01-20-2006
Quote:
Originally Posted by rmulchandani
I have a script which must not be run more than once at any given time. THis script will be scheduled to run every 20 mins as a cron job.
In my script can i have logic to say if this script is already running from the previous cron, then exit.
How do i go about doing that. If you describe the approach, can you please specify just the commands, which i can man to construct my approach.
Because I am not familiar with unix commands, if you tell me "find the file and do stuff..." i may not know the command to "find the file".
thanks!
write a tmp file to the /tmp directory.
have your script check to see if the file exists, if it does then don't run.
#!/bin/sh
# our tmpfile
tmpfile="/tmp/mytmpfile"
# check to see if it exists.
# if it does then exit script
if [[ -f ${tmpfile} ]]; then
echo script already running.
exit
fi
# it doesn't exist at this point so lets make one
touch ${tmpfile}
# do whatever now.
# end of script
rm ${tmpfile}
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LEARN ABOUT LINUX
tmpfile
TMPFILE(3) Linux Programmer's Manual TMPFILE(3)
NAME
tmpfile - create a temporary file
SYNOPSIS
#include <stdio.h>
FILE *tmpfile(void);
DESCRIPTION
The tmpfile() function opens a unique temporary file in binary read/write (w+b) mode. The file will be automatically deleted when it is
closed or the program terminates.
RETURN VALUE
The tmpfile() function returns a stream descriptor, or NULL if a unique filename cannot be generated or the unique file cannot be opened.
In the latter case, errno is set to indicate the error.
ERRORS
EACCES Search permission denied for directory in file's path prefix.
EEXIST Unable to generate a unique filename.
EINTR The call was interrupted by a signal.
EMFILE Too many file descriptors in use by the process.
ENFILE Too many files open in the system.
ENOSPC There was no room in the directory to add the new filename.
EROFS Read-only file system.
CONFORMING TO
SVr4, 4.3BSD, C89, C99, SUSv2, POSIX.1-2001.
NOTES
POSIX.1-2001 specifies: an error message may be written to stdout if the stream cannot be opened.
The standard does not specify the directory that tmpfile() will use. Glibc will try the path prefix P_tmpdir defined in <stdio.h>, and if
that fails the directory /tmp.
SEE ALSO
exit(3), mkstemp(3), mktemp(3), tempnam(3), tmpnam(3)
COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2008-07-14 TMPFILE(3)