1UMASK(2)                   Linux Programmer's Manual                  UMASK(2)
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NAME

6       umask - set file mode creation mask
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SYNOPSIS

9       #include <sys/types.h>
10       #include <sys/stat.h>
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12       mode_t umask(mode_t mask);
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DESCRIPTION

15       umask()  sets  the calling process's file mode creation mask (umask) to
16       mask & 0777 (i.e., only the file permission bits of mask are used), and
17       returns the previous value of the mask.
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19       The  umask  is  used  by open(2), mkdir(2), and other system calls that
20       create files to modify the permissions placed on newly created files or
21       directories.   Specifically,  permissions  in  the umask are turned off
22       from the mode argument to open(2) and mkdir(2).
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24       The constants that should be used to specify mask are  described  under
25       stat(2).
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27       The  typical  default  value for the process umask is S_IWGRP | S_IWOTH
28       (octal 022).  In the usual case where the mode argument to  open(2)  is
29       specified as:
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31           S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH
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33       (octal 0666) when creating a new file, the permissions on the resulting
34       file will be:
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36           S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
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38       (because 0666 & ~022 = 0644; i.e., rw-r--r--).
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RETURN VALUE

41       This system call always succeeds and the previous value of the mask  is
42       returned.
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CONFORMING TO

45       SVr4, 4.3BSD, POSIX.1-2001.
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NOTES

48       A  child  process created via fork(2) inherits its parent's umask.  The
49       umask is left unchanged by execve(2).
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51       The umask setting also affects the permissions assigned  to  POSIX  IPC
52       objects  (mq_open(3), sem_open(3), shm_open(3)), FIFOs (mkfifo(3)), and
53       UNIX domain sockets (unix(7)) created by the process.  The  umask  does
54       not  affect the permissions assigned to System V IPC objects created by
55       the process (using msgget(2), semget(2), shmget(2)).
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SEE ALSO

58       chmod(2), mkdir(2), open(2), stat(2), acl(5)
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COLOPHON

61       This page is part of release 3.53 of the Linux  man-pages  project.   A
62       description  of  the project, and information about reporting bugs, can
63       be found at http://www.kernel.org/doc/man-pages/.
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67Linux                             2008-01-09                          UMASK(2)
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