• File and Directory Permission

    File and Directory:

    ‘ll’ is used to display the information about the files and directory including date, time, users,group, size, name and permission.

    Four symbols are used when displaying permission.

    R : Read

    W : Write

    X : Execute

    - : no permission

    -rwxrwxrwx : files

    drwxrwxrwx : directory

    files and directory permission are symbolized by ten character.

    If we want to change permission, then there are two methods:

    1. symbolic
    2. Numeric

    1. Symbolic Method:

    Syntax:

    Chmod mode directory/filename

    Mode Option:

    1. u,g,o
    2. w,r,x
    3. +,-
    4. =

    1. # chmod u+rwx file or directory : in case of user only
    2. # chmod ug+rwx file or directoty : in case of user and group
    3. # chmod u+w,g+r,o+x directory/file
    4. # chmod u+rw,g+rw directory/file
    5. # chmod u-r, g-w,o-rw directory/file
    6. # chmod ugo+rwx file/directory
    7. # chmod ugo-rwx file/directory

    • + is used to add permission
    • - is used remove permission

    chmod ugo=rw directory/file

    this command will assign read/write permission to u,g,o

    suppose we have one file as

    test.txt

    permission : -r- - r- -r- -

    chmod u=w,g=wx,o=w test.txt

    this command will assign write to user, write/execute to group and write to other while remove the previous permission.

    The main difference between +,= are + operator simply add the new permission with previous one and = assign the new permission while removing old (new permission overwrite an old)

    1. Numeric Method:

    In this method, calculation are based on following numbers

    r=4 w=2 x=1 0= no permission

    Example:

    #chmod 777 file/directory

    in this case user get 7 means that user has permission of read/write/execute, group get 7 means read/write/execute and ame for other

    # chmod 531 file/directory

    in this case user get 5 means that user has permission of read/execute, group get 3 means write/execute and other get 1 means that other has permission to execute.

    #chmod 742 file/directory

    7 : User : rwx

    4 :Group : r

    2 : Other : w

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