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https://issues.apache.org/jira/browse/MAPREDUCE-4485?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422797#comment-13422797
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Todd Lipcon commented on MAPREDUCE-4485:
----------------------------------------
When you fork, Java already takes care of closing all the open file
descriptors. See UNIXProcess_md.c
> container-executor should deal with file descriptors better
> -----------------------------------------------------------
>
> Key: MAPREDUCE-4485
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4485
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: nodemanager
> Reporter: Colin Patrick McCabe
> Priority: Minor
>
> container-executor.c contains the following code:
> {code}
> fclose(stdin);
> fflush(LOGFILE);
> if (LOGFILE != stdout) {
> fclose(stdout);
> }
> if (ERRORFILE != stderr) {
> fclose(stderr);
> }
> if (chdir(primary_app_dir) != 0) {
> fprintf(LOGFILE, "Failed to chdir to app dir - %s\n", strerror(errno));
> return -1;
> }
> execvp(args[0], args);
> {code}
> Whenever you open a new file descriptor, its number is the lowest available
> number. So if {{stdout}} (fd number 1) has been closed, and you do
> open("/my/important/file"), you'll get assigned file descriptor 1. This
> means that any printf statements in the program will be now printing to
> /my/important/file. Oops!
> The correct way to get rid of stdin, stdout, or stderr is not to close them,
> but to make them point to /dev/null. {{dup2}} can be used for this purpose.
> Another thing we should be doing in container-executor.c is closing any file
> descriptors we don't need. Because container-executor was forked off of the
> JVM, any file that was open at the time the JVM called fork() will also be
> open for us. These FDs will continue to be open even after the {{execve}},
> unless we close them manually. This could be both a resource leak and a
> security breach.
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