POSIX File Permissions

Fourth Digit

Sticky Bit (1)

• Prevents users from deleting or renaming others users files contained within a directory.
• chmod +t DIRECTORY
• Other executable and Sticky Bit set: ——–t
• Sticky Bit set but not other executable: ——–T

SetUID Bit (2)

• Files are executed with the same permissions as the files owner.
• No effect on directories.
• chmod u+s FILE
• User executable and SUID set: –s——
• SUID set but not user executable: –S——

SetGID Bit (4)

• Files are executed with the same permissions as the files group.
• New files created in the directory inherit the directory’s group.
• chmod g+s FILE
• Group executable and SGID set: —–s—
• SGID set but not group executable: —–S—

Additional Symbols