umask2 man page (was: Re: [PATCH v4 0/3] vfs: Define new syscall umask2 [formerly getumask])

[Richard W.M. Jones]

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



NAME
       umask, umask2 - get and set file mode creation mask

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>

       mode_t umask(mode_t mask);

       #define _GNU_SOURCE
       #include <fcntl.h>
       #include <sys/types.h>
       #include <sys/stat.h>

       mode_t umask2(mode_t mask, int flags);

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.

       If flags is 0, then umask2() is the same as umask().

       If flags is UMASK_GET_MASK then umask2() ignores the mask parameter and
       returns the process's current umask.  The process's current mask is not
       modified in this case.

       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).

       Alternatively, if the parent directory has a default ACL (see  acl(5)),
       the umask is ignored, the default ACL is inherited, the permission bits
       are set based on the inherited ACL, and permission bits absent  in  the
       mode  argument  are turned off.  For example, the following default ACL
       is equivalent to a umask of 022:

           u::rwx,g::r-x,o::r-x

       Combining the effect of this default ACL with a mode argument  of  0666
       (rw-rw-rw-), the resulting file permissions would be 0644 (rw-r--r--).

       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
       The  umask()  system call always succeeds and the previous value of the
       mask is returned.

       The umask2() system call returns the process's current  umask  on  sucâ
       cess.  On error it returns -1 and sets errno appropriately.

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 4.00 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       http://www.kernel.org/doc/man-pages/.



Linux                             2016-04-13                          UMASK(2)