установить маску создания режима файла (set file mode creation mask)
Имя (Name)
umask - set file mode creation mask
Синопсис (Synopsis)
#include <sys/stat.h>
mode_t umask(mode_t mask);
Описание (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).
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
in inode(7).
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--).
Возвращаемое значение (Return value)
This system call always succeeds and the previous value of the
mask is returned.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
Примечание (Note)
A child process created via fork(2) inherits its parent's umask.
The umask is left unchanged by execve(2).
It is impossible to use umask() to fetch a process's umask
without at the same time changing it. A second call to umask()
would then be needed to restore the umask. The nonatomicity of
these two steps provides the potential for races in multithreaded
programs.
Since Linux 4.7, the umask of any process can be viewed via the
Umask field of /proc/[pid]/status. Inspecting this field in
/proc/self/status allows a process to retrieve its umask without
at the same time changing it.
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)).
Смотри также (See also)
chmod(2), mkdir(2), open(2), stat(2), acl(5)
