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Full Discussion: umask
Top Forums UNIX for Advanced & Expert Users umask Post 302329772 by kurinchiblogger on Monday 29th of June 2009 11:12:26 AM
Old 06-29-2009
umask explanation

I thought to post the information related to umask which i have read it from sites so that it might be helpful to someone who comes across this thread ...

$ umask
022 (this is the default value in my system)

For files, the permission settings are 0666 and for directories it is 0777


Having known the umask value, try creating a directory and a file and check what the file settings are

$ mkdir tempdir1

$ ls -l
drwxr-xr-x 2 root root 4096 2009-06-29 10:42 tempdir1

$ touch tempfile1

$ ls -l
drwxr-xr-x 2 root root 4096 2009-06-29 10:42 tempdir1
-rw-r--r-- 1 root root 0 2009-06-29 10:43 tempfile1


Change the umask and again create a directory and a file and check the file permission settings

$ umask 027
$ umask
0027
$ mkdir tempdir2
$ ls -l
total 12
drwxr-x--- 2 root root 4096 2009-06-29 10:40 tempdir2

$ touch tempfile2
$ ls -l
drwxr-x--- 2 root root 4096 2009-06-29 10:40 tempdir2
-rw-r----- 1 root root 0 2009-06-29 10:40 tempfile2

Now, let us see how the file permission settings are calculated using boolean expression.

For the directories, you need to take the 1's complement of the umask value and perform a logical AND operation with 0777.

For e.g. consider the case where we have umask value of 027 - 0000 0000 0010 0111
1's complement of 027 - 1111 1101 1000

For directories perform logical AND operation with 0777 (0000 0111 0111 0111). So

1111 1101 1000 (1's complement of 027)
0111 0111 0111 (0777)
-------------------
0111 0101 0000 = 0750


For files, perfom logical AND operation with 0666 (0000 0110 0110 0110), so

1111 1101 1000 (1's complement of 027)
0110 0110 0110 (0666)
-------------------
0110 0100 0000 = 0640
 

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MKDIR(1)						    BSD General Commands Manual 						  MKDIR(1)

NAME
mkdir -- make directories SYNOPSIS
mkdir [-pv] [-m mode] directory_name ... DESCRIPTION
The mkdir utility creates the directories named as operands, in the order specified, using mode rwxrwxrwx (0777) as modified by the current umask(2). The options are as follows: -m mode Set the file permission bits of the final created directory to the specified mode. The mode argument can be in any of the formats specified to the chmod(1) command. If a symbolic mode is specified, the operation characters ``+'' and ``-'' are interpreted rela- tive to an initial mode of ``a=rwx''. -p Create intermediate directories as required. If this option is not specified, the full path prefix of each operand must already exist. On the other hand, with this option specified, no error will be reported if a directory given as an operand already exists. Intermediate directories are created with permission bits of rwxrwxrwx (0777) as modified by the current umask, plus write and search permission for the owner. -v Be verbose when creating directories, listing them as they are created. The user must have write permission in the parent directory. DIAGNOSTICS
The mkdir utility exits 0 on success, and >0 if an error occurs. SEE ALSO
rmdir(1) COMPATIBILITY
The -v option is non-standard and its use in scripts is not recommended. STANDARDS
The mkdir utility is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. HISTORY
A mkdir command appeared in Version 1 AT&T UNIX. BSD
January 25, 1994 BSD
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