Linux File Types and File Modes
More info on inode manpage
File type and permission are stored as a 16-bit “value”
Higher 4-bits: for storing file type (max 16 file type possible)
Lower 12-bits: for storing permissions : for special, user, group, other : each can have 7 combinations of read-write-execute + 1 for no permission
The “value” is typically represented in octal notation.
e.g. A regular file with rwxr—r— permission will have value “0100744”, where
0 - no idea why its there
10 - regular file
0744 - file permissions
File types
Each file can have only 1 file type
( ‘x’ in the value column corresponds to file mode )
| Value (octal) | Notes |
|---|---|
| 014xxxx | socket |
| 012xxxx | symbolic link |
| 010xxxx | regular file |
| 006xxxx | block device |
| 004xxxx | directory |
| 002xxxx | character device |
| 001xxxx | FIFO |
File modes
Special permissions (set UID, set GID, sticky) have higher priority over other permissions
You can combine the permissions by adding the values
e.g. 4754: set UID enabled, u=rwx, g=rx, o=r
( ‘x’ in the value column corresponds to file mode )
| Value (octal) | Notes |
|---|---|
| 0xx4000 | set UID bit |
| 0xx2000 | set-group-ID bit (see below) |
| 0xx1000 | sticky bit (see below) |
| 0xx0400 | owner has read permission |
| 0xx0200 | owner has write permission |
| 0xx0100 | owner has execute permission |
| 0xx0040 | group has read permission |
| 0xx0020 | group has write permission |
| 0xx0010 | group has execute permission |
| 0xx0004 | others have read permission |
| 0xx0002 | others have write permission |
| 0xx0001 | others have execute permission |