06-03-2005
Set GID Bit on Directories
We briefly mentioned that files have a user and group associated with them. Originally, it was just the user and group of whoever created them. But originally, a user could be in only one group at a time. BSD introduced the concept that a user could be in multiple groups simutaneously. So in BSD, which group was used? BSD decided to use the group of the directory that contained the newly created file.
Many modern versions of unix try to have it both ways. A newly created file gets the group of the user unless the directory has the setgid bit. In that case, the newly created file gets the group of the directory.
And there is an exception to that! Changing the owner or group of a file has security concerns. For that reason, some versions of unix will, optionally, prohibit a user other than root from changing the owner of a file. Additionally, a user is prohibited from changing the group of a file unless he is a member of the new group. This restriction will override the setgid bit on a directory if needed.
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UMASK(3) 1 UMASK(3)
umask - Changes the current umask
SYNOPSIS
int umask ([int $mask])
DESCRIPTION
umask(3) sets PHP's umask to $mask & 0777 and returns the old umask. When PHP is being used as a server module, the umask is restored when
each request is finished.
PARAMETERS
o $mask
- The new umask.
RETURN VALUES
umask(3) without arguments simply returns the current umask otherwise the old umask is returned.
EXAMPLES
Example #1
umask(3) example
<?php
$old = umask(0);
chmod("/path/some_dir/some_file.txt", 0755);
umask($old);
// Checking
if ($old != umask()) {
die('An error occurred while changing back the umask');
}
?>
NOTES
Note
Avoid using this function in multithreaded webservers. It is better to change the file permissions with chmod(3) after creating the
file. Using umask(3) can lead to unexpected behavior of concurrently running scripts and the webserver itself because they all use
the same umask.
PHP Documentation Group UMASK(3)