Can anyone tell me what means the first 's' in the output of ls -l ?

ex:
#ls -l

srwxr-xr-x 1 root root 0 Apr 21 2004 linc-a94-0-4cbff69b36d2



thanks,
ddaas

it means it's suid bit is set. if you run that file (if it is executable) it will appear to be run by root, as root owns it, and not the person who is actually running it. this can be really handy in overcoming fundamental permissions issues

thanks

When I make: chmod 4777 file_name

then I type: ls -l

-rwsrwxrwx 1 user1 group1 15 Jan 20 16:12 file_name


The 's' bit is where 'x' bit shuld be. That's OK.


But why is for the other file 's' bit where '-' or 'd' should be?

srwxr-xr-x 1 root root 0 Apr 21 2004 linc-a94-0-4cbff69b36d2

I picked up a reference book to check on things, and here's what it said:

The first character in the output of "ls -l" is the file type.
"-" - regular file
"d" - directory
"c" - character device file
"b" - block device file
"s" - UNIX domain socket
"p" - named pipe
"l" - symbolic link

So it looks like the file is a communications socket.

The setuid, setgid, and sticky bits are indicated in positions 4, 7, and 10 respectively (counting from left - the same characters that indicate execute permissions). Setuid and setgid are represented by either a lowercase or capital "s", while the sticky bit is represented with a lowercase or capital "t". If none of the special bits are set, the permissions are displayed as "-" or "x" like normal. If one of them is set, then a capital letter is used if the same execute permission is not set. A lowercase letter is used if the corresponding execute permission is set.

Thanks a lot. Now is all clear for me.

I have 2 more questions:

1) What is that reference book?
2) What is a "Unix Domain socket"? I guess it has nothing to do with the socket from tcp/ip (ip+protocol+port).



Thanks again,
ddaas

The book is: "Linux Administration Handbook" by Evi Nemeth, Garth Snyder, and Trent R. Hein. It covers a lot of things in good detail, but its shortcoming is the index. There are some index entries that give incorrect page numbers for topics.

As far as I understand them, a file-based socket is an interface for one process to communicate with another process. For instance, I believe the MySQL database server creates a socket when it's started. Other processes can use that socket to query the database.