umask(1) umask(1)
NAME [Toc] [Back]
umask - set or display the file mode creation mask
SYNOPSIS [Toc] [Back]
Set Mask
umask mask
Display Mask [Toc] [Back]
umask [-S]
DESCRIPTION [Toc] [Back]
The umask command sets the value of the file mode creation mask or
displays the current one. The mask affects the initial value of the
file mode (permission) bits for subsequently created files.
Setting the File Mode Creation Mask [Toc] [Back]
The umask mask command sets a new file mode creation mask for the
current shell execution environment. mask can be a symbolic or
numeric (obsolescent) value.
A symbolic mask provides a flexible way of modifying the mask
permission bits individually or as a group. A numeric mask specifies
all the permission bits at one time.
When a mask is specified, no output is written to standard output.
Symbolic Mask Value [Toc] [Back]
A symbolic mask replaces or modifies the current file mode creation
mask. It is specified as a comma-separated list of operations in the
following format. Whitespace is not permitted.
[who][operator][permissions][, ...]
The fields can have the following values:
who One or more of the following letters:
u Modify permissions for user (owner).
g Modify permissions for group.
o Modify permissions for others.
Or:
a Modify permissions for all (a = ugo).
operator One of the following symbols:
+ Add permissions to the existing mask for
who.
- Delete permissions from the existing
mask for who.
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umask(1) umask(1)
= Replace the existing mask for who with
permissions.
permissions One or more of the following letters:
r The read permission.
w The write permission.
x The execute/search permission.
If one or two of the fields are omitted, the following table applies:
Format Entered Effect | Input Equals
_________________________________________________________|_______________
who Delete current permissions for who | g g=
operator No action | - (none)
permissions Equal to: a+permissions | rw a+rw
who= Delete current permissions for who | u= u=
who+ No action | u+ (none)
who- No action | u- (none)
whopermissions Equal to: who=permissions | ux u=x
operatorpermissions Equal to: aoperatorpermissions | -rw a-rw
Numeric Mask Value (Obsolescent) [Toc] [Back]
A numeric mask replaces the current file mode creation mask. It is
specified as an unsigned octal integer, constructed from the logical
OR (sum) of the following mode bits (leading zeros can be omitted):
0400 ( a=rwx,u-r) Read by owner
0200 ( a=rwx,u-w) Write by owner
0100 ( a=rwx,u-x) Execute (search in directory) by owner
0040 ( a=rwx,g-r) Read by group
0020 ( a=rwx,g-w) Write by group
0010 ( a=rwx,g-x) Execute/search by group
0004 ( a=rwx,o-r) Read by others
0002 ( a=rwx,o-w) Write by others
0001 ( a=rwx,o-x) Execute/search by others
Displaying the Current Mask Value [Toc] [Back]
To display the current file mode creation mask value, use one of the
commands:
umask -S Print the current file mode creation mask in a
symbolic format:
u=[r][w][x],g=[r][w][x],o=[r][w][x]
The characters r (read), w (write), and x
(execute/search) represent the bits that are clear
in the mask for u (user/owner), g (group), and o
(other). All other bits are set.
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umask(1) umask(1)
umask Print the current file mode creation mask as an
octal value.
0[o][o][o]
The zero bits in the numeric value correspond to
the displayed r, w, and x permission characters in
the symbolic value. The one bits in the numeric
value correspond to the missing permission
characters in the symbolic value.
Depending on implementation, the display consists
of one to four octal digits; the first digit is
always zero (see DEPENDENCIES). The rightmost
three digits (leading zeros implied as needed)
represent the bits that are set or clear in the
mask.
Both forms produce output that can be used as the mask argument to set
the mask in a subsequent umask command.
General Operation [Toc] [Back]
When a new file is created (see creat(2)), each bit that is set in the
file mode creation mask causes the corresponding permission bit in the
the file mode to be cleared (disabled). Conversely, bits that are
clear in the mask allow the corresponding file mode bits to be enabled
in newly created files.
For example, the mask u=rwx,g=rx,o=rx (octal 022) disables group and
other write permissions. As a result, files normally created with a
file mode shown by the ls -l command as -rwxrwxrwx (octal 777) become
mode -rwxr-xr-x (octal 755); while files created with file mode -rw-
rw-rw- (octal 666) become mode -rw-r--r-- (octal 644).
Note that the file creation mode mask does not affect the set-user-id,
set-group-id, or "sticky" bits.
The file creation mode mask is also used by the chmod command (see
chmod(1)).
Since umask affects the current shell execution environment, it is
generally provided as a shell regular built-in (see DEPENDENCIES).
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 ...
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umask(1) umask(1)
it does not affect the file mode creation mask of the calling
environment.
The default mask is u=rwx,g=rwx,o=rwx (octal 000).
RETURN VALUE [Toc] [Back]
umask exits with one of the following values:
0 The file mode creation mask was successfully changed or no
mask operand was supplied.
>0 An error occurred.
EXAMPLES [Toc] [Back]
In these examples, each line show an alternate way of accomplishing
the same task.
Set the umask value to produce read and write permissions for the
file's owner and read permissions for all others (ls -l displays -rw-
r--r-- on newly created files):
umask u=rwx,g=rx,o=rx symbolic mode
umask a=rx,u+w symbolic mode
umask 022 numeric mode
Set the umask value to produce read, and write permissions for the
file's owner, read-only for others users in the same group, and no
access to others (-rw-r-----):
umask a-rwx,u+rw,g+r symbolic mode
umask u=rw,g=r,o= symbolic mode
umask ,u+rw,g+r symbolic mode
umask 137 numeric mode
Set the umask value to deny read, write, and execute permissions to
everyone (----------):
umask a= symbolic mode
umask 777 numeric mode
Add the write permission to the current mask for everyone (there is no
equivalent numeric mode):
umask a+w symbolic mode
WARNINGS [Toc] [Back]
If you set a mask that prevents read or write access for the user
(owner), many programs, such as editors, that create temporary files
will fail because they cannot access the file data.
DEPENDENCIES [Toc] [Back]
The umask command is implemented both as a separate executable file
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umask(1) umask(1)
(/usr/bin/umask) and as built-in shell commands.
POSIX Shell and Separate File [Toc] [Back]
All features are supported (see sh-posix(1)). The numeric mask
display uses a minimum of two digits.
Korn Shell [Toc] [Back]
The -S option is not supported in the Korn shell built-in command (see
ksh(1)). The numeric mask display uses a minimum of two digits.
C Shell [Toc] [Back]
The -S option and symbolic mask values are not supported in the C
shell built-in command (see csh(1)). The numeric mask display uses a
minimum of one digit.
SEE ALSO [Toc] [Back]
chmod(1), csh(1), ksh(1), sh-posix(1), sh(1), chmod(2), creat(2),
umask(2).
STANDARDS CONFORMANCE [Toc] [Back]
umask: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2
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