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Full Discussion: Clear log file in use.
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
Old 06-19-2007
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
 

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KILL(1) 							   User Commands							   KILL(1)

NAME
kill - send a signal to a process SYNOPSIS
kill [options] <pid> [...] DESCRIPTION
The default signal for kill is TERM. Use -l or -L to list available signals. Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0. Alternate signals may be specified in three ways: -9, -SIGKILL or -KILL. Negative PID values may be used to choose whole process groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process itself and init. OPTIONS
<pid> [...] Send signal to every <pid> listed. -<signal> -s <signal> --signal <signal> Specify the signal to be sent. The signal can be specified by using name or number. The behavior of signals is explained in sig- nal(7) manual page. -l, --list [signal] List signal names. This option has optional argument, which will convert signal number to signal name, or other way round. -L, --table List signal names in a nice table. NOTES Your shell (command line interpreter) may have a built-in kill command. You may need to run the command described here as /bin/kill to solve the conflict. EXAMPLES
kill -9 -1 Kill all processes you can kill. kill -l 11 Translate number 11 into a signal name. kill -L List the available signal choices in a nice table. kill 123 543 2341 3453 Send the default signal, SIGTERM, to all those processes. SEE ALSO
kill(2), killall(1), nice(1), pkill(1), renice(1), signal(7), skill(1) STANDARDS
This command meets appropriate standards. The -L flag is Linux-specific. AUTHOR
Albert Cahalan <albert@users.sf.net> wrote kill in 1999 to replace a bsdutils one that was not standards compliant. The util-linux one might also work correctly. REPORTING BUGS
Please send bug reports to <procps@freelists.org> procps-ng October 2011 KILL(1)
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