chmod 2755 work/

**vickey_20** · 06-21-2009

I came across this command on the red hat site

Code:

chmod 2775 /usr/share/emacs/site-lisp

the link is here 32.5.1.*Group Directories
I find it confusing , how come there are 4 number specifying the permission and also doing as instructed the permission of the directory has a 's' in the groups place . What does this mean???

**RFahy** · 06-21-2009

The "s" would stand for "sticky" I believe. For directories where anybody can add files, yet nobody can delete them.

Edit: my mistake, above. You have set the Set Group bit.
From what I know, that means that the file/folder will borrow the owner user's group ID.
Same for Set User bit which borrows owner user's user ID.
Here's the manpage, please do correct me if I said anything wrong.

man chmod:

Code:

      A numeric mode is from one to four octal digits (0-7), derived by adding
       up  the  bits with values 4, 2, and 1.  Omitted digits are assumed to be
       leading zeros.  The first digit selects the set  user  ID  (4)  and  set
       group ID (2) and restricted deletion or sticky (1) attributes.

**vickey_20** · 06-22-2009

there are supposed to be only three digits for assigning permission If I m not wrong . So wat is that extra '2' doing there?

**meton_magis** · 06-22-2009

as previously stated, the 2 adds the group's sticky bit. any file created in that directory after that bit is set will automaticaly inherit the group owner.

most commands in linux have several syntaxes to be able to do different things. by putting 4 numbers instead of 3, you modify the sticky bit settings.

**RFahy** · 06-22-2009

Originally Posted by vickey_20

there are supposed to be only three digits for assigning permission If I m not wrong . So wat is that extra '2' doing there?

Actually there are supposed to be 4 digits. But since few really need to mess with the SGUID, SUID and Sticky bits, only the basic 3 are used for permissions. The missing digits are considered zero.

So if I were to use

Code:

chmod 7 file.txt

, it would be the same as using

Code:

chmod 0007 file.txt

**vickey_20** · 06-22-2009

Originally Posted by RFahy

Code:

chmod 7 file.txt

, it would be the same as using

Code:

chmod 0007 file.txt

shouldn't be it this way

Code:

permission for new file 
0700 file.txt

**RFahy** · 06-22-2009

You're invited to try it out and see for yourself.

Code:

chmod 7 file.txt
ls -l file.txt

**vickey_20** · 06-22-2009

ya you are right !!

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