InnoDB File
Index JSON columns

PDF

Merging PDF Files using GhostScript
Cutting PDF Files using GhostScript
Converting to PDF using GhostScript

PHP

Convert Accented Characters to Non-Accented
Upload a File using cURL
HTTP Post in Pure PHP (without cURL)
Prevent Client Disconnect from Killing PHP
Disconnect Client and Continue Processing

PSQL, Postgres, PostgreSQL

Dump and Restore
Delete Duplicate Rows
Set Sequence Value to Max of Table's ID

Python

Timing, and memory, on Linux
Importing Files
uWSGI, nginx, Flask
Decorators
virtualenv
SQLAlchemy
iPython fails with NameError: name 'sys' is not defined on autocompletion

RedBeanPHP Cheat Sheet

RESTful APIs

Security

Password Generators
SSH Access using pubkey's Authentication
Using RSync together with SSH

Subversion/SVN

Simple Guide to SVN Client
Creating a SVN Repository
Moving a SVN Repository
Change Repository URL (Subversion 1.7+)
Setup a SVN Server on a Shared Hosting with no root Access
creating and applying patch (the --diff-cmd is necessary in case you set some graphical diff-viewer in ~/.subversion/config):

cd root_of_project
svn di --diff-cmd diff > ~/patch.diff
cd root_of_other_project
patch -p0 -i ~/patch.diff

svn:externals - pull repo1 into dir1, and repo2 into dir2:

echo -e 'dir1 svn://repo1\ndir2 svn://repo2' > repos.txt
svn propset svn:externals . -F repos.txt

validate with " svn propget svn:externals . " .

Ubuntu / Debian / Gnome etc.

restrict gnome app switcher to current workspace only:

gsettings set org.gnome.shell.app-switcher current-workspace-only true

restore or undelete (config) file or directory:

# 1. check what package file or folder belongs to
$ dpkg -S /path/my.conf
# 2.a replace the config file; if it exists, will offer diff
$ sudo apt-get -o Dpkg::Options::="--force-confask" install --reinstall <package-name>
# 2.b restore the directory
$ sudo apt-get -o Dpkg::Options::="--force-confask" install --reinstall $(dpkg -S /etc/some/directory | sed 's/,//g; s/:.*//')

increase number of inotify watchers

$ cat /proc/sys/fs/inotify/max_user_watches 
8192
$ echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf
$ sudo sysctl -p
$ cat /proc/sys/fs/inotify/max_user_watches 
524288

Up-to-Date Versions of Packages

Python

Ubuntu 18.04 ships with Python 3.6, but Amazon Linux uses 3.7, so e.g. to use and build Lambda layers and match those against packages you deploy, you need to install 3.7:

$ sudo add-apt-repository ppa:deadsnakes/ppa
$ sudo apt update
$ sudo apt install python3.7 python3.7-venv

Since these do not override default python and python3 links (and better not!), you should create corresponding venv's as:

$ python3.7 -m venv [env-dir]

NPM, node.js, etc.

The default apt npm version is awfully outdated.

update - available as a snap as well, no need to add apt sources - https://node.dev/node-binary

Add NodeSource APT repo; for other versions, e.g. 12.x, change to setup_12.x.

$ curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
$ sudo apt update
$ sudo apt install nodejs

ViM

Delete all lines matching a pattern
Directly type HTML entities
Reformat a plain text paragraph

$ vim -x filename                      - open filename for editing, and save it encrypted (will prompt for a key)
:X                                     - set encryption for current file; use ':set key=' to disable encryption
                                       - put "set cm=blowfish" in your .vimrc to enable safer encryption by default
$ vim +10 [file] ; vim +/hello [file]  - open [file] at line 10, or at first occurrence of pattern 'hello' in file
:w !sudo tee %                         - save file via `sudo` (as root)

Wavelets

Integer Haar Wavelets in Python

Web - HTML, CSS, JS, jQuery, etc.

Multiple Submit Buttons and/or Multiple Forms on Page
Make 'float' Elements Appear One under Another
Upload a File via Form
Override the IE's Problem with width
Make an Element Fill In All the Remaining Space

Other Short Notes

Rip Video DVD that is not Finalized

Install Apache and PHP to do Secure h264 Pseudo Streaming

HTTP Response Codes

This is not a definitive list, it's just stuff I use the most, and always forget which is which.

