Folders:
- /sbin/ = Linux discriminates between 'normal' executables and those used for system maintenance and/or administrative tasks. The latter reside in '/sbin' 
   or - the less important ones - in '/usr/sbin'.  
- /usr/sbin/= System administrative programs.
- /usr/local/sbin/ = Locally installed system administration programs
- /etc/ = Contains system configuration files such as psswd, hosts, shodow, fstab

Files:
- ~/.bash_profile = User's personal configuration file for login shells. Here you write the PATH variable
 Ex: # User specific environment and startup programs
     PATH=$PATH:$HOME/bin
     PATH=$PATH:/usr/sbin:/sbin
     PS1="[\u@\w] > " 
- /etc/bashrc = global configuration file. 
 Ex: # System wide functions and aliases
     alias lls='ls -lh'
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- /etc/fstab = is a configuration file that contains information of all the partitions and storage devices in your computer. The first column contains the device name, 
 the second one its mount point, third its filesystem type, fourth the mount options, fifth (a number) dump options, and sixth (another number) filesystem check options.
 Link: ../netLinux/fstab.html
 Exemplu:
  /dev/hda1       /mnt/windows    ntfs    ro,defaults,umask=0222  0 0
  /dev/hda5       /mnt/vfat       vfat    uid=daniel,umask=017    0 0
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- /boot/vmliuz* =  where linux kernel is located
- /etc/passwd = This file holds the majority of information about accounts on the Unix system
- /etc/shells = is  a text file which contains the full pathnames of valid login shells

Environment Variables
- PS1 = controls the top-level command prompt, or string of characters before the cursur
- PATH = contains a list of directories where executables files might be located



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- PS1 = controls the top-level command prompt, or string of characters before the cursur

 Exemplu: PS1="[\u \w] > " 
Escape_Sequence = Function
\t = Current time, expressed as HH:MM:SS.
\d = Current date, expressed as Weekday Month Date (or Day).
\n = Newline.
\s = Current shell environment.
\W = Working directory.
\w = Full path of the working directory.
\u = Current username.
\h = Hostname of the current machine.
\# = Command number of the current command. Increases with each new command entered.
\$ = If the effective UID is 0 (that is, if you are logged in as root), end the prompt with the # character; otherwise, use the $.
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- PATH = contains a list of directories where executables files might be located
The value of the PATH variable is usually set in a configuration file such as '/etc/profile'. You can add your own values to the PATH variable.
 PATH=$PATH:new_value
 Exemple: PATH=$PATH:/usr/sbin/
Multiple directories can be added as a colon-separated list ('director1:director2'). The user can add the command 
 export PATH -> the new value of the variable will be available outside of that particular iteration of the shell
The $ sign at the beginning of the PATH statement tells the shell that the new directory is to be appended to the current value of PATH rather than
replacing it.