Special Permissions in Linux . {setUID,setGID,Sticky Bit]

Special Permissions:
````````````````````
setUID
setGID
Sticky Bit

setUID: Is allocated for files, so that who ever may run this file, process owner will be the owner of file(script).
 chmod u+s hello.sh
 
 hello.sh--> rw-r--r-- ==> rwSr--r--

setGID:
 file: how ever my run the script, process group will be the scripts  actul group.

 dir: Who ever may create a file in this directory, the file group  will be same as of the directory group.

 ex: 
 # mkdir /king (owner:root, group: root)
 # chmod g+s /king [rwxrwsr-x]

 User kumar creates a file in this directory
 hello.txt --> owner: kumar, group: root


sticky bit:
Is set only on directory so that any user can create files in this directory, but only the owner of file can remove such file, but not others

# chmod o+t /stage [rwxrwxrwt]

user: kumar
$cat > /stage/madhu.txt
ds;lfjl;sjdgl;
ctrl+z

user: madhu
$rm /stage/madhu.txt --> error

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ACL: Access Control List
Using ACL we can give permissions to specific users/groups on a file/dir

setfacl -m : to add ACL permissions
 syn: setfacl -m <whome>:<name>:<permissions> filename

 ex: setfacl -m u:user1:rw hello.txt
     setfacl -m u:user2:r hello.txt
     setfacl -m g:dba:rwx hello.txt

setfacl -x: to remove permissions
 syn: setfacl -x <whome>:<name> filename

 ex: setfacl -x u:user1 hello.txt
     setfacl -x u:user2 hello.txt
     setfacl -x g:dba  hello.txt

getfacl: to view permissions on a file
 syn: getfacl filename
 ex: getfack hello.txt

note: for a newly created partition we have set acl,user_xattr mount options so that files in this partition can be set with ACL permissions
 tune2fs -o acl,user_xattr /dev/sda7