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Gurity
Gurity

Reputation: 555

If a file is created by 'open' but without a 'mode' specified, what will the mode be?

I try to create a file "foo" in current dir like this:

open("foo", O_CREAT | O_EXCL | O_RDWR);

I did not give it a 'mode' for the third parameter, so what will it be? On my ubuntu 14.04, the mode for the this new file seems to be a random value. Isn't there any default value for the 'mode'?

Upvotes: 0

Views: 759

Answers (1)

rodrigo
rodrigo

Reputation: 98496

In the POSIX man 3p open it is not said very clearly, but in the Linux man 2 open:

int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);

mode specifies the permissions to use in case a new file is created. This argument must be supplied when O_CREAT or O_TMPFILE is specified in flags.

That is, if mode is not supplied when it should, the results are undefined.

Upvotes: 2

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