Site Tools


USB formatting with swap partition

It is highly advisable to make some form of permanent storage available to Tomato. A swap partition can prevent several types of insufficient RAM symptoms, such as system instability, failing processes, and in very severe cases, even spontaneous reboots. All this will depend largely on the network load and on Tomato's configuration. Some functions require much more RAM than others, and higher network traffic will put more load on the router and require more RAM than lower traffic. USB is an excellent candidate for providing swap space.

Assuming you are using either an ARM build or a MIPS build with USB support, it is assumed you have already have USB support enabled.

For this example I'm using a 16GB USB 3.0 USB flash drive which is seen in the system as sda.

Automatic method

This assumes your drive device device name is sda ! If it's not, make sure to change the following commands consistent with your drive's device name.

The echo 1000M statement below defines the size of the swap partition (in MB). You may want to adjust that, according to your needs.

Then enter:

nvram set usb_automount="0"
(echo o; echo n; echo p; echo 2; echo ; echo 1000M; echo t; echo 82; echo n; echo p; echo 1; echo ; echo ; echo w) | fdisk $device
mkfs.ext2 -L USB $partion
mkswap /dev/sda2
swapon /dev/sda2
mkdir /mnt/sda1 && mount /dev/sda1 /mnt/sda1
nvram set usb_automount="1"

Manual method:

From the Web interface, disable the Automount checkbox in the USB and NAS/USB Support menu.

Via SSH: delete any existing partitions:

fdisk /dev/sda


At this point your USB flash drive is unpartitioned. Now let's create the necessary partition table:




ENTER (default)

1000M (Essentially 1 GB out for swap)





ENTER (default)

ENTER (default)

l (to verify)

w (to save and exit fdisk)

At this point you should have two unformatted partitions on your USB flash drive:

sda1 ~14GB (fs-type ext2/3/4)
sda2 ~1GB (fs-type swap)

Now, let's format the partitions. NOTE: it is suggested you use ext2 for USB flash drives and ext3 for hard disks.

mkfs.ext2 -L USB /dev/sda1
mkswap /dev/sda2

Now, mount the partitions

swapon /dev/sda2
mkdir /mnt/sda1 && mount /dev/sda1 /mnt/sda1

You can now re-enable USB Automount on the USB and NAS menu.

Final setup

The USB flash drive is now formatted. Your USB and NAS page settings should look like this:

Under Attached Devices, you should see something similar to this:

To verify the swap partition is working well, select the Overview page, and you should see informatoin related to swap space:

usb_formatting_with_swap_partition.txt · Last modified: 2021/01/15 16:14 by hogwild