trusty (2) umask.2.gz

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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), acl(5)

COLOPHON

       This  page  is  part  of  release 3.54 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/.