100 - Continue
200 - OK
201 - Created
202 - Accepted
204 - No Content
301 - Moved Permanently
302 - Found (I typically use this instead of the 307 "Temporary Redirect")
304 - Not Modified
400 - Bad Request
401 - Unauthorized
403 - Forbidden
404 - Not Found
405 - Method Not Allowed (using GET on POST calls, etc. - must include "Allow" response header)
406 - Not Acceptable (mismatch of response format and "Accept" headers)
500 - Internal Server Error
501 - Not Implemented
503 - Service Unavailable

@@ Line 8: / Line 8: @@
 Just write me at josef.at.paskvil.dot.com.
-== SVN ==
-=== [[Simple Guide to SVN Client]] ===
-Bullets on how to use SVN client.
-=== [[Creating a SVN Repository]] ===
-How to create a new SVN repository to serve using <tt>svnserve</tt>, via <tt>svn+ssh</tt> or via Apache.
-=== [[Moving a SVN Repository]] ===
-Moving complete SVN repository from one host to another.
-=== [[Setup a SVN Server on a Shared Hosting]] ===
-How to setup SVN hosting (via <tt>svn+ssh</tt>) if you're on a shared hosting client - no root access.
 == References and Tutorials ==
@@ Line 34: / Line 20: @@
 == Short Notes - Tips and Tricks ==
+=== [[Small 4store How-To|4store]] ===
+* setup and installation
+* running 4store
+* data import
+* data import and querying from Python
+* Turtle file printer (in Python)
 === [[Short Notes on Apache|Apache]] ===
@@ Line 41: / Line 35: @@
 * Enable SSL/HTTPS in Apache
 * <tt>.htaccess</tt> and <tt>mod_rewrite</tt> Tricks
+=== [[Short Notes on AWS|AWS]] ===
+* Debugging (lack of) connection to instance
+* Authorization header being removed by ElasticBeanstalk
+* Notes on IAM
+* AWS Lambda with Python - Notes
+* boto3 Snippets
+* AWS Chalice
+* Building a Python Layer
 === [[Short Notes on Bash|Bash]] ===
 * Extensions and File Name
+* File Test Operators
+* ''Commands and Shortcuts''
 <pre>$ sudo !!                         - run last command as root
 $ !!:gs/foo/bar                   - run last command, replacing 'foo' with 'bar'
 $ ^foo^bar                        - run last command, replacing 'foo' with 'bar'
 $ cp filename{,.bak}              - create a .bak copy of file
-Ctrl-x Ctrl-e                     - open $EDITOR to edit current command line; upon exit, content will be run
+<Ctrl-x> <Ctrl-e>                 - open $EDITOR to edit current command line; upon exit, content will be run
 $ <space>command                  - run the command without saving it in history
 $ > file.txt                      - empty a file
-Alt+.                             - put last argument on cursor place; repeat to cycle through
+<Alt+.>                           - put last argument on cursor place; repeat to cycle through
-$ mount | column -t               - pretty-print mount table
-$ netstat -tlnp                   - print all listening ports with PID's
-$ mount -t tmpfs tmpfs /mnt -o size=1024m      - mount temporary RAM partition (fast access, non-persistent!)
 $ (cd /tmp && ls)                 - jump to /tmp, execute ls, and jump back here
-$ disown -a && exit               - exit the shell while keeping all running processes alive
 $ pushd /tmp .... $ popd          - goes to /tmp, remembering current location; at later time, popd will bring you back
-$ lsof -P -i -n                   - list network connections
-$ cat /etc/issue                  - display distro name
 $ \command                        - run command without using aliases
 $ rm !(pattern|pattern)           - delete files that do not match given patterns
+$ find . -mtime +5 -exec rm {} \; - delete all files in this folder that are older than 5 days
+<Ctrl-u> ... <Ctrl-y>             - Ctrl+u will cut current command, then you can do whatever you need, and Ctrl+y will paste it back
+$ date -d @1234567890             - convert unix timestamp to human-readable
