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===== Cluster access =====
Access to the cluster is made trough an independent virtual machine called ''frontend''(''ctcomp2.inv.usc.es''). This ''frontend'' has very limited resources and it's only purpose is to manage file transfers and job submissions to queues. __Code execution is not allowed in this server__. 

Remote access to the ''frontend'' is made with ''ssh'' (//secure shell//). Access credentials are the CITIUS ones.  //Note: If having problems connecting using the hostname then use the IP address instead: ''172.16.242.122''.//

<code bash>
local$ ssh [-X] -p 1301  citius_user@ctcomp2.inv.usc.es
Password:
ctcomp2$ 
</code>
The ''-X'' parameter is optional. Connects the X redirection. It is an essential requirement in order to execute programs that need a graphical mode.


===== File import/export =====

The cluster's filesystems are independent and are isolated from the CITIUS network so it is necessary to import to the cluster's user space all necessary files to execute our programs (for example, source code or the input files).

An user has the following places available, inside the cluster's filesystem, to place his files:


  *  ''/home/local/name.surname/''\\  This directory is the user's ''$HOME'' and is accessible from all the cluster nodes including the ''frontend''. By default it is the reference directory of code accessed by all running jobs in the computing nodes. Each user's available space is limited by quotes, so very big files will have to be stored in the ''/sfs/'' directory. 
<note warning> **NO backups are made of the user's ''$HOME'' directory.**</note>

  *  ''/sfs/''\\ This directory is also shared between the nodes and the ''frontend''. It can be used as an auxiliary space during job execution, for temporary file files that need to be accessible by all nodes or to store files resulting from job execution.  Inside this directory ** any file not accessed in the last 30 days can be deleted**. It is recommended to use file/directory names that identify clearly the coupling between user and programs to avoid potential conflicts between users.

  *  ''/scratch/'' \\ Each node has a local //scratch// directory that can be used for temporal local storage during job execution. The contents of the //scratch// directory is not visible from other nodes nor is visible from the ''frontend'', as such is not a good choice for storing results files. **The content of this directory can be erased any time**. It is recommended to use file/directory names that identify clearly the coupling between user and programs to avoid potential conflicts between users. 
 

To import and export the necessary files in and out the cluster the ''scp'' command is used. It allows the user to move files between other file systems in the network. Syntax of the ''scp'' command is the following:
<code bash>
scp -P 1301 [-r] <source_address> <destination_address>
</code>
Argument explanation:
  * ''-r'' (//optional//) Used whenever ''source address'' is a directory and denotes that directory contents must be copied recursively. 
  * ''<direccion_origen>'' Indica la ruta completa del fichero/directorio que se copiará.
  * ''<direccion_destino>'' Indica la ruta completa donde queremos ubicar la copia del fichero/directorio.

=== scp command examples in ctcomp2 ===

As an example, several cases of file imports are shown. In this examples it is assumed that the user is ''user.name'' and that his workplace is ''ctXXX.inv.usc.es''. The file/directory to be imported is located in ''ctXXX.inv.usc.es'' in the ''/datos/work/'' directory and that we want to copy them to the user's working space in the cluster in the directory ''work'' in the user's ''$HOME''. 
If we use ''scp'' from inside the cluster after logging in trough ssh:

<code bash>
ct$ scp -P 1301  user.name@ctXXX.inv.usc.es:/datos/work/one.file  ~/work/
ct$ scp -P 1301  -r user.name@ctXXX.inv.usc.es:/datos/work/directory/  ~/work/
</code>

Id using ''scp'' from our own computer:
<code bash>
local$ scp -P 1301 /datos/work/one.file  user.name@ctcomp2.inv.usc.es:~/work/
local$ scp -P 1301  -r /datos/work/directory/   user.name@ctcomp2.inv.usc.es:~/work/
</code>