04-11-2008
Quote:
If you were not allowed to change it under any circumstances, it ought to be impossible. But you can. However, you should be aware of the security implications. If you set it too loose, people will be creating private files in their home directories which are readable by anyone -- if that's acceptable then go ahead. (Setting it tighter than the default is usually not a problem.)
Sounds like you might be barking up the wrong tree, though. Could you describe what problem you are trying to solve? If you want files in a shared directory to be created with specific permissions, maybe your platform would offer a facility for this by other means (for example, by using the setgid bit on the directory, on some platforms).
i want to change the file permisiion without using any command.mean i want to change it using umask only.so i want to know without doing any calculation shall we come to know that what is the vlaue of file permission like is it 0666 or anyother.but without doing any calculation.we can do like this or not?
thats what i want to know
thank u
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UMASK(2) Linux Programmer's Manual UMASK(2)
NAME
umask - set file mode creation mask
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
mode_t umask(mode_t mask);
DESCRIPTION
umask() sets the calling process's file mode creation mask (umask) to mask & 0777 (i.e., only the file permission bits of mask are used),
and returns the previous value of the mask.
The umask is used by open(2), mkdir(2), and other system calls that create files to modify the permissions placed on newly created files or
directories. Specifically, permissions in the umask are turned off from the mode argument to open(2) and mkdir(2).
The constants that should be used to specify mask are described under stat(2).
The typical default value for the process umask is S_IWGRP | S_IWOTH (octal 022). In the usual case where the mode argument to open(2) is
specified as:
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH
(octal 0666) when creating a new file, the permissions on the resulting file will be:
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
(because 0666 & ~022 = 0644; i.e., rw-r--r--).
RETURN VALUE
This system call always succeeds and the previous value of the mask is returned.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
NOTES
A child process created via fork(2) inherits its parent's umask. The umask is left unchanged by execve(2).
The umask setting also affects the permissions assigned to POSIX IPC objects (mq_open(3), sem_open(3), shm_open(3)), FIFOs (mkfifo(3)), and
UNIX domain sockets (unix(7)) created by the process. The umask does not affect the permissions assigned to System V IPC objects created
by the process (using msgget(2), semget(2), shmget(2)).
SEE ALSO
chmod(2), mkdir(2), open(2), stat(2)
COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2008-01-09 UMASK(2)