A script for syncing files and directories between two trusted servers (auto ssh login) using inotify. Far from perfect but does the job and a hell lot faster and more responsive than rsync.

Few notes for implementing:

• Make sure you have inotifywait command on the machine.
• Create /usr/bin/sys_admin/syncer.list with a directory/file per line.
• Start debugging :D.

Improved

Fixed some bugs when working on files using winscp and added support for file/dir moves/rename and ownership/permission sync.

Note: required deletion from move operations is delayed until the next update.

#!/bin/bash
# this script requires inotifywait, on debian: apt-get install inotify

PATH="$PATH:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/sys_admin/"

debug=0  # set to 1 for debug only mode, no operation will be performed
files_list="/usr/bin/sys_admin/syncer.list" # dir list, one per line, with trailing slash, no blank lines
target="target_server"
pid_file="/var/run/syncer.pid"
err_log="/var/log/syncer.err"
lock_file="/var/log/syncer.lock"
move_interval=2

check(){
        if [ ! -e $files_list ]; then
                echo "directoris file not found ($files_list)"
                exit 6
        fi
        if ! ping -c1 $target &>/dev/null; then
                echo "target unreacable ($target)"
                exit 7
        fi
}

create_dir(){
        touch $lock_file
        attrib_get $1
        (($debug)) &&\
                echo "ssh $target \"mkdir $1; chmod $perm $1; chown $own $1\";" ||\
                ssh $target "mkdir $1; chmod $perm $1; chown $own $" </dev/null
        rm -f $lock_file
}

remove_dir(){
        touch $lock_file
        (($debug)) &&\
                echo "ssh $target \"rmdir $1\"" ||\
                ssh $target "rmdir $1" </dev/null
        rm -f $lock_file
}

move_file(){
        touch $lock_file
        attrib_get $2
        (($debug)) &&\
                echo "ssh $target \"mv $1 $2; chmod $perm $2; chown $own $2;\"" ||\
                ssh $target "mv $1 $2; chmod $perm $2; chown $own $2;"
        rm -f $lock_file
}

remove_file(){
        touch $lock_file
        (($debug)) &&\
                echo "ssh $target \"rm $1\"" ||\
                ssh $target "rm $1" </dev/null
        rm -f $lock_file
}

copy_file(){
        touch $lock_file
        attrib_get $1
        (($debug)) &&\
                echo "scp $1 $target:$1" ||\
                scp $1 $target:$1
        attrib_do $1
        rm -f $lock_file
}

attrib_get(){
        touch $lock_file
        perm=`stat -c "%a" $1`
        own="`stat -c \"%U.%G\" $1`"
        rm -f $lock_file
}

attrib_do(){
        touch $lock_file
        (($debug)) &&\
                echo "ssh $target \"chmod $perm $1; chown $own $1\"" ||\
                ssh $target "chmod $perm $1; chown $own $1" </dev/null
        rm -f $lock_file
}

start(){
        /usr/bin/inotifywait -rm --timefmt "%s" --format "%w%f %e %T" -e create -e close_write -e delete -e attrib -e move --fromfile $files_list 2>/dev/null | while read file event time; do
                (($debug)) && echo +++++++ $file -- $event -- $time
                if [ "x$holder" != "x" ]; then
                        read stamp tmp_file tmp_event <<< "$holder"
                        if [ $((`date +%s`-$stamp)) -gt $move_interval ]; then
                                case $tmp_event in
                                         MOVED_FROM,ISDIR) remove_dir $tmp_file;;
                                         MOVED_FROM)               remove_file $tmp_file;;
                                esac
                                holder=""
                        fi
                fi
                case $event in
                        CLOSE_WRITE,CLOSE)   copy_file $file;;
                        CREATE)                      copy_file $file;; # needed for handling winscp
                        DELETE)                      remove_file $file;;
                        CREATE,ISDIR)                create_dir $file;;
                        DELETE,ISDIR)                remove_dir $file;;
                        ATTRIB*)             attrib_get $file; attrib_do $file;;
                        MOVED_FROM*)
                                        if [ "x$holder" == "x" ]; then
                                                holder="`date +%s` $file $event"
                                                (($debug)) && echo "holder: $holder"
                                        else
                                                read stamp tmp_file tmp_event <<< "$holder"
                                                case $tmp_event in
                                                         MOVED_FROM,ISDIR)       remove_dir $tmp_file;;
                                                         MOVED_FROM)             remove_file $tmp_file;;
                                                esac
                                                holder="`date +%s` $file $event"
                                                (($debug)) && echo "holder: $holder"
                                        fi
                                        ;;
                        MOVED_TO*)
                                        if [ "x$holder" == "x" ]; then
                                                case $event in
                                                        MOVED_TO,ISDIR)  create_dir $file;;
                                                        MOVED_TO)        copy_file $file;;
                                                esac
                                        else
                                                read stamp tmp_file tmp_event <<< "$holder"
                                                move_file $tmp_file $file
                                                holder=""
                                        fi
                                        ;;
                esac
        done &> /dev/null
}

stop(){
        while true; do
                kill `cat $pid_file 2>/dev/null` &>/dev/null && rm -f $pid_file &> /dev/null
                if [ ! -e $lock_file ]; then
                        return 0
                else
                        echo -n "."
                        sleep 2
                fi
        done
}

