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By default, dnsmasq stores DHCP lease data in (volatile) RAM. This means that operations such as a reboot will erase the lease database, forcing a new one to be created. This could be inconvenient, since client devices might receive a new IP address after DHCP renewal. For dnsmasq to maintain its DHCP lease information, the router needs persistent storage, (such as USB).
There are currently two common methods for dealing with this.
The first method does not use scripting. The goal of the first method is to store the lease database on permanent storage.
dhcp-leasefile=/mnt/usb/dnsmasq/dnsmasq.leases
The second approach is to keep the lease database in its default location and copy it to permanent storage at “halt” time. It is later restored when the init process runs during boot.
For example, in the Scripts menu, in the Init field, enter:
[ -f /mnt/usb/dnsmasq.leases ] && { sort -b -k 2 -u -z /tmp/var/lib/misc/dnsmasq.leases > /tmp/dnsmasq.tmp1 sort -b -k 2 -u -z /mnt/usb/dnsmasq.leases > /tmp/dnsmasq.tmp2 diff -a /tm kill -HUP `ps | grep rm /tmp/dnsmasq.tmp1 rm /tmp/dnsmasq.tmp2 }
In the same menu, in the Halt field, enter:
cp -f /tmp/var/lib/misc/dnsmasq.leases /mnt/usb/dnsmasq.leases
The second method can be used with any storage, including JFFS. included, where for USB (only) an alternative is to performed the save/copy within the Run after mounting/Run before unmounting on the USB page instead than the generic script section.