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Is it a possible hole of security having /tmp/ folder under user owner instead of root?

I have set it temporally under my user by mistake, after that its impossible to bring it back to root user: Ubuntu after that doesent recognize my session.

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I don't think there's an inherent risk if /tmp doesn't belong to root, but it should belong to root following best practices (it's a system directory).

Also, note that the /tmp directory permissions must have the sticky bit set:

drwxrwxrwt  4 root root  4096 2012-02-19 19:56 tmp

This way, files created in /tmp can be read and written only by the user that creates them. Not doing this is indeed a security risk as users could write or delete files that belong to other users or processes.

Regarding your session, I believe you should be able to solve this by changing the ownership from a console, while the X system is down (go to a TTY console with CTRL+ALT+F1, service lightdm stop (or service gdm stop), change ownership and reboot).

To change owner and permissions, you can use:

sudo chown root:root /tmp
sudo chmod 1777 /tmp
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my folder tmp/ is actually : drwxrwxr-x 13 papachan root 4096 2012-02-19 14:23 tmp actually iam able to resolve the session problem by starting Reconvery console and change my user PASSWD –  Papachan Feb 19 '12 at 19:41
    
maybe the problem session is another problem... now my /tmp folder belong to root user and with the correct permissions as you mentioned. and i can login to my session –  Papachan Feb 19 '12 at 19:45
1  
I updated my answer with the commands you can use to fix this. Make sure you reboot after the changes: in this case you want to be sure that everything remains correct after rebooting. –  jjmontes Feb 19 '12 at 19:46

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