swap
1. What is Swap
Swap, also known as virtual RAM, is used to support storing data in hard disk when physical memory (RAM) is full. Sometimes Swap is also used in parallel to increase cache capacity even if the physical memory is not used up yet.
This may cause wear and tear on your microSD card leading to a shorter drive lifespan! It is strongly recommended to enable swap functionality only when there is insufficient memory available!
The Duo 256M memory is relatively large, so the default firmware does not add a Swap partition and does not support the Swap function.
2. How to enable Swap on Duo
Use the latest system image
https://github.com/milkv-duo/duo-buildroot-sdk/releases
Execute the following two commands to activate swap
mkswap /dev/mmcblk0p3
swapon /dev/mmcblk0p3
then run free -h command to check if the swap is active (256M)
[root@milkv-duo]~# free -h
total used free shared buff/cache available
Mem: 28.8M 13.6M 9.1M 76.0K 6.1M 12.4M
Swap: 256.0M 0 256.0M
3. How to increase the size of the Swap partition
The default firmware size of the Swap partition is 256M. There are two methods to increase the Swap partition size
1). Modify SDK and recompile to generate a new firmware
You can modify the value of this size, and then recompile to generate the firmware
You can modify the size of the Swap partition in the configuration file used to create the image, and then recompile and generate firmware. The configuration file links corresponding to each firmware are as follows:
2). Directly modify using the fdisk command in Duo
By connecting to Duo through a serial cable or SSH, you can use the fdisk command to modify it. The principle involves deleting the existing swap partition and creating a new one with the specified size
Any modifications to the partitions can potentially lead to data loss. Before performing any partition operations, please make sure to back up your important data！
The following is the step-by-step command-line interactive method using fdisk. If you're not familiar with this method, a script-based approach is provided later, which can be executed once to complete the modification
The command-line interactive mode of fdisk
Entering the fdisk command will take you into the command-line interactive mode of fdisk
fdisk /dev/mmcblk0
By entering the p command, you can view the information of the current partition on the MicroSD Card. You will be able to see that the partition /dev/mmcblk0p3 used for swap is 256MB in size
Command (m for help): p
Disk /dev/mmcblk0: 15 GB, 15931539456 bytes, 31116288 sectors
486192 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytes
Device Boot StartCHS EndCHS StartLBA EndLBA Sectors Size Id Type
/dev/mmcblk0p1 * 0,0,2 16,81,2 1 262144 262144 128M c Win95 FAT32 (LBA)
/dev/mmcblk0p2 16,81,3 114,57,8 262145 1835008 1572864 768M 83 Linux
/dev/mmcblk0p3 114,57,9 146,219,10 1835009 2359296 524288 256M 0 Empty
Please make a note of the StartLBA (starting sector) value for /dev/mmcblk0p3, which is 1835009. We will need it later
To delete a partition, you need to execute the d command and then enter the partition number you want to delete. In this case, we want to delete /dev/mmcblk0p3, so you should enter 3
Command (m for help): d
Partition number (1-4): 3
To create a new partition, you can use the n command. When prompted, choose whether to create a primary or extended partition. Since we want to create a primary partition, enter p. Next, enter the partition number you want to create, which is 3 for /dev/mmcblk0p3
The following prompt First sector is required to enter the starting sector value of the new partition, which is the value 1835009 recorded above. You can see that this value is recognized by default in the prompt, so you can just press Enter without inputting it
Finally, you will be asked to input the size of the new partition. You can either enter the ending sector value or directly specify the size of the partition. For example, if you want to allocate 1GB, you can enter +1G according to the prompt
Command (m for help): n
Partition type
p primary partition (1-4)
e extended
p
Partition number (1-4): 3
First sector (1835009-31116287, default 1835009):
Using default value 1835009
Last sector or +size{,K,M,G,T} (1835009-31116287, default 31116287): +1G
Then execute the p command again to check the current partition status. You will see that /dev/mmcblk0p3 is now 1024M, which is equivalent to 1G
Finally, execute the w command to save the modifications and exit the fdisk interactive mode
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table
fdisk: WARNING: rereading partition table failed, kernel still uses old table: Resource busy
At this point, the partition modifications will not take effect until you execute the reboot command to restart the system or power cycle the device
To activate Swap, you can execute the following two commands in the Duo terminal
mkswap /dev/mmcblk0p3
swapon /dev/mmcblk0p3
Then run the command free -h to check if the swap has been enabled (1G, which is equivalent to 1024M)
The script-based approach for fdisk
Create a script file named swap_resize.sh in Duo, or create it on your PC and then upload it to Duo
The contents of the swap_resize.sh file, please note to modify +1G to the desired size
fdisk /dev/mmcblk0 <<EOF
p
d
3
n
p
3
+1G
w
EOF
fdisk -l /dev/mmcblk0
echo "----- resize /dev/mmcblk0p3 for swap completed -----"
Executing this script in Duo will automatically modify the size of the swap partition
sh swap_resize.sh
Similarly, you need to execute the reboot command to restart the system or power cycle the device for the changes to take effect. After that, you can activate Swap again
mkswap /dev/mmcblk0p3
swapon /dev/mmcblk0p3
Then run the command free -h to check if the swap has been enabled (1G, which is equivalent to 1024M)
[root@milkv-duo]~# free -h
total used free shared buff/cache available
Mem: 28.8M 13.8M 8.2M 76.0K 6.8M 12.3M
Swap: 1024.0M 0 1024.0M
