Fix Multiple GNUton Mount Points

[ExtremeFiretop]

Issue reported by scootertramp on snbforums here: https://www.snbforums.com/threads/backupmon-v1-10-2-2026-may-24-backup-restore-your-router-jffs-nvram-external-usb-drive-encrypt-cifs-smb-nfs-available-in-amtm.93052/post-994663

The problem appears to be caused by multiple MerlinAU startup processes... such as "startup", "addCronJob", and "postUpdateEmail" running at the same time and reaching the GNUton webs_update.sh patch logic before being properly serialized. This created a race condition where processes shared temporary files, moved the same files, and sometimes stacked multiple bind mounts on /usr/sbin/webs_update.sh.

Below is an example of me recreating the problem using the following command:
sleep 5; /jffs/scripts/MerlinAU.sh startup & /jffs/scripts/MerlinAU.sh addCronJob & wait

Here was the result of that command:

BEFORE:

Admin@RT-AX92U-5EB0:/tmp/home/root# df -h
Filesystem                Size      Used Available Use% Mounted on
ubi:rootfs_ubifs         69.4M     64.4M      5.1M  93% /
devtmpfs                199.5M         0    199.5M   0% /dev
tmpfs                   199.6M    384.0K    199.3M   0% /var
tmpfs                   199.6M      1.8M    197.8M   1% /tmp/mnt
mtd:bootfs                5.1M      4.2M    980.0K  81% /bootfs
mtd:data                  8.0M      3.2M      4.8M  40% /data
tmpfs                   199.6M      1.8M    197.8M   1% /tmp/mnt
tmpfs                   199.6M      1.8M    197.8M   1% /tmp
/dev/mtdblock9           63.0M      4.0M     59.0M   6% /jffs
/dev/sda1                 3.6G      1.0G      2.4G  30% /tmp/mnt/USB3
tmpfs                   199.6M      1.8M    197.8M   1% /www/index_style.css
tmpfs                   199.6M      1.8M    197.8M   1% /www/require/modules/menuTree.js
tmpfs                   199.6M      1.8M    197.8M   1% /www/state.js

TEST RUN:

Admin@RT-AX92U-5EB0:/tmp/home/root# sleep 5; /jffs/scripts/MerlinAU.sh startup & /jffs/scripts/MerlinAU.sh addCronJob & wait
mv: can't rename '/jffs/addons/MerlinAU.d/logs/RT-AX92U_FW_Update_2026-06-10_15_45_54.log': No such file or directory
mv: can't rename '/jffs/addons/MerlinAU.d/logs/RT-AX92U_FW_Update_2026-06-10_15_45_54.log.SAVED.TEMP.LOG': No such file or directory
mv: can't rename '/jffs/addons/MerlinAU.d/webs_update.sh.GNUTON.DL.TMP': No such file or directory
mv: can't rename '/jffs/addons/MerlinAU.d/webs_update.sh.GNUTON': No such file or directory

AFTER:

Admin@RT-AX92U-5EB0:/tmp/home/root# df -h
Filesystem                Size      Used Available Use% Mounted on
ubi:rootfs_ubifs         69.4M     64.4M      5.1M  93% /
devtmpfs                199.5M         0    199.5M   0% /dev
tmpfs                   199.6M    384.0K    199.3M   0% /var
tmpfs                   199.6M      1.8M    197.8M   1% /tmp/mnt
mtd:bootfs                5.1M      4.2M    980.0K  81% /bootfs
mtd:data                  8.0M      3.2M      4.8M  40% /data
tmpfs                   199.6M      1.8M    197.8M   1% /tmp/mnt
tmpfs                   199.6M      1.8M    197.8M   1% /tmp
/dev/mtdblock9           63.0M      4.0M     59.0M   6% /jffs
/dev/sda1                 3.6G      1.0G      2.4G  30% /tmp/mnt/USB3
tmpfs                   199.6M      1.8M    197.8M   1% /www/index_style.css
tmpfs                   199.6M      1.8M    197.8M   1% /www/require/modules/menuTree.js
tmpfs                   199.6M      1.8M    197.8M   1% /www/state.js
/dev/mtdblock9           63.0M      4.0M     59.0M   6% /usr/sbin/webs_update.sh
/dev/mtdblock9           63.0M      4.0M     59.0M   6% /usr/sbin/webs_update.sh

The fix was to place entire initialization (log cleanup and the GNUton download/compare/mount sequence) behind a dedicated blocking flock, while also using PID-specific temporary filenames and checking operation return codes.

Since the issue can no longer be reproduced, the concurrency race appears resolved to me?
Any ideas or suggestions you have or would like to share?