====== Miscellaneous about computing ======
===== TCP ports repartitions =====

  * Well-known ports (0 to 1023),
  * registered ports (1024 to 49151),
  * dynamic, private or ephemeral ports (49152 to 65535).

The //Epeios// related software uses ports 53700 to 53799.

  * //xdhqxdh//, for both incoming (//FaaS//) connections **from** the //Atlas// toolkit, and outgoing connections **to** to the //Atlas// toolkit: ''53700'', 
  * //xdhwebq//: (incoming, from ''xdhq.php'' script): ''53710'',



===== Sharing 'Linux' folder to 'Windows' =====

http://www.howtogeek.com/176471/how-to-share-files-between-windows-and-linux/

==== Under 'Linux' ====


  * Install //samba//,
  * ''smbpasswd -a <username>'' (''<username>'' seems to need to be an existing login, despite what can be found in some documentation),
  * add following section in ''/etc/samba/smb.conf'' :
<code>
[<name>]
path = /home/<user_name>/<folder>
available = yes
valid users = <username>
read only = no
browsable = yes
public = yes
writable = yes
</code>
  * relaunch //samba// (''service smbd restart'').

==== Under 'Windows' ====

In the file explorer, type ''\\<host>\<name>'' (''<name>'' is the same name as the one given in the above section.

===== 'ssh' on same server but different OSes =====

When you try to connect with //ssh// on a machine with more then one OS (a tablet which can be boot under //Windows// or //Android//, for example), //ssh// will complain, or even forbid the connection when you switch the target machine from one OS to another.

One solution is to share the same key between both OSes.

The other solution is to connect to one OS, then comment out the concerned line in the ''known_hosts'' file, the connect to the other OS, and finally uncomment the previously commented line in ''known_hosts''. You can no connect to the 2 OS and //ssh// will no more complain.

===== nmap =====

<markdown>
- To scan local network : `nmap -sP 192.168.0.1/24`;
- `ip a` to obtain the IP to provide as parameter;
- `nmap -PS <IP>[/24]` to retrieve the opened ports.
</markdown>

===== Dimensions of a SVG element=====

Function returning an array containing the x and y coordinate of the top left corner, the width and the height of the drawing area of a SVG of id ''id''. 

<code javascript>
function svgViewBox( id ) {
 let x = 0;
 let y = 0;
 let width = 0;
 let height = 0;
 let svg = document.getElementById(id);
 let viewBox = svg.viewBox.baseVal;

 if ( viewBox !== null ) {
  x = viewBox.x;
  y = viewBox.y;
  width = viewBox.width;
  height = viewBox.height;
}

 if ( height === 0 ) {
  if ( width !== 0 )
   return "";
 } else if ( width === 0 ) 
  return ""

 if ( width === 0 ) {
  x = 0;
  y = 0;
  width = svg.width.baseVal.value;         
  height = svg.height.baseVal.value;         
 }

  return [x.toString(), y.toString(), width.toString(), height.toString()];
}

</code>

===== 'restic' =====

//restic// is a backup software.

To refer to a repository, use ''-r <repository>'', or the ''RESTIC_REPOSITORY'' environment variable (''RESTIC_REPOSITORY=<repo>''). Example: ''RESTIC_REPOSITORY=sftp:user@server:restic-repo restic …''.

By default, //restic// will ask for the password. Using the ''RESTIC_PASSWORD''  environment variable to avoid this. Example ''RESTIC_PASSWORD=mypasswd restic …''.

A //restic// repository can be accessed through a mountpoint under //Linux// (should also work under //Windows// with //WSL//) : ''restic -r <repo> mount <mountpoint>''. The different snapshots are the located in ''<mountpoint>/snapshots''.

===== 'Kate' =====
<markdown>
*[Kate](https://en.wikipedia.org/wiki/Kate_(text_editor))* sometimes adds a new line at the end of a file, even if the file contents only one line. For example, type the `a` letter and save the file; the file will have a size of 2 bytes.  
This behavior can be changed by unchecking *Settings* / *Configuring Kate…* / *Editor Component* / *Open/Save* / *Automatic Cleanups on Save* / *Append newline at end of file on save*.
</markdown>

===== Attaching a process to the debugger does not work (Linux) =====

https://stackoverflow.com/questions/19215177/how-to-solve-ptrace-operation-not-permitted-when-trying-to-attach-gdb-to-a-pro

''echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope'' or ''sudo bash -c "echo 0 > /proc/sys/kernel/yama/ptrace_scope''.

===== Monitoring SSL/TLS certificate =====

To prevent a MITM attack on a SSL/TLS protected connexion (https://linuxfr.org/users/samuel/journaux/predator-files-surveillez-les-logs-certificate-transparency-sur-vos-domaines (fr)), certificate logs can be monitored through https://crt.sh/. Example: https://crt.sh/?q=linuxfr.org&deduplicate=Y.

Monitoring can be done through an ATOM feed. Example: https://crt.sh/atom?q=linuxfr.org&deduplicate=Y.