example: prevent script from running in parallel to avoid races

diff --git a/odhcp6c-example-script.sh b/odhcp6c-example-script.sh
index 621525750bcdfaeb22244350643b6007265cc06c..a1fb0fc22f4752e0320fbd4d6e012e283afb5072 100755 (executable)
--- a/odhcp6c-example-script.sh
+++ b/odhcp6c-example-script.sh
@@ -6,7 +6,7 @@ update_resolv() {
        local dns="$2"
        
        (
-               flock -n 9
+               flock 9
                grep -v "#odhcp6c:$device:" /etc/resolv.conf > /tmp/resolv.conf.tmp
                for c in $dns; do
                        echo "nameserver $c #odhcp6c:$device:" >> /tmp/resolv.conf.tmp
@@ -131,23 +131,25 @@ teardown_interface() {
        update_resolv "$device" ""
 }
 
-case "$2" in
-       bound)
-               teardown_interface "$1"
-               setup_interface "$1"
-       ;;
-       informed|updated|rebound|ra-updated)
-               setup_interface "$1"
-       ;;
-       stopped|unbound)
-               teardown_interface "$1"
-       ;;
-       started)
-               teardown_interface "$1"
-       ;;
-esac
-
-# user rules
-[ -f /etc/odhcp6c.user ] && . /etc/odhcp6c.user
-
-exit 0
+(
+       flock 9
+       case "$2" in
+               bound)
+                       teardown_interface "$1"
+                       setup_interface "$1"
+               ;;
+               informed|updated|rebound|ra-updated)
+                       setup_interface "$1"
+               ;;
+               stopped|unbound)
+                       teardown_interface "$1"
+               ;;
+               started)
+                       teardown_interface "$1"
+               ;;
+       esac
+
+       # user rules
+       [ -f /etc/odhcp6c.user ] && . /etc/odhcp6c.user
+) 9>/tmp/odhcp6c.lock.$1
+rm -f /tmp/odhcp6c.lock.$1