Special permission on file folder

SPECIAL PERMISSION ON FILE AND FOLDER:

What is special file permission?

Three special types of permissions are available for executable files and public directories. When these permissions are set, any user who runs that executable file assumes the user ID of the owner (or group) of the executable file. Thats are following:

                                                                                              I.        SUID  (setuid)

                                                                                             II.        SGID   (setgid)

                                                                                             III.        Sticky Bit

With the help of “chmod”command  we can implement the special permissions on file and directories.

SUID:

What is SUID (Set Owner User ID)?

When set-user identification (setuid) permission is set on an executable file, it is executed with the file owner’s permissions (rather than with the permissions of the user who executes it).

For example, the setuid permission on the passwd command makes it possible for a user to change passwords, assuming the permissions of the root ID:

-r-sr-sr-w   3 root     sys       107680 dec 18 01:02 /usr/bin/passwd

Use chmod command to set SUID on anshuman.txt:

                    #chmod u+s anshuman.txt

How can I check if a file is set with SUID?

                    #ls -l
                    total 8
                    -rwsr–r– 1 sara  mary  148 Dec 18 03:46 anshuman.txt

How can I find all the SUID set files in Linux?

                # find / -perm +4000

SGID:

What is SGID (Set Group ID)?

SGID is similar to SUID. The difference between both is that SUID assumes owner of the file permissions and SGID assumes group’s permissions when executing a file instead of logged in user inherit permissions.

Use chmod command to set SGID on anshuman.txt:

                    #chmod g+s anshuman.txt

How can I check if a file is set with SGID?

              #ls –l

              total 8

              -rwxr-sr-- 1 sara marry  148 Dec 18 03:46 anshuman.txt

How can I find all the SGID set files in Linux?

               #find / -perm +2000

STICKY BIT:

What Is Sticky bit?

Sticky Bit is mainly used on folders in order to avoid deletion of a folder and its content by other users though they having write permissions on the folder contents. if the directory has the sticky bit set, a file can be deleted only by the owner of the file, the owner of the directory, or by root. 

Use chmod command to set Sticky bit on a folder named /secret:

                     #chmod +t /secret

How to check a folder is set with Sticky Bit?

                    #ls -l

                    total 8

                    -rwxr-xrwt 1 sara marry 148 Dec 18 03:46  /secret

How can I find all the Sticky Bit set files in Linux?

                     #find / -perm +1000