Fw: Changing file ownership

[david at thekramers.net (David Kramer)]

I'm forwarding this one on because this is a subject that frustrates new *NIX users, 
and it was well-written.  Alpha geeks can delete it.

---- Original Message ----
From:		Linux Tips at TechRepublic.com
Date:		Tue 4/10/01 7:47
Subject:	Changing file ownership

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LINUX TIPS FOR APRIL 10, 2001

LINUX SKILLS REVIEW: CHANGING FILE OWNERSHIP
In the Linux filesystem, every file has an owner. Normally, the owner 
of a file is the user who creates the file. By default, you are the 
owner of all the files you create in your home directory. But there are 
times when you'll need to change a file's ownership. Should you need to 
do so, you can use the chown command. To change a file's ownership, 
switch to superuser by typing su and pressing [Enter].

The chown command uses the following syntax:

chown [ file owner] [ file name ]

To change the ownership of the file named document1.doc to a user named 
ferret, type the following code and press [Enter]:

chown ferret document1.doc 

As with most file utilities, you can specify a list of files or use 
wildcards, as in these examples:

chown ferret document1.doc document2.doc document3.doc 
chown ferret document?.doc

To change file ownership recursively (throughout the current directory 
and within all associated subdirectories), use the recursive (-R) 
option:

chown -R ferret *

The above example changes the ownership of all the files in the working 
directory and all associated subdirectories to ferret.

LINUX SKILLS REVIEW: CHANGING FILE PERMISSIONS
To change the permissions assigned to a file, use the chmod command. If 
you're the owner of the file, you can change the permissions while 
logged in to your user account. If the file belongs to someone else, 
you'll need to switch to superuser by typing su and pressing [Enter] at 
the command prompt.

Permissions affect the ability of the following user classes to access 
or change the file:

* u: User (owner of the file)

* g: Group (group owner of the file)

* o: Other (all other users)

* a: All (includes user, group, and others)

You can change permissions by specifying relative changes from the 
current permissions or by specifying absolute permissions. To specify 
relative changes to the current permissions, use the chmod command's 
symbolic mode. Absolute permissions can be set with the symbolic mode 
or the numeric mode. (A subsequent tip will cover absolute 
permissions.)

In the chmod command's symbolic mode, you can specify a user class, an 
operation, and a permission type. Here is how the operations are 
indicated:

* +: Adds the specified permission to the current setting

* =: Specifies an absolute permission setting (overrides the current 
permissions)

* -: Removes the specified permission from the current setting

Permission types include the following:

* r: Read permission (the file is read-only)

* w: Write permission (the file can be altered or deleted)

* x: Execute permission (the script or program can be executed)

In the symbolic mode, you use the chmod command with the following 
syntax:

chmod [ user class ] [ operation ] [ permission ] [ file ]

Examples:

* chmod g-w autobiography.doc: (removes Write permissions from 
autobiography.doc for members of the file owner's group)

* chmod a+r README.TXT: (makes README.TXT readable for all users)

These examples show how you can combine user classes and permissions:

* chmod ug+rx myscript: For the file owner and group owners, add Read 
and Execute permissions to the existing permissions for the file named 
myscript.

* chmod go-wx myscript: For group owners and others, remove Write and 
Execute permissions from the file named myscript.

In place of a single filename, you can supply a file list or use 
wildcards:

chmod u+x script1 script2 script3

or

chmod u+x script?

To change permissions throughout a directory and all associated 
subdirectories, you can use the recursive option (indicated by typing -
R or --recursive before the user class):

* chmod -R u+w *: Adds Write permissions to the owner's files 
throughout the working directory and all associated subdirectories

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