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Full Discussion: help on umask
Operating Systems Linux help on umask Post 302184418 by era on Friday 11th of April 2008 12:12:41 PM
Old 04-11-2008
You cannot change the permissions on already created files by changing the umask. It affects the permissions when the file is created, but after that, you need to use chmod to change permissions.

If you know your umask and the file mode passed in when a file is being created, you can figure out what permissions the file is going to have, but there is a simple boolean calculation involved, and if you don't want to perform that, you cannot magically know the answer.

If your umask is 000 then the file will have whatever permission the creating application requested (typically 666 or 644). If your umask is 077 then the file will have the "group" and "other" permission bits forced to zero, and your own permission set to whatever the application requested (typically 600). The number of possible combinations is quite small (and only a fraction of them are ever seen in practice) and the calculation is not at all hard to do in your head.
 

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LEARN ABOUT HPUX

umask

umask(2)							System Calls Manual							  umask(2)

NAME

       umask - set and get file creation mask

SYNOPSIS

DESCRIPTION

       sets  the  process's  file mode creation mask to cmask and returns the previous value of the mask.  Only the file access permission bits of
       the masks are used.

       The bits set in cmask specify which permission bits to turn off in the mode of the created file, and should be specified using the symbolic
       values defined in stat(5).

EXAMPLES

       The  following creates a file named in the current directory with permissions so that the file can be written only by its owner, and can be
       read or executed only by the owner or processes with group permission, even though group write permission and all  permissions  for  others
       are passed in to

RETURN VALUE

       The previous value of the file mode creation mask is returned.

SEE ALSO

       mkdir(1), sh(1), mknod(1M), chmod(2), creat(2), mknod(2), open(2).

STANDARDS CONFORMANCE

																	  umask(2)
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