linux C语言umask()函数

Posted 2022-06-08 Dontla

文章目录

• • man 2 umask

man 2 umask

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

NAME
       umask - set file mode creation mask	//设置文件模式创建掩码

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.
       //umask() 将调用进程的文件模式创建掩码 (umask) 设置为 mask & 0777（即仅使用掩码的文件权限位），并返回掩码的先前值。

       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).
       //umask 由 open(2)、mkdir(2) 和其他创建文件的系统调用使用，以修改放置在新创建的文件或目录上的权限。
        //具体来说，umask 中的权限从 open(2) 和 mkdir(2) 的 mode 参数关闭。

       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:
       //或者，如果父目录有默认 ACL（参见 acl(5)），则忽略 umask，继承默认 ACL，根据继承的 ACL 设置权限位，模式参数中缺少的权限位被关闭。
		//例如，以下默认 ACL 等效于 umask 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--).
       //将此默认 ACL 的效果与模式参数 0666 (rw-rw-rw-) 相结合，生成的文件权限将为 0644 (rw-r--r--)。

       The constants that should be used to specify mask are described under stat(2).
       //用于指定掩码的常量在 stat(2) 中进行了描述。

       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:
       //进程 umask 的典型默认值为 S_IWGRP | S_IWOTH（八进制 022）。 
       //在通常情况下 open(2) 的 mode 参数被指定为：

           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:
       //（八进制 0666）创建新文件时，生成文件的权限将是：

           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.
       //这个系统调用总是成功并且返回之前的掩码值。

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

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 4.04 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                                                                       2015-08-08                                                                    UMASK(2)
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