What is the difference between Real UID and Effective UID in terms of file attributes

techie_san778 · 05-10-2013, 12:52 AM

Hello Everyone!!

1. What is the difference between the Real UID and Effective UID in terms of file attributes ? Can someone explain it with suitable example ?

2. If its possible, How to set the Effective UID of a file ?

pan64 · 05-10-2013, 12:57 AM

https://en.wikipedia.org/wiki/User_identifier
can you please explain 2

chrism01 · 05-10-2013, 01:12 AM

Files don't have that; they are process attributes eg
http://www.osso.nl/tech/blog/2012/08...euid-uid-euid/
http://notepad2.blogspot.com.au/2012...-in-linux.html
https://en.wikipedia.org/wiki/User_identifier

jpollard · 05-10-2013, 03:55 PM

Effective UID and Real UID are process attributes. A process may set (via a setuid or su) the effective UID - which is then used for general file access.

The Real UID is used when the process wants to restore its UID (doesn't happen very often as it is a bit awkward). The seteuid is allowed to be changed IF the real UID is root, OR the new effective UID is the same as the Real UID.

pan64 · 05-11-2013, 12:20 AM

actually you can set setuid and setgid bits on a file (on an executable), but I do not know what OP really meant. see: http://linux.die.net/man/1/chmod