case $1 in
        start)         echo -n "Starting syncer service... "
                        if [ -f $pid_file ] && ((`ps awux | grep -v grep | grep -c inotifywait`)); then
                                echo " already running: pid file found ($pid_file) and an inotifywait process is running"
                                exit 1
                        elif [ -f $pid_file ]; then
                                echo -n "(stale pid file) "
                        fi
                        check
                        start&
                        pid="$!"
                        ps --ppid $pid -o pid,cmd | grep inotifywait | awk '{print $1}' > $pid_file
                        echo "Started"
                        ;;
        stop)          echo -n "Stopping syncer service... "
                        if [ -e $pid_file ]; then
                                stop
                                echo "Stopped"
                                exit 0
                        else
                                echo "pid file not found"
                                exit 2
                        fi
                        ;;
        restart)       $0 stop
                        $0 start
                        exit 0
                        ;;
        sync)          $0 status; st=$?
                        ((! $st)) && $0 stop
                        echo "Running initial sync:"
                        cat $files_list | while read dir; do
                                echo -n "  Initial sync for $dir"
                                rsync -ar -e ssh $dir $target:$dir &&\
                                echo " Done" ||\
                                echo " Error"
                        done
                        ((! $st)) && $0 start
                        ;;
        status)                echo -n "Getting status for syncer service... "
                        pid=`cat $pid_file 2>/dev/null`
                        if [ -f $pid_file ] && ((`ps awux | grep -v grep | egrep -c "$pid.*inotifywait"`)); then
                                echo "running (pid $pid)"
                                exit 0
                        elif [ -f $pid_file ]; then
                                echo "not runing (pid file found $pid)"
                                exit 3
                        elif ((`ps awux | grep -v grep | egrep -c "$pid.*inotifywait"`)); then
                                echo "not running (inotifywait procs found)"
                                exit 4
                        else
                                echo "not running"
                                exit 5
                        fi
                        ;;
        --help|-h)     echo "Syntax: $0 <start|stop|restart|status|sync>"
                        ;;
        *)             echo "Syntax error"
                        $0 -h
                        ;;
esac

Older version

#!/bin/bash
# this script requires inotifywait

PATH="$PATH:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

debug=0
files_list="/usr/bin/sys_admin/syncer.list"
target="1.1.1.0"
pid_file="/var/run/syncer.pid"
lock_file="/var/run/syncer.lock"
err_log="/var/log/syncer.err"

check(){
        if [ ! -e $files_list ]; then
                echo "directoris file not found ($files_list)"
                exit 3
        fi
        if ! ping -c1 $target &>/dev/null; then
                echo "target unreacable ($target)"
                exit 4
        fi
}
start(){
        /usr/bin/inotifywait -rm --timefmt "%s" --format "%w%f %e %T" -e create -e modify -e delete --fromfile $files_list 2>/dev/null | while read file event time; do
                (($debug)) && echo +++++++ $file -- $event -- $time
                case $event in
                        CREATE|MODIFY)  (($debug)) && echo "scp $file $target:$file"
                                        touch $lock_file
                                        scp $file $target:$file
                                        rm -f $lock_file
                                        ;;
                        DELETE)         (($debug)) && echo "ssh $target \"rm $file\""
                                        touch $lock_file
                                        ssh $target "rm $file" </dev/null
                                        rm -f $lock_file
                                        ;;
                        CREATE,ISDIR)   (($debug)) && echo "ssh $target \"mkdir $file\""
                                        touch $lock_file
                                        ssh $target "mkdir $file" </dev/null
                                        rm -f $lock_file
                                        ;;
                        DELETE,ISDIR)   (($debug)) && echo "ssh $target \"rmdir $file\""
                                        touch $lock_file
                                        ssh $target "rmdir $file" </dev/null
                                        rm -f $lock_file
                                        ;;
                esac
        done &> /dev/null #2>&1 | sed "s#^#`date` -- #" > $err_log
}

stop(){
        while true; do
                kill `cat $pid_file` &>/dev/null && rm -f $pid_file &> /dev/null
                if [ ! -e $lock_file ]; then
                        return 0
                else
                        echo -n "."
                        sleep 2
                fi
        done
}

case $1 in
        start)          echo -n "Starting syncer service... "
                        if [ -f $pid_file ] && ((`ps awux | grep -v grep | grep -c inotifywait`)); then
                                echo " already running: pid file found ($pid_file) and an inotifywait process is running"
                                exit 1
                        elif [ -f $pid_file ]; then
                                echo -n "(stale pid file) "
                        fi
                        check
                        start&
                        pid="$!"
                        ps --ppid $pid -o pid,cmd | grep inotifywait | awk '{print $1}' > $pid_file
                        echo "Started"
                        ;;
        stop)           echo -n "Stopping syncer service... "
                        if [ -e $pid_file ]; then
                                stop
                                echo "Stopped"
                                exit 0
                        else
                                echo "pid file not found"
                                exit 2
                        fi
                        ;;
        restart)        $0 stop
                        $0 start
                        exit 0
                        ;;
        status)         echo -n "Getting status for syncer service... "
                        pid=`cat $pid_file 2>/dev/null`
                        if [ -f $pid_file ] && ((`ps awux | grep -v grep | egrep -c "$pid.*inotifywait"`)); then
                                echo "running (pid $pid)"
                                exit 0
                        elif [ -f $pid_file ]; then
                                echo "not runing (pif file found $pid)"
                                exit 0
                        elif ((`ps awux | grep -v grep | egrep -c "$pid.*inotifywait"`)); then
                                echo "not running (inotifywait procs found)"
                                exit 0
                        else
                                echo "not running"
                                exit 0
                        fi
                        ;;
        --help|-h)      echo "Syntax: $0 <start|stop|restart|status>"
                        ;;
        *)              echo "Syntax error"
                        $0 -h
                        ;;
esac

TODO

• Add help and documentation
• Add a background proc for MOVED_FROM timeouts