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cfile-ownership

How To Get The Owner Of A Unix File Using C

I'm trying the get owner's name of a Unix file using C. The only method I have found is to use stat() and then getpwuid(stat.st_uid). But, it only returns the first user name with that uid, where users in the password file can have the same uid. Obviously, this is unacceptable and cannot be trusted.

References:

Owner is recievd from password file: http://pubs.opengroup.org/onlinepubs/007904875/functions/getpwuid.html

Uid is found in password file: http://www.cyberciti.biz/faq/understanding-etcpasswd-file-format/

Unix allow multiple users to have same uid: http://www.e-reading.org.ua/htmbook.php/orelly/networking/puis/ch04_01.htm

Is there an accurate way or a lower level way, some kind of look up table that would guarantee me accurate results?

Solution

  • Unix file permissions work by using the UID. Usernames can't own files. Only UIDs can. So if a file belongs to a specific UID, than all users with that UID own the file.

    So it doesn't matter which username you get, since all users with that UID own the file.