+$ jul () { date -d "$1-01-01 +$2 days -1 day" "+%Y%m%d"; }   - `jul $year $daynum` prints $daynum's day of $year, with Jan 1st being day 1</pre>
+* ''Informations''
+<pre>$ mount | column -t               - pretty-print mount table
+$ cat /etc/issue                  - display distro name</pre>
+* ''Small Tricks''
+<pre>$ echo $(printf '%q' "A\"B")      - prints escaped string (in this case, > A\"B <)
+$ mount -t tmpfs tmpfs /mnt -o size=1024m      - mount temporary RAM partition (fast access, non-persistent!)
+$ disown -a && exit               - exit the shell while keeping all running processes alive
+$ ssh -t remote_host screen -r    - directly connect to a remote screen process
+$ for I in $(mysql -e 'show databases' -s --skip-column-names); do mysqldump $I | gzip > "$I.sql.gz"; done
+                                  - backup all databases into individual files
 $ fuser -k filename               - kill process that is locking given file
 $ readom dev=/dev/scd0 f=/path/to/image.iso    - create CD/DVD ISO image
+$ diff -rq folder-1 folder-2      - compare 2 folders (files missing or differing)
 $ mkdir -p a/deep/dir/tree        - create nested directories fast
-$ mount file.iso /mnt/iso -o loop - mount ISO file as drive /mnt/iso (dir has to preexist)</pre>
+$ mount file.iso /mnt/iso -o loop - mount ISO file as drive /mnt/iso (dir has to preexist)
+$ sudo touch /forcefsck           - force a file system check on the next reboot
+$ ls | while read f; do process_file "$f"; done    - iterate through files even if they contain space in name
+$ while read f; do process_file "$f"; done < <(ls) - iterates through files, but does not create sub-process (outside scope is visible)</pre>
+* ''lsof''
+<pre>$ lsof -nPi                       - list network connections
+$ netstat -tlnp                   - print all listening ports with PID's (run as root to see all process names)
+$ lsof -c gnome-terminal          - list files opened by given command
+$ lsof +D [folder]                - discover all open files in the [folder]
+$ lsof -p [pid]                   - list files opened by given PID
+$ lsof -i :8080                   - list programs that have port 8080 open ("who to kill" if you get "port already in use")
+$ if [ `lsof -- file | wc -l` -ne 0 ] ... - tests if file is open by some process</pre>
 === [[Short Notes on C/C++|C/C++]] ===
@@ Line 72: / Line 98: @@
 * How to clean up after child thread
 * Non-blocking IO using sockets
+* Shared Libraries on Linux+GCC
+* Singleton
+* <tt>std::move</tt> Semantics
+* Converting between <tt>std::string</tt> and <tt>std::wstring</tt> in C++11
+=== cURL (in terminal) ===
+Use '''-s''' option to make <tt>curl</tt> silent.
+* POST to server using cURL:
+<pre>curl --data "key1=value1&key2=value2" http://www.example.com/post.php</pre>
+* Upload to FTP server (with credentials), having connection timeout 60 seconds, and 120 seconds maximum operation time:
+<pre>curl --connect-timeout 60 -m 120 -T file.ext "ftp://12.34.56.78/folder" --user user:pass</pre>
+* Download from FTP server (with credentials):
+<pre>curl --user user:pass "ftp://12.34.56.78/folder/file.ext" -o ~/Downloads/file.ext</pre>
+=== [[Small Docker Notes|Docker]] ===
+=== [[Small elasticsearch Notes|ElasticSearch]] ===
+* Installation
+* What You Get
+* Indexing, Routing, etc.
+* Deleting
+* Getting and Multi-Getting
+* Updating
+* Search and Query DSL
 === [[Short Notes on ffmpeg|ffmpeg]] ===
+* ''process all files, may include spaces in file name:''
+ ls *.avi | while read f; do ffmpeg -i "$f" ''...params...'' "$f.mkv"; done
+* ''if you're having problems with input format, passing video through mpeg typically helps:''
+ ffmpeg -i file.mkv -qscale 2 -f mpeg - | ffmpeg -i - ''...params...'' file.avi
+* ''downmix 5.1 dolby to normal stereo:''
