Linux File system permissions (ii)

Special permissions

Effects of special permissions on files:

U+w (SUID) executes the file as the user who owns the file, not as the user who runs the file

G+s (Sgid) executes the file as a group that owns the file

O+t (sticky) no impact

Impact on the directory:

U+w (suid) No impact

G+s (Sgid) The newly created file in the directory sets its group owner to match the group owner of the Directory

O+t (sticky) users who have write access to the directory can only delete all of their files, but cannot delete or force them to files owned by other users

Example:

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Default File Permissions

The default permissions for files are set by the process that created them.

These permissions are typically not set when new files and directories are created, some of which are purged by the umask of the shell process.

Running the umask command without parameters will display the current value of the Shell's Umask

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Each process of the system has umask, which is an octal bitmask that clears the permissions for new files and directories created by the process. If a bit is set in Umask, the corresponding permissions in the new file are cleared. Umask clears all groups and other permissions for the newly created file at 077.

Directory permissions: 777 Umask: (0) 022

111 111 111

010 010 = 111 101 101 = 755 (rwx r-x r-x)

File permissions: 666 Umask: (0) 022

110 110 110

010 010 = 644 (rw-r--r--)

Normal User: 775 Umask: (0) 002

111 111 111

010 = 111 111 101 = 775 (rwx rwx r-x)

Privileged Users: 755 Umask: (0) 022

111 111 111

010 010 = 111 101 101 = 755 (rwx r-x r-x)

Note: It is not possible to subtract from the calculation, it should be compared to the corresponding location is 1, the position of 1 becomes 0, in other cases, the value of the position is unchanged.

This article is from the Linux Learning Notes blog, so be sure to keep this source http://10516823.blog.51cto.com/10506823/1721338

Linux File system permissions (ii)