setting numerical file permissions with open

This is a discussion on setting numerical file permissions with open within the C Programming forums, part of the General Programming Boards category; Hi there, i'm writing to a log file using open: Code: log_file = open(log, O_RDWR | O_CREAT | O_APPEND, 0644); ...

  1. #1
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    setting numerical file permissions with open

    Hi there,

    i'm writing to a log file using open:
    Code:
    log_file = open(log, O_RDWR | O_CREAT | O_APPEND, 0644);
    as i understand it 0644 means owner can read and write, group and all can read only.

    why then, when the file is created, do it's permissions read as:
    Code:
    ---x-w-r-x    1 user user      120 Nov   8 10:17 logfile.log
    any ideas?

  2. #2
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    well, i think the mode parameter is only used when O_CREAT is specified.

    i.e. if the file does not exist, create it with the specified mode or use the default (the mode para is optional). The mode parameter is only used in this circumstance.

    if i do

    Code:
    chmod 0644 logfile.log
    the permissions are set correctly.

    you're right about opening with read/write - i'll change that.

    i presume unix numerical permissions are the same in linux!

  3. #3
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    solved the problem by using defined variables rather than numerical values:
    Code:
    log_file = open(log, O_CREAT | O_WRONLY | O_SYNC | O_APPEND, S_IRUSR | S_IWUSR | S_IRGRP);
    this creates a file with 0640 permissions.

    it important not to have a previous conflicting umask in the code - i'm not sure why!

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