Sometimes lsync stops working and the error message you receive is relating to increasing inotify watches.
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View Current config
<sxh bash>
cat /proc/sys/fs/inotify/max_user_watches
</sxh>
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To calculate an estimate on the inotify values you can run the following command:
<sxh bash>
find /var/www/vhosts/ -type d | wc -l | awk '{print $1" directories needs monitoring, set [ fs.inotify.max_user_watches = " $1*3" ]"}'
</sxh>
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To perm change the value:
<sxh bash>
echo "fs.inotify.max_user_watches=value >> /etc/sysctl.conf

sysctl -p /etc/sysctl.conf
</sxh>
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To see what is currently being used by inotify watches you can run:
<sxh bash>
for foo in /proc/*/fd/*; do readlink -f $foo; done |grep inotify |cut -d/ -f3 |xargs -I '{}' -- ps --no-headers -o '%p %U %c' -p '{}' |uniq -c |sort -nr
</sxh>