File Permissions and Umask

 permissions:-

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-> the set of rules set according to users & groups & others are called as permissions

-> we 3 basic permissions

-> in the permission "." after the permissions is represents that mo ACL permission is applied.

1) read --> r --> 4

2) write -> w --> 2

3) execute -> x -> 1

#ls -l  --> to list the perm of all normal files & dir

user owner group owner others

- rw- r-- r-- <user owner> <group owner> ----- ---- <filename>

d rwx r-x r-x <user owner> <group owner> ----- ----- <dir name>

- rw-rw-rw-

d rwxrwxrwx 

umask [user mask]

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-> umask value determines default permissions on file & dir

-> max perm for file is 666

-> max perm for dir is 777

-> by default umask vaule of root user  "022"

-> by default umask vaule of normal user "002"

-> umask is nothing but changing the perm of file or dir before creation

-> to know the umask value of perticular user is

#umask  

022

$umask 

002

file:

*****

max perm for normal file 666 (rw-rw-rw-)

default umask vaule of root user 022 (    w  w )

  (-)

************************************************************

default perm for  file is 644     (rw-r--r--)

************************************************************

dir:-

****

max perm for normal dir 777 (rwxrwxrwx)

default umask value of normal user 002 (       w )

   (-)

**************************************************************

default perm for dir is 775 (rwxrwxr-x)

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changing the umask value:-

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1) temperary 

2) permanent

temperary:-

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#umask   --> to know the present umask value

#umask <umask vaule>   --> to change the umask value temp

ex: #umask 000       --> it will not remove any perm

#umask

#touch g1 

# ls -l g1

-rw-rw-rw-  --- ----- ------ g1

permanent:-

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-> edit config file /etc/bashrc

#vim /etc/bashrc

-> fot changing root user umask value go to line  77 line

-> for chnaging normal user umask value go to line 75 line

:wq!

#umask  --> the changes will not be done until u exec the shell

#exec bash  --> to update the shell with default settings

#umask