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echo appends to a read-only file

 
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Top Forums UNIX for Dummies Questions & Answers echo appends to a read-only file
# 1  
Old 12-23-2009
echo appends to a read-only file
echo command can append to a read-only file too.

If the file is read-only, with w flag removed, then even echo should not be able to append to the file. But it is possible.

Can anybody explain the below behaviour?

Code:
/root > echo 'sample text' > file
/root > cat file
sample text
/root > ls -l file
-r--r--r--  1 root  wheel  12 Dec 23 15:04 file
/root > chmod -w file
/root > ls -l file
-r--r--r--  1 root  wheel  12 Dec 23 15:04 file
/root > echo 'trying to append' >> file
/root > cat file
sample text
trying to append

Last edited by pludi; 12-23-2009 at 05:47 AM.. Reason: code tags, please...
# 2  
Old 12-23-2009
Any command can modify a file, if the user is allowed to. And with only basic UNIX permissions, root can do anything, anytime. Try the same under a user account and you'll get an "permission denied" error.

If you want to prevent root from modifying certain files, look up how to implement ACLs for your platform.
# 3  
Old 12-23-2009
buddy, you have to understand this thing, root has all power.

For super user, the permission bits will not be cross checked, so not only echo, cat, other editors and anything can edit the files if you are working as super user.

From wiki:
Code:
root is the conventional name of the user who has all rights or permissions (to all files and programs)

 
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