How to decode 6 digits file mode on AIX?

Question

The file mode for a file on AIX returned by the Ruby stat method has 6 digits:

ruby -e 'puts File::stat("testfile_upload-003").mode.to_s(8)'
100644

FWIW, Ruby version is ruby 2.1.6p336 (2015-04-13 revision 50298) [powerpc-aix6.1.0.0], but Perl returns the very same value:

perl -e 'use File::stat; printf "%o\n", stat("testfile_upload-003")->mode;'
100644

Here is the output of istat for the same file.

# /bin/istat testfile_upload-003
Inode 33780 on device 10/7      File
Protection: rw-r--r--
Owner: 0(root)          Group: 0(system)
Link count:   2         Length 51200 bytes

Last updated:   Thu Mar  9 01:13:24 CST 2017
Last modified:  Wed Mar  8 11:52:52 CST 2017
Last accessed:  Wed Mar  8 11:52:52 CST 2017

EDIT: the chmod man page andistat man page do not provide info for the 5th and 6th digits.

And there is no fancy setuid bits set for that file:

# ls -l testfile_upload-003
-rw-r--r--    2 root     system        51200 Mar 08 11:52 testfile_upload-003

@roaima i forgot to mention I RTFMed and did not find info beyond the 4th digit. — philant, Mar 09 '17 at 08:39

score 3 · Answer 1 · answered Mar 09 '17 at 08:58

3

I found them in <sys/mode.h> :

/*
 *      (stat) st_mode bit values
 */

#define _S_IFMT         0170000         /* type of file */
#define   _S_IFREG      0100000         /*   regular */
#define   _S_IFDIR      0040000         /*   directory */
#define   _S_IFBLK      0060000         /*   block special */
#define   _S_IFCHR      0020000         /*   character special */
#define   _S_IFIFO      0010000         /*   fifo */

The leading '1' indicates a regular file.

A directory has 240755, the '4' indicates a directory, and the '2' means "not a regular file".

answered Mar 09 '17 at 08:58

philant

201

That's it. You can read up on the stat() function in POSIX to get the details. – Stephen Kitt Mar 09 '17 at 09:01
2

And of course Perl has the equivalent test macros and Ruby seems to have similar tests too. Since the lower bits are specified in the standard, you can just mask with 0777 to get the usual permission bits. – ilkkachu Mar 09 '17 at 10:16

score 2 · Answer 2 · edited Jul 16 '20 at 23:10

The *NIX systems (an AIX is a UNIX, but it's true on Linux, Solaris and BSD too) has 16bit long file mode info: 4bit for file type; 3bit for special bits (setuid, setgid, t-git or sticky); and 9bit for permissions (owner rwx, group rwx, others rwx - rwx means read-write-execute). The standard enables the octal representation (without leading zeros - which are sometimes writen), first one or two is the file type, next one is for the special bits, last three is for permissions.

Examples (3 binary digit = 1 octal digit):

Binary 1000000111101101 = Octal 100755 (-rwxr-xr-x)
Binary 0100000110100100 = Octal 40644  (drw-r--r--)
Binary 1010000111111111 = Octal 120777 (lrwxrwxrwx)
The previous examples in parts:
Binary 1/000 000 111/101/101 = Octal 10 0 755 = -rwxr-xr-x
Binary 0/100 000 110/100/100 = Octal 4 0 644  = drw-r--r--
Binary 1/010 000 111/111/111 = Octal 12 0 777 = lrwxrwxrwx

The file types:

10 (-) = regular file
4 (d) = directory
12 (l) = symbolic link
1 (p) = FIFO (named pipe)
14 (s) = socket
2 (c) = character special file (like TTY, eg.: /dev/tty1)
6 (b) = block special file (like HDD, eg.: /dev/sda)
and in other systems there are more (eg. Solaris D = door, P = port; etc.)

Special bits value in the octal number (4th from right): setuid = 4, setgid = 2, sticky = 1. — kgyt, Jul 16 '20 at 22:28
You are encouraged to edit your post if you want to include additional relevant information. — AdminBee, Jul 17 '20 at 07:31

How to decode 6 digits file mode on AIX?

2 Answers2

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