Semaphores and castles in Ubuntu

Question

I have a backup server that receives many rsyncconnections every hour . Since too many open instances rsynccan crash it, I want to limit the number of concurrent instances using Semaphore . What I mean is something like:

ssh root@backup_server "get_semaphore"     #Will hold until semaphore released
rsync -avzrL --super --delete local_directory root@backup_server:`localhost`

Any ideas?

Answer 1

In my opinion, you should look at limiting the number of simultaneous connections directly on the server side, so you do not need to do anything extreme on the client side:

(1) If you run rsync in daemon mode, an option exists for rsyncd.conf max connections.

(2) Linux iptables connlimit limit . , rsync , ssh, sshd.

(3) rsync script, -server, rsync , . script , N . .

#!/bin/bash

N=5

mutex_hold() {
    while ! mkdir /var/lock/rsync/mutex 2>/dev/null; do
       sleep 1
    done
}

mutex_release() {
    rmdir /var/lock/rsync/mutex
}

if [[ "$1" = "--server" ]]; then
    shopt -s nullglob

    while mutex_hold && A=(/var/lock/rsync/[0-9]*) && [[ "${#A[@]}" -ge "$N" ]] && mutex_release; do
       sleep 1
    done

    touch /var/lock/rsync/$$

    mutex_release

    rsync.bin "$@"

    rm -f /var/lock/rsync/$$
else
    rsync.bin "$@"
fi

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