[ILUG] umask query

[Brian Foster]

  | Date: Fri, 22 Apr 2005 19:11:52 +0100
  | From: Sean O Sullivan <seanos at netsoc.itcarlow.ie>
  | 
  | Need files and directories to be created with permissions '775'.
  | umask should then be set to '002', however, apparently when set umask
  | it is set, it will dictate that directories will be created as '775',
  | however files as '644' (with a umask of 002).

 that is not quite correct.  or at least it appears you
 may believe the umask can do something that it cannot
 actually do, and was not designed to do.

 the umask(2) _clears_ (sets to 0) unwanted permissions
 bits _specified_ by the creating open(2) (for files)
 or mkdir(2) (for directories).  so, if yer file is
 being created by:

    open("file", O_CREAT|..., 0666)

 as is usually the case --- 0666 is almost always the
 mode specified (for files, 0777 for directories) ---
 it is absolutely _impossible_ for the umask to cause
 any of the eXecute bits (0111) to be set (for files).
 the umask can cause any of the specified 0666 bits to
 be cleared.  e.g., for yer example umask of 002, that
 bit would be cleared resulting in 0664 (rw-rw-r--),
 as you have observed.

  | This is a problem, as I need both to be 775...
  | Is there any solution for this ?

 either chmod(2)/fchmod(2) the file after creation,
 or change the permissions specified in the creating
 open(2).  I suggest fchmod since that will make you
 independent of the umask, which it seems is what
 you are really after.  either solution does imply
 modifying the source code.

cheers!
	-blf-
-- 
Experienced (20+ yrs) kernel/software Eng: | Brian Foster   Montpellier,
 • Unix, embedded, &tc;  • Linux;  • doc;  | blf at utvinternet.ie   FRANCE
 • IDL, automated testing, process, &tc.   |  Stop E$$o (ExxonMobile)!
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