Change permissions

Only the owner and root can change permissions for a file or directory.

The easiest way of changing permissions from the command line is to use the command $ chmod and specify the new permissions as a binary number.

Permissions written as rwxrw-r-- can also be written as a binary number.

For example: -rwxrw-r-- 1 user group 55 2009-09-29 20:43 filename
can be written as: -111110100 1 user group 55 2009-09-29 20:43 filename

Where rw-r-xr-- = 110101100

The binary is split into three parts: 110 101 100

And each part is summed using binary math:

• 000 = zero
• 001 = one
• 010 = two
• 011 = three
• 100 = four
• 101 = five
• 110 = six
• 111 = seven

When summed: rw-r-xr-- = 110101100 = 654

Now change file permissions with $ chmod

$ chmod 411 filename will change permissions to r----x--x

$ chmod -R 411 dirname Will change permissions recursively for all files in a directory, including subfolders.

Letters instead of binaries

It is also possible use chmod with letters to represent the permissions. Read is r , write is w and execute is x

$ chmod g+r filename Will give read permission to group.

To remove a permission, replace + with -

$ chmod g-x filename Will take away execute permission from group.

Use a for all, u for user, g for group and o for others.

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