Unix Tutorial

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Permissions

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Permissions and Ownerships

There are three primary types of permission for files: read,write and execute.If no letter is present then it is substituted by a dash -. The dash means that this type of permission is not granted whether it be in the r, w or x position.The first column is broken down into four sub columns. The first sub column is one character long the second, third and fourth are all three characters long for a total of ten characters.The table below is a reflection of the four columns.

File/Directory	User	Group	Other
d	rwx	r-x	r--

The most common file permissions are

Permission	Meaning
---	No access is allowed
r--	Read only access
r-x	Read and execute access, for programs and shell scripts
rw-	Read and write access, for files
rwx	All access allowed, for programs

If the permission of the directory is write then you can add new items and remove items in the directory.

chmod command enables you to specify permissions in two different ways.

type %chmod [permission level] name_of _file.
Check option buttons

Common permissions and their numeric equivalents

Permission	Numeric	Used with
---\|---\|---	000	All types
r--\|---\|---	400	Files
r--\|r--\|r--	444	Files
rw-\|---\|---	600	Files
rw-\|r--\|r--	644	Files
rw-\|rw-\|r--	664	Files
rw-\|rw-\|rw-	666	Files
rwx\|---\|---	700	Programs and Directories
rwx\|r-x\|---	750	Programs and Directories
rwx\|r-x\|r-x	755	Programs and Directories