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August 18, 2003 - File Access Modes (Permissions) and umask

The umask command is used to set the file creation mask.  To put it another way, it controls what permissions will be granted to a newly created file or directory.

The syntax for the command is:

#umask mask
where mask is a three digit octal number, similar to the one used with the chmod command to set file permissions.  The first digit sets the mask for user, the second for group, and the third for other users.  Using umask without specifying a mask will display the current setting.

The value of mask represents what permissions will be revoked from the default file and directory permissions.  The default permissions for a file are rw-rw-rw- (or 666), and rwxrwxrwx (or 777) for a directory.

If the mask is set to 022, the write permission for group and other users will be revoked from the default permission settings:

# touch unixfile1
# ls -l unixfile1
-rw-rw-rw-   1   root   other      0   Aug 16 15:14 unixfile1
# umask 022
# touch unixfile2
# ls -l unixfile2
-rw-r--r--   1   root   other      0   Aug 16 15:15 unixfile2

Notice that the write permission for user was not changed because the first digit of the mask is 0.

The setting for umask is typically defined in the system startup file, but can be set to the value you desire by adding the umask command to your .profile.

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