+ ffmpeg -i file.mkv ''...params...'' -acodec libmp3lame -ar 44100 -ac 2 file.avi
+* ''add an overlay image to the video:''
+ ffmpeg -i input.mp4 -i image.png -filter_complex "[0:v][1:v] overlay=''x'':''y'':enable='between(t,0,20)'" -pix_fmt yuv420p -c:a copy output.mp4
+This will add ''image.png'' as an overlay at position ''x'', ''y'' over the ''imput.mp4'' video, for the first 20 seconds.
+* ''fade in and out, first and last 25 frames of a 1000 frame video''
+ ffmpeg -i input.mp4 -vf "fade=in:0:25,fade=out:975:25" -acodec copy out.mp4
+* ''convert album contained in APE or similar file with CUE into separate MP3 tracks''
+ ffmpeg -i cd.ape -ab 256k cd.mp3
+ mp3splt -a -c cd.cue cd.mp3
+==== [[Short Notes on ffmpeg|more on ffmpeg]] ====
 * Rip DVD into FLV (or anything else)
+* Video File with Still Image and Audio
+* Concatenate Videos
+=== [[Short Notes on Flask and Flask-RestPlus|Flask and Flask-RestPlus]] ===
+=== [[Short Notes on git|git]] ===
+=== [[Short Notes on JS|All things JS - React, Vue, ...]] ===
+=== [[Small Kyoto Cabinet and Kyoto Tycoon Notes|Kyoto Cabinet and Kyoto Tycoon]] ===
+* Setup and Install Kyoto Cabinet
+* Setup and Install Kyoto Tycoon
+* KT's RPC API Reference
 === [[Short Notes on Linux Administration|Linux Administration]] ===
@@ Line 83: / Line 167: @@
 * Installing <tt>sendmail</tt>
 * Sending Emails using <tt>sendmail</tt>
+* Find and Mark Bad Blocks
+* Using TLP to optimize battery lifetime
+=== [[Short Notes on MAC OSX|MAC OSX]] ===
+* Asynchronous Execution
+** ''NSThread''
+** ''performSelectorInBackground''
+** ''dispatch_async''
+* ''MacPorts''
+ $ sudo port selfupdate
+ $ sudo port upgrade outdated
+ $ sudo port uninstall inactive
+ $ (just once) sudo port install port_cutleaves
+ $ sudo port_cutleaves
+=== [[Small MongoDB Notes|MongoDB]] ===
+* Installation on Ubuntu
+* Troubleshooting on Desktop
+* Use in PHP via PECL driver
+=== [[Short Notes on MySQL|MySQL]] ===
+* Error 1045: Access denied
+* The <tt>insert ... on duplicate key update</tt> Pitfall
+* Shrink ''ibfile1'' InnoDB File
+* Index JSON columns
 === [[Short Notes on PDF|PDF]] ===
@@ Line 94: / Line 206: @@
 * Convert Accented Characters to Non-Accented
 * Upload a File using cURL
+* HTTP Post in Pure PHP (without cURL)
+* Prevent Client Disconnect from Killing PHP
+* Disconnect Client and Continue Processing
+=== [[Short Notes on PSQL|PSQL, Postgres, PostgreSQL]] ===
+* Dump and Restore
+* Delete Duplicate Rows
+* Set Sequence Value to Max of Table's ID
 === [[Short Notes on Python|Python]] ===
 * Timing, and memory, on Linux
+* Importing Files
+* uWSGI, nginx, Flask
+* Decorators
+* virtualenv
+* SQLAlchemy
+* iPython fails with ''NameError: name 'sys' is not defined'' on autocompletion
+=== [[RedBeanPHP Cheat Sheet]] ===
+=== [[Short Notes on RESTful APIs|RESTful APIs]] ===
 === [[Short Notes on Security|Security]] ===
 * Password Generators
+* SSH Access using pubkey's Authentication
+* Using RSync together with SSH
+=== [[Short Notes on SVN|Subversion/SVN]] ===
+* Simple Guide to SVN Client
+* Creating a SVN Repository
+* Moving a SVN Repository
+* Change Repository URL (Subversion 1.7+)
+* Setup a SVN Server on a Shared Hosting with no ''root'' Access
+* creating and applying patch (the <tt>--diff-cmd</tt> is necessary in case you set some graphical diff-viewer in <tt>~/.subversion/config</tt>):
+<pre>cd root_of_project
+svn di --diff-cmd diff > ~/patch.diff
+cd root_of_other_project
+patch -p0 -i ~/patch.diff</pre>
+* ''svn:externals'' - pull ''repo1'' into ''dir1'', and ''repo2'' into ''dir2'':
+<pre>echo -e 'dir1 svn://repo1\ndir2 svn://repo2' > repos.txt
+svn propset svn:externals . -F repos.txt</pre>
+validate with " ''svn propget svn:externals .'' " .
+=== Ubuntu / Debian / Gnome etc. ===
+* restrict gnome app switcher to current workspace only:
