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Full Discussion: How to check if a shell is already running ?
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
Old 02-12-2012
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 CENTOS

platform::shell

platform::shell(n)					       Tcl Bundled Packages						platform::shell(n)

__________________________________________________________________________________________________________________________________________________

NAME

       platform::shell - System identification support code and utilities

SYNOPSIS

       package require platform::shell ?1.1.4?

       platform::shell::generic shell
       platform::shell::identify shell
       platform::shell::platform shell
_________________________________________________________________

DESCRIPTION

       The platform::shell package provides several utility commands useful for the identification of the architecture of a specific Tcl shell.

       This  package  allows the identification of the architecture of a specific Tcl shell different from the shell running the package. The only
       requirement is that the other shell (identified by its path), is actually executable on the current machine.

       While for most platform this means that the architecture of the interrogated shell is identical to the architecture of  the  running  shell
       this  is  not generally true. A counter example are all platforms which have 32 and 64 bit variants and where a 64bit system is able to run
       32bit code. For these running and interrogated shell may have different 32/64 bit settings and thus different identifiers.

       For applications like a code repository it is important to identify the architecture of the shell which will  actually  run  the  installed
       packages, versus the architecture of the shell running the repository software.

COMMANDS

       platform::shell::identify shell
	      This command does the same identification as platform::identify, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::generic shell
	      This command does the same identification as platform::generic, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::platform shell
	      This command returns the contents of tcl_platform(platform) for the specified Tcl shell.

KEYWORDS

       operating system, cpu architecture, platform, architecture

platform::shell 						       1.1.4							platform::shell(n)
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