Clear log file in use. Post: 302122222

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Top Forums UNIX for Advanced & Expert Users Clear log file in use. Post 302122222 by porter on Tuesday 19th of June 2007 05:10:36 PM

06-19-2007

Registered User

Quote:

Originally Posted by coolbhai

So you meant to say." I cant do anything other than watch the log growing in size !!"

The problems are

(a) if the program always keeps the file open, eg it does not reopen on SIGHUP or every message or day.

(b) trying to clear it atomically

Two parts to my solution...

1. There is a UNIX API called "truncate" which will set a file to a certain number of bytes.

2. we can suspend and resume the program with signals SIGSTOP and SIGCONT

So the steps are

1. write a tiny C program that wraps up truncate

Code:

#include<unistd.h>
#include <errno.h>
int main(int argc,char **argv) {
int rc=0;
      while (--argc)
      {
            const char *p=*++argv;
            if (truncate(p,0UL)) {
                 perror(p);
                 rc=1;
            }
      }
      return rc;
}

2. do the following

kill -STOP pid-of-process
cp logfilename backup
truncate logfilename
kill -CONT pid-of-process

porter

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LEARN ABOUT DEBIAN

explain_truncate_or_die

explain_truncate_or_die(3)				     Library Functions Manual					explain_truncate_or_die(3)

NAME

       explain_truncate_or_die - truncate a file and report errors

SYNOPSIS

       #include <libexplain/truncate.h>
       void explain_truncate_or_die(const char *pathname, long long length);

DESCRIPTION

       The  explain_truncate_or_die  function  is  used to call the truncate(2) system call.  On failure an explanation will be printed to stderr,
       obtained from explain_truncate(3), and then the process terminates by calling exit(EXIT_FAILURE).

       This function is intended to be used in a fashion similar to the following example:
	      explain_truncate_or_die(pathname, length);

       pathname
	       The pathname, exactly as to be passed to the truncate(2) system call.

       length  The length, exactly as to be passed to the truncate(2) system call.

       Returns:
	       This function only returns on success.  On failure, prints an explanation and exits.

SEE ALSO

       truncate(2)
	       truncate a file to a specified length

       explain_truncate(3)
	       explain truncate(2) errors

       exit(2) terminate the calling process

COPYRIGHT

       libexplain version 0.52
       Copyright (C) 2008 Peter Miller

															explain_truncate_or_die(3)

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