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Full Discussion: How to check if process is running?
Special Forums UNIX and Linux Applications How to check if process is running? Post 302417072 by Corona688 on Wednesday 28th of April 2010 12:01:33 PM
Old 04-28-2010
A traditional way is for a process to create a PID file under /var/run/. I create it under /tmp/ just as an example that can run as any user. I also use a fifo as a lock file to prevent a race condition.

Code:
#!/bin/bash

function rm_pidfile
{
        rm -f /tmp/myscript.pid
}

function is_running
{
        # File does not exist, we can run
        [ -f /tmp/myscript.pid ] || return 1
        # Read PID from file
        read PID < /tmp/myscript.pid
        # File exists but process does not.
        [ -d /proc/${PID} ] || return 1
        return 0
}

# This guarantees other scripts will wait for each other
# before checking the pidfile.  otherwise one might create the PID
# file while we're not looking.
while ! mkfifo /tmp/myscript.lock 2> /dev/null
do
        sleep 1
done

# beyond this point, /tmp/myscript.lock exists and belongs to us.  Other
# instances of the script will loop.

if is_running
then
        echo "An instance(PID ${PID}) is already running"
        rm -f /tmp/myscript.lock
        exit 1
fi

# create PID file
echo "$$" > /tmp/myscript.pid

# make sure we delete it when the program quits
trap "rm_pidfile" EXIT

# Remove the lock file
rm -f /tmp/myscript.lock

# the rest of the code goes here

while true
do
        sleep 1
done

 

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LEARN ABOUT SUSE

sv

sv(8)							      System Manager's Manual							     sv(8)

NAME

       sv - control and manage services monitored by runsv(8)

SYNOPSIS

       sv [-v] [-w sec] command services

       /etc/init.d/service [-w sec] command

DESCRIPTION

       The sv program reports the current status and controls the state of services monitored by the runsv(8) supervisor.

       services consists of one or more arguments, each argument naming a directory service used by runsv(8).  If service doesn't start with a dot
       or slash and doesn't end with a slash, it is searched in the default services directory /etc/service/, otherwise relative  to  the  current
       directory.

       command is one of up, down, status, once, pause, cont, hup, alarm, interrupt, 1, 2, term, kill, or exit, or start, stop, restart, shutdown,
       force-stop, force-reload, force-restart, force-shutdown.

       The sv program can be sym-linked to /etc/init.d/ to provide an LSB init script interface.  The service to be controlled then  is  specified
       by the base name of the ``init script''.

COMMANDS

       status Report the current status of the service, and the appendant log service if available, to standard output.

       up     If the service is not running, start it.	If the service stops, restart it.

       down   If  the  service	is  running, send it the TERM signal, and the CONT signal.  If ./run exits, start ./finish if it exists.  After it
	      stops, do not restart service.

       once   If the service is not running, start it.	Do not restart it if it stops.

       pause cont hup alarm interrupt quit 1 2 term kill
	      If the service is running, send it the STOP, CONT, HUP, ALRM, INT, QUIT, USR1, USR2, TERM, or KILL signal respectively.

       exit   If the service is running, send it the TERM signal, and the CONT signal.	Do not restart the service.  If the service is	down,  and
	      no  log  service	exists, runsv(8) exits.  If the service is down and a log service exists, send the TERM signal to the log service.
	      If the log service is down, runsv(8) exits.  This command is ignored if it is given to an appendant log service.

       sv actually looks only at the first character of these commands.

   Commands compatible to LSB init script actions
       status Same as status.

       start  Same as up, but wait up to 7 seconds for the command to take effect.  Then report the status or  timeout.   If  the  script  ./check
	      exists  in the service directory, sv runs this script to check whether the service is up and available; it's considered to be avail-
	      able if ./check exits with 0.

       stop   Same as down, but wait up to 7 seconds for the service to become down.  Then report the status or timeout.

       reload Same as hup, and additionally report the status afterwards.

       restart
	      Send the commands term, cont, and up to the service, and wait up to 7 seconds for the service to restart.  Then report the status or
	      timeout.	 If  the script ./check exists in the service directory, sv runs this script to check whether the service is up and avail-
	      able again; it's considered to be available if ./check exits with 0.

       shutdown
	      Same as exit, but wait up to 7 seconds for the runsv(8) process to terminate.  Then report the status or timeout.

       force-stop
	      Same as down, but wait up to 7 seconds for the service to become down.  Then report the status, and on timeout send the service  the
	      kill command.

       force-reload
	      Send  the  service  the term and cont commands, and wait up to 7 seconds for the service to restart.  Then report the status, and on
	      timeout send the service the kill command.

       force-restart
	      Send the service the term, cont and up commands, and wait up to 7 seconds for the service to restart.  Then report the  status,  and
	      on  timeout  send the service the kill command.  If the script ./check exists in the service directory, sv runs this script to check
	      whether the service is up and available again; it's considered to be available if ./check exits with 0.

       force-shutdown
	      Same as exit, but wait up to 7 seconds for the runsv(8) process to terminate.  Then report the status, and on timeout send the  ser-
	      vice the kill command.

       try-restart
	      if the service is running, send it the term and cont commands, and wait up to 7 seconds for the service to restart.  Then report the
	      status or timeout.

   Additional Commands
       check  Check for the service to be in the state that's been requested.  Wait up to 7 seconds for the service to reach the requested  state,
	      then report the status or timeout.  If the requested state of the service is up, and the script ./check exists in the service direc-
	      tory, sv runs this script to check whether the service is up and running; it's considered to be up if ./check exits with 0.

OPTIONS

       -v     If the command is up, down, term, once, cont, or exit, then wait up to 7 seconds for the command to take effect.	 Then  report  the
	      status or timeout.

       -w sec Override the default timeout of 7 seconds with sec seconds.  This option implies -v.

ENVIRONMENT

       SVDIR  The environment variable $SVDIR overrides the default services directory /etc/service/.

       SVWAIT The  environment	variable $SVWAIT overrides the default 7 seconds to wait for a command to take effect.	It is overridden by the -w
	      option.

EXIT CODES

       sv exits 0, if the command was successfully sent to all services, and, if it was told to wait, the command has taken  effect  to  all  ser-
       vices.

       For  each  service  that  caused  an  error (e.g. the directory is not controlled by a runsv(8) process, or sv timed out while waiting), sv
       increases the exit code by one and exits non zero.  The maximum is 99.  sv exits 100 on error.

       If sv is called with a base name other than sv: it exits 1 on timeout or trouble sending the command; if the command is status, it exits  3
       if the service is down, and 4 if the status is unknown; it exits 2 on wrong usage, and 151 on error.

SEE ALSO

       runsv(8), chpst(8), svlogd(8), runsvdir(8), runsvchdir(8), runit(8), runit-init(8)

       http://smarden.org/runit/

AUTHOR

       Gerrit Pape <pape@smarden.org>

																	     sv(8)
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