+<pre>gsettings set org.gnome.shell.app-switcher current-workspace-only true</pre>
+* restore or undelete (config) file or directory:
+<pre># 1. check what package file or folder belongs to
+$ dpkg -S /path/my.conf
+# 2.a replace the config file; if it exists, will offer diff
+$ sudo apt-get -o Dpkg::Options::="--force-confask" install --reinstall <package-name>
+# 2.b restore the directory
+$ sudo apt-get -o Dpkg::Options::="--force-confask" install --reinstall $(dpkg -S /etc/some/directory | sed 's/,//g; s/:.*//')</pre>
+* increase number of inotify watchers
+<pre>$ cat /proc/sys/fs/inotify/max_user_watches
+$ echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf
+$ sudo sysctl -p
+$ cat /proc/sys/fs/inotify/max_user_watches
+</pre>
+==== Up-to-Date Versions of Packages ====
+* '''Python'''
+Ubuntu 18.04 ships with Python 3.6, but Amazon Linux uses 3.7, so e.g. to use and build Lambda layers and match those against packages you deploy, you need to install 3.7:
+<pre>$ sudo add-apt-repository ppa:deadsnakes/ppa
+$ sudo apt update
+$ sudo apt install python3.7 python3.7-venv</pre>
+Since these do not override default <tt>python</tt> and <tt>python3</tt> links (and better not!), you should create corresponding venv's as:
+<pre>$ python3.7 -m venv [env-dir]</pre>
+* '''NPM, node.js, etc.'''
+The default <tt>apt</tt> ''npm'' version is awfully outdated.
+'''update''' - available as a ''snap'' as well, no need to add ''apt'' sources - https://node.dev/node-binary
+Add NodeSource APT repo; for other versions, e.g. 12.x, change to <tt>setup_12.x</tt>.
+<pre>$ curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
+$ sudo apt update
+$ sudo apt install nodejs</pre>
 === [[Short Notes on ViM|ViM]] ===
@@ Line 108: / Line 297: @@
 * Directly type HTML entities
 * Reformat a plain text paragraph
-<pre>$ vim -x filename                   - open filename for editing, and save it encrypted (will prompt for a key)
+<pre>$ vim -x filename                      - open filename for editing, and save it encrypted (will prompt for a key)
-:X                                  - set encryption for current file; use ':set key=' to disable encryption
+:X                                     - set encryption for current file; use ':set key=' to disable encryption
-                                    - put "set cm=blowfish" in your .vimrc to enable safer encryption by default</pre>
+                                       - put "set cm=blowfish" in your .vimrc to enable safer encryption by default
+$ vim +10 [file] ; vim +/hello [file]  - open [file] at line 10, or at first occurrence of pattern 'hello' in file
+:w !sudo tee %                         - save file via `sudo` (as root)</pre>
+=== [[Short Notes on Wavelets|Wavelets]] ===
+* Integer Haar Wavelets in Python
 === [[Short Notes on Web|Web - HTML, CSS, JS, jQuery, etc.]] ===
@@ Line 125: / Line 320: @@
 ==== [[Install Apache and PHP to do Secure h264 Pseudo Streaming]] ====
+==== HTTP Response Codes ====
+This is not a definitive list, it's just stuff I use the most, and always forget which is which.
+* '''100''' - ''Continue''
+* '''200''' - ''OK''
+* '''201''' - ''Created''
+* '''202''' - ''Accepted''
+* '''204''' - ''No Content''
+* '''301''' - ''Moved Permanently''
+* '''302''' - ''Found'' (I typically use this instead of the '''307''' "''Temporary Redirect''")
+* '''304''' - ''Not Modified''
+* '''400''' - ''Bad Request''
+* '''401''' - ''Unauthorized''
+* '''403''' - ''Forbidden''
+* '''404''' - ''Not Found''
+* '''405''' - ''Method Not Allowed'' (using GET on POST calls, etc. - must include "Allow" response header)
+* '''406''' - ''Not Acceptable'' (mismatch of response format and "Accept" headers)
+* '''500''' - ''Internal Server Error''
+* '''501''' - ''Not Implemented''
+* '''503''' - ''Service Unavailable''