fork processes

Shell Programming and Scripting
1

Hi,

How to count how many processes opened by fork function in perl.

Thanks

2

Hi Anjan1,

fork function creates one additional process. Check the return value, the child pid for the parent and 0 for the child. To count them use a variable, like

Regards,
Birei

3

Can someone also tell me how to limit number of forked processes in perl

4

You limit it by not forking when there's too many...

Don't you already have a thread about this?

5

Actually, i have 10 hosts, 1 thread should do ssh for 5 hosts and get uptime result and 2 thread should do ssh for other 5 hosts.

How can we achieve this?

6

Does it have to be perl? This would be much simpler in shell I think, to pipe multiple processes together, and prevent competition between two processes trying to read the same file... This is the kind of thing shell is made for.

7

Can you tell me in shell how do it then? some example

8 
$ cat ssh.sh

#!/bin/bash

MAXPROCS=2
PROCS=$(seq 1 $MAXPROCS)

function ssh_hosts # Reads hosts from stdin, writes output to stdout
{
        while read HOST
        do
                ssh "$HOST" printf "$HOST" ';' uptime </dev/null
        done
}

# Loop until we run out of lines
while [ -z "$FINISHED" ]
do
        # Read a line for each thread and feed it into the right file
        for N in $PROCS
        do
                if read LINE
                then
                        echo "$LINE">>/tmp/$$-$N
                        continue
                fi

                FINISHED=1
                break
        done
done < hosts1

for N in $PROCS
do
        # Add these to the list of tempfiles to delete on exit
        FILES="$FILES /tmp/$$-out$N /tmp/$$-$N"

        # Make a process reading from /tmp/$$-$N and writing to /tmp/$$-out$N
        ssh_hosts < /tmp/$$-$N > /tmp/$$-out$N &
done

# Delete all temporary files on exit, even if we quit with ctrl-c
trap "rm -f $FIFOS $FILES" EXIT

wait    # Wait for readers to quit

cat /tmp/$$-out*      # Read all output to stdout

$ cat hosts1

172.16.0.154
172.16.0.62
172.16.0.222
172.16.0.182
172.16.0.90
172.16.0.226
172.16.0.118
172.16.0.158
172.16.0.50
172.16.0.130
172.16.0.86

$ ./ssh.sh

172.16.0.154 11:10:32 up 6 days, 21:36,  0 users,  load average: 0.01, 0.02, 0.00
172.16.0.222 11:18:44 up 15 days, 21:26,  0 users,  load average: 0.03, 0.03, 0.00
172.16.0.90 10:50:28 up 2 days, 26 min,  0 users,  load average: 0.06, 0.04, 0.00
172.16.0.118 11:04:55 up 12 days, 23:12,  0 users,  load average: 0.11, 0.07, 0.02
172.16.0.50 10:51:34 up 47 days, 19:47,  0 users,  load average: 0.04, 0.04, 0.00
172.16.0.86 11:02:14 up 22 days,  1:52,  0 users,  load average: 0.01, 0.01, 0.00
172.16.0.62 11:24:51 up 21 days,  2:27,  0 users,  load average: 0.00, 0.00, 0.00
172.16.0.182 10:15:50 up 2 days, 25 min,  0 users,  load average: 0.02, 0.04, 0.00
172.16.0.226 11:17:48 up 6 days, 21:37,  0 users,  load average: 0.00, 0.00, 0.00
172.16.0.158 11:21:46 up 2 days, 24 min,  0 users,  load average: 0.08, 0.02, 0.01
172.16.0.130 10:57:22 up 5 days, 19:42,  0 users,  load average: 0.00, 0.00, 0.00

$
1 Like
9

Thanks, can you tell me how to do it in perl.

10

how about my answer in the other thread you didn't read.

11

This is all becoming confusing. I'm closing this thread. Please continue in the other one.

Anjan1, you have now three threads with the same title. Please start using descriptive titles. Thanks.