umask(2) [linux man page]
UMASK(2) Linux Programmer's Manual UMASK(2) 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) COLOPHON
This page is part of release 3.27 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/. Linux 2008-01-09 UMASK(2)
Check Out this Related Man Page
umask(1) umask(1) NAME
umask - get or set the file mode creation mask SYNOPSIS
/usr/bin/umask [-S] [mask] sh umask [ooo] csh umask [ooo] ksh umask [-S] [mask] The umask utility sets the file mode creation mask of the current shell execution environment to the value specified by the mask operand. This mask affects the initial value of the file permission bits of subsequently created files. If umask is called in a subshell or separate utility execution environment, such as one of the following: (umask 002) nohup umask ... find . -exec umask ... it does not affect the file mode creation mask of the caller's environment. For this reason, the /usr/bin/umask utility cannot be used to change the umask in an ongoing session. Its usefulness is limited to checking the caller's umask. To change the umask of an ongoing session you must use one of the shell builtins. If the mask operand is not specified, the umask utility writes the value of the invoking process's file mode creation mask to standard out- put. sh The user file-creation mode mask is set to ooo. The three octal digits refer to read/write/execute permissions for owner, group, and other, respectively (see chmod(1), chmod(2), and umask(2)). The value of each specified digit is subtracted from the corresponding ``digit'' spec- ified by the system for the creation of a file (see creat(2)). For example, umask 022 removes write permission for group and other. Files (and directories) normally created with mode 777 become mode 755. Files (and directories) created with mode 666 become mode 644). o If ooo is omitted, the current value of the mask is printed. o umask is recognized and executed by the shell. o umask can be included in the user's .profile (see profile(4)) and invoked at login to automatically set the user's permissions on files or directories created. csh See the description above for the Bourne shell (sh)umask built-in. ksh The user file-creation mask is set to mask. mask can either be an octal number or a symbolic value as described in chmod(1). If a symbolic value is given, the new umask value is the complement of the result of applying mask to the complement of the previous umask value. If mask is omitted, the current value of the mask is printed. The following option is supported: -S Produces symbolic output. The default output style is unspecified, but will be recognized on a subsequent invocation of umask on the same system as a mask operand to restore the previous file mode creation mask. The following operand is supported: mask A string specifying the new file mode creation mask. The string is treated in the same way as the mode operand described in the chmod(1) manual page. For a symbolic_mode value, the new value of the file mode creation mask is the logical complement of the file permission bits por- tion of the file mode specified by the symbolic_mode string. In a symbolic_mode value, the permissions op characters + and - are interpreted relative to the current file mode creation mask. + causes the bits for the indicated permissions to be cleared in the mask. - causes the bits of the indicated permissions to be set in the mask. The interpretation of mode values that specify file mode bits other than the file permission bits is unspecified. The file mode creation mask is set to the resulting numeric value. The default output of a prior invocation of umask on the same system with no operand will also be recognized as a mask operand. The use of an operand obtained in this way is not obsolescent, even if it is an octal number. OUTPUT
When the mask operand is not specified, the umask utility will write a message to standard output that can later be used as a umask mask operand. If -S is specified, the message will be in the following format: "u=%s,g=%s,o=%s ", owner permissions, group permissions, other permissions where the three values will be combinations of letters from the set {r, w, x}. The presence of a letter will indicate that the correspond- ing bit is clear in the file mode creation mask. If a mask operand is specified, there will be no output written to standard output. Example 1: Using the umask Command The examples in this section refer to the /usr/bin/umask utility and the ksh umask builtin. Either of the commands: umask a=rx,ug+w umask 002 sets the mode mask so that subsequently created files have their S_IWOTH bit cleared. After setting the mode mask with either of the above commands, the umask command can be used to write the current value of the mode mask: example$ umask 0002 The output format is unspecified, but historical implementations use the obsolescent octal integer mode format. example$ umask -S u=rwx,g=rwx,o=rx Either of these outputs can be used as the mask operand to a subsequent invocation of the umask utility. Assuming the mode mask is set as above, the command: umask g-w sets the mode mask so that subsequently created files have their S_IWGRP and S_IWOTH bits cleared. The command: umask --w sets the mode mask so that subsequently created files have all their write bits cleared. Notice that mask operands r, w, x, or anything beginning with a hyphen (-), must be preceded by - to keep it from being interpreted as an option. See environ(5) for descriptions of the following environment variables that affect the execution of umask: LANG, LC_ALL, LC_COL- LATELC_CTYPE, LC_MESSAGES, and NLSPATH. The following exit values are returned: 0 The file mode creation mask was successfully changed, or no mask operand was supplied. >0 An error occurred. See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ chmod(1), csh(1), ksh(1), sh(1), chmod(2), creat(2), umask(2), profile(4), attributes(5), environ(5), standards(5) 23 Jun 2005 umask(1)