Help scripting to start, check, and restart processes


 
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# 8  
Old 06-23-2011
Well I didn't actually lose sleep but thought of it. As I said, and tested, using -r started new screens each time chkscreen is ran if I was attached, because it checks for attachable screens and it is not tagged multiattach (maybe yours is in .screenrc?) But -S would just check if the session is running. I see no flaw in such method but maybe someone elses opinion would help.

But if you'd like to check PID, I can do that too. Screen would exit when jd.sh exits, so we'd have jd.sh report its PID with an echo $$ > $PIDFILE

I can write it up later. Mostly when I need my own service script like this, I'd copy one from a simple service in /etc/init.d. I am not famaliar with CentOS's as much, as I use Debian.
This User Gave Thanks to neutronscott For This Post:
# 9  
Old 06-23-2011
Seems I'm on to something, but can't get the correct PID. The PID that is saved is of the process that executes everything and not the running command's PID.

chkscr
Code:
#!/bin/sh
# chkscr: checks if the server is running.

CBPATH=/home/*user*/*serverdir*
SESSION="server1"
DAEMON="screen -d -m -S $SESSION /home/*user*/*serverdir*/exec"

if test -r $CBPATH/cb.pid; then
    CBPID=$(cat $CBPATH/cb.pid)
    if $(kill -CHLD $CBPID >/dev/null 2>&1)
    then
	exit 0
    fi
fi

echo "Restarting Server"
$DAEMON & echo $! > cb.pid

exec
Code:
#!/bin/bash

while true; do
java *server variables*
wait
done

When I type
# pidof /bin/bash /home/*user*/*serverdir*/exec
I'm given 2 PIDs. The first is for -bash and the second is the correct one. Maybe this command is returning the parent and child PIDs? I've been searching how to get a command's PID, but with no luck. When I type # ps x, I'm shown this:

PID...TTY...STAT...TIME...COMMAND
8658 pts/2 Ss+... 0:00 .. /bin/bash /home/*user*/*serverdir*/exec

This is the command's PID I need saved to cb.pid at the bottom of the chkscr script. Smilie
# 10  
Old 06-23-2011
screen will spawn a child, so I was thinking using $$ from 'exec'


You'll be checking if jd.sh is running. If it's running, java must be.. If it's not running, screen would exit (unless you add other windows I guess).

Remove the echo from chkscr and use

Code:
echo $$ >$CBPATH/cb.pid

at top of 'exec'
This User Gave Thanks to neutronscott For This Post:
# 11  
Old 06-23-2011
Finally got it with your help neutronscott. Thank you for all of your help. Smilie

I removed the " & echo $! > cb.pid" from the bottom of the chkscr script and added "ps -aef | grep -v grep | grep '/bin/bash /home/*user*/*serverdir*/exec' | awk '{print $2}' > cb.pid" to the next line.

Now it runs perfectly.

---------- Post updated at 04:38 PM ---------- Previous update was at 03:25 PM ----------

It's not working correctly. Spoke too soon, because my test didn't run long enough. It keeps making chkscr and exec processes. The check in the chkscr script is invalid.

I'm now looking for a check that checks the value in the file cb.pid to the actual PID of the process.

I can get the actual value of the processes PID by using "CBPID=$(ps -aef | grep -v grep | grep '/bin/bash /home/*user*/*serverdir*/exec' | awk '{print $2}')".

I can't find how to extract the PID number stored in the cb.pid file and make a valid "if actual PID = file's PID then end" statement.

Any help would be greatly appreciated.

Last edited by MacG32; 06-23-2011 at 06:56 PM..
# 12  
Old 06-23-2011
I thought using screen -ls was more elegant. This is what I came up with:

Code:
#!/bin/sh
# chkscreen: checks if a screen session is running.
WORKINGDIR=/home/mute/test
PIDFILE=cb.pid
SESSION="server1"
DAEMON="/home/mute/test/java-daemon.sh"

is_running()
{
    pid=$1
    name=$2
    [ -z "$pid" ] && return 1
    [ ! -d /proc/$pid ] &&  return 1
    cmd=`cat /proc/$pid/cmdline | tr "\000" "\n"|tail -n 1 |cut -d : -f 1`
    [ "$cmd" != "$name" ] &&  return 1
    return 0
}

# does the session exist?
#screen -S $SESSION -ls -q 2>&1 >/dev/null

# check java-daemon.sh's pid instead?
pid=$(cat $PIDFILE 2>/dev/null)
is_running "$pid" "$DAEMON"

if [ $? != 0 ]; then
        echo "Restarting $DAEMON"
        screen -d -m -S $SESSION $DAEMON
fi

Code:
#!/bin/sh
# java-daemon.sh: keeps restarting a buggy server... ;)

WORKINGDIR=/home/mute/test
PIDFILE=cb.pid

cd $WORKINGDIR
echo $$ >$PIDFILE

while true; do
top
done


or a more simple way without checking that it is the correct command running (it's not often the PIDs wrap around and get used for something else...?)

Code:
# check java-daemon.sh's pid instead?
pid=$(cat $PIDFILE 2>/dev/null)
kill -0 $pid 2>/dev/null

if [ "$?" != 0 ]; then
        echo "Restarting $DAEMON"
        screen -d -m -S $SESSION $DAEMON
fi

This User Gave Thanks to neutronscott For This Post:
# 13  
Old 06-24-2011
After extensive testing, it's finally all worked out.

Both files are saved in the server's directory and a crontab job running every minute with * * * * * /home/user/serverdir/chkscr >/dev/null 2>&1
here's the finished scripts.

chkscr
Code:
#!/bin/bash
# chkscr: Checks if server is running, if not, restarts it

# screen name
SESSION="server1"

# screen session and exec script
DAEMON="screen -d -m -S $SESSION /home/user/serverdir/exec"

# Gets exec's PID
PROPID=$(ps -aef | grep -v grep | grep '/bin/bash /home/user/serverdir/exec' | awk '{print $2}')

# Get PID value from file
read val < cb.pid

# Checks if exec's PID and file PID are same, sends message, then exits
if [ "$PROPID" -eq "$val" ]; then
screen -S $SESSION -X exec .! echo 'message Test complete.'
exit 0
fi

# If above check fails, deletes PID file
rm cb.pid

# Sends message, restarts server, remakes PID file with exec's PID for above check
echo "Restarting the server now."
$DAEMON
ps -aef | grep -v grep | grep '/bin/bash /home/user/serverdir/exec' | awk '{print $2}' > cb.pid

exec
Code:
#!/bin/bash
# exec: Starts the server from inside the screen and restarts it, if stopped

while true; do
java server variables
wait
done

Thanks neutronscott for all of your help and suggestions.

Last edited by MacG32; 06-24-2011 at 05:10 PM..
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