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Linux Unhatched (Basic Command Syntax (Pattern: command [options…]…

- - - - Multiple options can be used at once
        
        given as separate options as in -l -r
        
        or combined like -lr
- - - - The first argument is the source
      - The second argument is the destination
    - - Moving a file requires write and execute permissions on both the origin and destination directories.
  - - - execute permission to access the directory where the file is located and the read permission for the file being copied
      - is also necessary to have write and execute permission on the directory the file is being copied to
    - - is a utility for copying files or entire partitions at the bit level
      - It can be used to clone or delete (wipe) entire disks or partitions.
      - It can be used to copy raw data to removable devices, such as USB drives and CDROMs.
      - It can backup and restore the MBR (Master Boot Record).
      - It can be used to create a file of a specific size that is filled with binary zeros, which can then be used as a swap file (virtual memory)
      - dd if=/dev/zero of=/tmp/swapex bs=1M count=50
        
        if
        Input File: The input file to be read from.
        
        of
        Output File: The output file to be written.
        
        Block Size: The block size to be used. By default, the value is considered to be in bytes. Use the following suffixes to specify other units: K, M, G, and T for kilobytes, megabytes, gigabytes and terabytes respectively.
        
        count
        Count: The number of blocks to be read from the input file.
      - No block size or count needs to be specified when copying over entire devices.
  - - - -r or -R recursive
    - - To delete a file within a directory, a user must have write and execute permission on a directory
      - Regular users typically only have this type of permission in their home directory and its subdirectories.
- - - - ls -r: reverse print the results in reverse alphabetical order
      - ls -l: long display, gives more information about each of the files listed
        
        Type of file
        
        The first field actually contains ten characters, where the first character indicates the type of file and the next nine specify permissions.
        
        d - directory - A file used to store other files.
        
        '-' regular file - Includes readable files, images files, binary files, and compressed files.
        
        'l' - symbolic link - Points to another file.
        
        's' - socket - Allows for communication between processes.
        
        'p' - pipe - Allows for communication between processes.
        
        'b' - block file - Used to communicate with hardware.
        
        'c' - character file - used to communicate with hardware
        
        Permissions
        
        Hard Link Count
        
        User Owner
        
        Group Owner
        
        File Size
        
        Timestamp
        
        Filename
      - ls -t: The -t option will sort the files by timestamp
      - By default the output of the ls command is sorted alphabetically by filename
      - ls -l -S: sort the files by file size
    - - move to the root directory
    - - always starts at the root directory - /
    - - Relative paths do not start with the / character, they start with the name of a directory
    - - parent directory
    - - current directory
    - - home directory
- - - - -rw-rw-r-- 1 sysadmin sysadmin 21 Aug 1 02:35 hello.sh
        
        '-' iniziale rappresenta il tipo di file
      - Permissions Field
        
        three sets of three characters
        
        first set
        
        The first set is for the user who owns the file
        
        second set
        
        The second set is for the group that owns the file.
        
        third set
        
        The last set is for everyone else, any one who that first two sets of permissions do not apply to
    - - read (r)
        
        Allows for file contents to be read or copied.
        
        Without execute permission on the directory, allows for a non-detailed listing of files. With execute permission, ls -l can provide a detailed listing.
      - write (w)
        
        Allows for contents to be modified or overwritten
        
        For this permission to work, the directory must also have execute permission.
      - execute (x)
        
        Allows for a file to be run as a process, although script files require read permission, as well.
        
        Allows a user to change to the directory if parent directories have write permission as well.
    - - The chmod command is used to change the permissions of a file or directory.
      - Only the root user or the user who owns the file is able to change the permissions of a file.
      - two techniques for changing permissions
        
        symbolic
        
        good for changing one set of permissions at a time
        
        only the symbolic method will be covered
        
        chmod [<SET><ACTION><PERMISSIONS>]... FILE
        
        SET
        
        u User: The user who owns the file
        
        g Group: The group who owns the file.
        
        o Others: Anyone other than the user owner or member of the group owner.
        
        a All: Refers to the user, group and others.
        
        ACTION
        
        + Add the permission, if necessary
        
        = Specify the exact permission
        
        - Remove the permission, if necessary
        
        PERMISSION
        
        r read
        
        w write
        
        x execute
        
        octal
        
        requires knowledge of the octal value of each of the permissions
        
        requires all three sets of permissions (user, group, other) to be specified every time
  - - - The first argument, [OWNER], specifies which user is to be the new owner
      - The second argument, FILE, specifies which file's ownership is changing
- - - - less
        
        Not covered
      - more
        
        Not covered
      - head
        
        head [OPTIONS] [FILE]
        
        The -n option can be used to specify the amount of lines to display
        
        head -n number_of_lines filename
      - tail
        
        tail [OPTIONS] [FILE]
        
        The -n option can be used to specify the amount of lines to display
  - - - The grep command is a text filter that will search input and return lines which contain a match to a given pattern.
      - grep [OPTIONS] PATTERN [FILE]
        
        Regular Expressions
        
        Basic
        
        '.' - Any one single character
        
        '[ ]' - Any one specified character
        
        [^ ] - Not the one specified character
        
        '*' - Zero or more of the previous character
        
        '^' - If first character in the pattern, then pattern must be at beginning of the line to match, otherwise just a literal
        
        '$' - If last character in the pattern, then pattern must be at the end of the line to match, otherwise just a literal $
        
        Extended
        
        egrep oppure grep -E
        
        '+' - One or more of the previous pattern
        
        '?' - The preceding pattern is optional
        
        { } - Specify minimum, maximum or exact matches of the previous pattern
        
        | - Alternation - a logical "or"
        
        ( ) - Used to create groups
- - - - Preventing regular users from executing these commands helps to protect the system
      - su OPTIONS USERNAME
      - It does this by creating a new shell
      - su - or su -l or su --login
      - command exit to logout
    - - sudo [OPTIONS] COMMAND
      - Allows a user to execute a command as another user without creating a new shell
      - sudo -u: switch to another user