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