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Full Discussion: Help in background process
Top Forums Shell Programming and Scripting Help in background process Post 302148874 by gus2000 on Tuesday 4th of December 2007 01:46:01 AM
Old 12-04-2007
Note that this will not work:

Code:
sub.ksh & >/tmp/logfile 2>&1

but this will:

Code:
sub.ksh >/tmp/logfile 2>&1 &

Redirection can get tricky, which is why I add this code to any of my scripts that run in the background or unattended:

Code:
exec >/tmp/${0##*/}.log 2>&1

After this line, all output (stdout and stderr) will go to a file in /tmp using the program basename with a ".log" extension. Don't try this from the command line!

UPDATE: I actually use a base set of code for background jobs:

Code:
# Send all output to a logfile and supress input
typeset LOG="/tmp/${0##*/}.out"
mv $LOG ${LOG}.old >/dev/null 2>&1
[[ -t 1 ]] && echo "Writing to logfile '$LOG'."
exec > $LOG 2>&1
exec < /dev/null 2<&1

Note that the shell expression "${0##*/}" is the same as "basename $0". Also, the "[[ -t ]]" should return TRUE when the process is attached to a terminal. In this case, it just prints a message about the logfile (instead of having the user wonder if the script is even running).

I also close stdin since an unattended script should never need input. For instance, if you have "grep $FILENAME" or "cat $FILENAME" and a bug has left $FILENAME unset, then the script would normally hang waiting for input from stdin. If that input is already /dev/null then the script can continue.
Last edited by gus2000; 12-05-2007 at 04:19 PM..
 

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LEARN ABOUT OPENSOLARIS

cachefslog

cachefslog(1M)						  System Administration Commands					    cachefslog(1M)

NAME

       cachefslog - Cache File System logging

SYNOPSIS

       cachefslog [-f logfile | -h] cachefs_mount_point

DESCRIPTION

       The  cachefslog	command displays where CacheFS statistics are being logged. Optionally, it sets where CacheFS statistics are being logged,
       or it halts logging for a cache specified by cachefs_mount_point. The cachefs_mount_point argument is a mount point of a cache file system.
       All file systems cached under the same cache as cachefs_mount_point will be logged.

OPTIONS

       The following options are supported. You must be super-user to use the -f and -h options.

       -f logfile    Specify the log file to be used.

       -h	     Halt logging.

OPERANDS

       cachefs_mount_point    A mount point of a cache file system.

USAGE

       See largefile(5) for the description of the behavior of cachefslog when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

EXAMPLES

       Example 1 Checking the Logging of a directory.

       The example below checks if the directory /home/sam is being logged:

	 example% cachefslog /home/sam
	 not logged: /home/sam

       Example 2 Changing the logfile.

       The example below changes the logfile of  /home/sam to /var/tmp/samlog:

	 example# cachefslog -f /var/tmp/samlog /home/sam
	 /var/tmp/samlog: /home/sam

       Example 3 Verifying the change of a logfile.

       The example below verifies the change of the previous example:

	 example% cachefslog /home/sam
	 /var/tmp/samlog: /home/sam

       Example 4 Halting the logging of a directory.

       The example below halts logging for the /home/sam directory:

	 example# cachefslog -h /home/sam
	 not logged: /home/sam

EXIT STATUS

       The following exit values are returned:

       0	   success

       non-zero    an error has occurred.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cachefsstat(1M), cachefswssize(1M), cfsadmin(1M), attributes(5), largefile(5)

DIAGNOSTICS

       Invalid path    It is illegal to specify a path within a cache file system.

SunOS 5.11							    7 Feb 1997							    cachefslog(1M)
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