Unix C, writing to file as non-owner 1

[lewisp]

Is it possible in C on Unix to write to a file not owned by the program executor, and the file has r--r--r-- privileges?

The reason I ask is because this is what SCCS seems to do and I want to do the same thing. All SCCS files are created with r--r--r-- privileges, but anyone using the SCCS commands can write their changes to the files. I had assumed it was to do with setting the effective user ID within the process, but the executor must have privilege to do this as well.

 

[hoinz]

If my understanding is correct, SCCS will not change an existing file. It will create a new temporary file, and in the end replace the old one by the temp file. Write permission in the directory is sufficient.
Have a look at man admin
or

http://tucupi.cptec.inpe.br/sx4/sx4man2/g1ab01e/chap8.html#8.6

hope this helps

 

[xwb]

It is something to do with the sticky bit but I can't remember what. It gives temporary privileges or allows you to run certain commands as a different usr

eg when you're changing your password: you are not privileged to write to /etc/passwd but it writes your new password to /etc/passwd.

 

[lewisp]

Thanks for the replies guys. The sticky bit is probably the professional way to go but the rename/replace option works a treat for me!

 

[Largins421]

Hello,

SCCS does indeed create it's own file. That is what the s.whatever file is. It contains not the complete file, but a history of all changes applied to for each version (delta) of the original file, and on a 'get' command, creates a new file containing all of the changes for the requested version.

Larry

 

[lewisp]

Thats right, and the s.<name> file is owned by the original creator and has r--r--r-- privileges assigned. I needed to know how someone other than the creator could modify the s.<name> file when it has read-only privs, like SCCS does.

The answer for me is exactly as hoinz suggests. Once copied, the new file has its privileges changed to match and then the owner is also set to be the original creator.

Simple really ).