For information I do this and it’s ok.
Thanks
nano /etc/init.d/mystart.sh
—————-
#!/bin/sh
mts-io-sysfs store mfser/serial-mode rs232
exit 0
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chmod a+x /etc/init.d/mystart.sh
ln -s /etc/init.d/mystart.sh /etc/rc3.d/S99mystart.sh
ln -s /etc/init.d/mystart.sh /etc/rc5.d/S99mystart.sh