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Top Forums UNIX for Dummies Questions & Answers Unmask Post 302241701 by Grippo on Tuesday 30th of September 2008 03:41:50 AM

09-30-2008

Registered User

Quote:

Originally Posted by agasamapetilon

The mention command does a very simple thing. Actually with it you set the default permissions you want for files. It could be for every created file in the system or for a specific user session.

If you for example want for every single file only read permissions then you have to do this:

777(all permissions) - 444(read permissions) = 333, the umask for only readable permissions is: 333

Have a look here: Setting default permissions

umask (as its name says) is a mask and you have to remember that what you set is to be subtracted from 777 to get the require file creation permissions.

umask 000 - will mean created files have perms 777
umask 022 - will mean create files will have pwems 755

Grippo

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LEARN ABOUT LINUX

umask

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 3.27 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)