How to check if a shell is already running ? Post: 302597832

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Operating Systems Solaris How to check if a shell is already running ? Post 302597832 by agama on Sunday 12th of February 2012 11:35:47 AM

02-12-2012

Registered User

I assume you have a long running script and are wanting to prevent a second copy from starting if the first is running. What is probably happening is that your test is seeing 'itself' in the output from ps and is claiming that another copy is already running.

When I have to ensure that the invocation of a script is the only one running I use a marker directory in /tmp. Only one process can create a directory, so if two are started at the same time then only one will 'win' and continue running. Further, I add some information to the directory so that when another detects one already running, it can verify that it is still running and allows itself to start if it finds a marker, but doesn't find an associated process.

Here's an example:

Code:

#!/usr/bin/env ksh

trap "rm -fr \${solo_mark:-nosuchfile}" EXIT            # remove our marker stuff at exit

cmd=${0##*/}
solo_mark=/tmp/$cmd.solo
if ! mkdir $solo_mark 2>/dev/null       # if two started at the same time only one will be successful
then
    sleep 1                             # if there was a collision, allow winner to set the info file
    read rinfo <$solo_mark/info
    echo "verification that '$rinfo' is still running"
    if ps -e -o pid,command |awk -v rinfo="$rinfo" '
        BEGIN { split( rinfo, a, " " ); }
        $1 == a[1] {
            if( rinfo == $0 )
                exit( 1 );
            next;
          }'
    then
        echo "marker exists, but not running; we continue"
    else
        echo "already running"
        exit 1;
    fi
else
    echo "not running"
fi
ps -o pid,command | grep "^[ ]*$$" >$solo_mark/info     # save our info for others to verify
 


# ------- do intended work here -----------------

The bit of extra work to save the info, and verify it, makes things easier following a system crash, or someone killing the process in such a way that the marker doesn't get removed.

Hope this helps.

Last edited by agama; 02-12-2012 at 12:39 PM.. Reason: formatting

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LEARN ABOUT SUNOS

shell

shell(1F)							   FMLI Commands							 shell(1F)

NAME

       shell - run a command using shell

SYNOPSIS

       shell command [command] ...

DESCRIPTION

       The  shell  function  concatenate  its arguments, separating each by a space, and passes this string to the shell ($SHELL if set, otherwise
       /usr/bin/sh).

EXAMPLES

       Example 1: A sample output of shell command.

       Since the Form and Menu Language does not directly support background processing, the shell function can be used instead.

       `shell "build prog > /dev/null &"`

       If you want the user to continue to be able to interact with the application while the background job is running, the  output  of  an  exe-
       cutable	run  by shell in the background must be redirected: to a file if you want to save the output, or to /dev/null if you don't want to
       save it (or if there is no output), otherwise your application may appear to be hung until the background job finishes processing.

       shell can also be used to execute a command that has the same name as an FMLI built-in function.

NOTES

       The arguments to shell will be concatenate using spaces, which may or may not do what is expected. The variables set in local  environments
       will not be expanded by the shell because "local" means "local to the current process."

ATTRIBUTES

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

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

SEE ALSO

       sh(1), attributes(5)

SunOS 5.10							    5 Jul 1990								 shell(1F)

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