From DD-WRT Wiki
Sometimes you install things and want them to load on startup. Writing startup scripts is the way to go!
Here are three ways to get dd-wrt to run them automatically.
Another method to have scripts run at startup is to place them in the right folder, with the .startup extension. Read more at Script_Execution
 Web Interface Method of Loading Scripts onto Router
- Know how to use and access Web Interface
- Know the sequence of commands you'd like to run every startup
- (optional) test commands at the command line to ensure correct operation
- Using the Web Interface, goto the Administration tab.
- If available, go to the Command subtab, otherwise go to the diagnostics subtab.
- Type the commands you wish to run every startup into the Commands: dialog box (place each command on a newline using the enter key, and if the command isn't something that stops running after a moment, put a '&' after the command)
- Click the Save Startup button at the bottom of the page if you'd like the commands to save into the rc_startup variable (you may need to scroll). Save Firewall will save the commands into the rc_firewall variable.
 How it Works
What this does is save your string of commands to the rc_startup variable in flash memory (also known as an NVRAM variable). Since flash memory doesn't get erased on startup, your "startup script" will remain with every boot and will always execute.
 NVRAM Method
- Know how to access and use Telnet or SSH
- Know the command(s) you would like to run every startup
- (optional) Test commands for correct operation.
- Login to your router using Telnet/SSH
- To set the startup scripts, use the following:
nvram set rc_startup=" <command 1> <command 2> ... <command n> "
When you give the command nvram commit the rc_startup variable is saved in flash memory and will remain when you reboot.
A good trick for entering long scripts that, say you downloaded from the internet, is the Paste function of Windows Telnet.
At the telnet prompt enter:
nvram set rc_startup="
When it switches to the > prompt, copy the text from notepad or your web browser, or wherever your script is saved, then right-click the telnet logo at the top of the telnet window, and point to Edit, then click Paste. Voila! the entire script is typed out, with each command neatly placed on its own line. Now type the final " and hit enter to save.
 How it Works
When you issue the first command you'll notice the prompt change to a ">" From here on every line you type is added to the rc_startup variable. You are still technically typing on the same command line, even though you are using multiple lines When you type the final '"' and hit [Enter] you'll see the prompt change back and your first command has been executed. That is, your script has been added to the variable rc_startup.
At this point you can check the contents of rc_startup by issuing the command:
~ # nvram get rc_startup
 Tip: Automating the Web-Interface
For automating or testing the web interface, the free iMacros Firefox Add-On can be used. You can record and replay your activities inside the web interface. You can download it at https://addons.mozilla.org/firefox/3863/
 Shell Script Method
A way to do this is to create a shell script that calls other shell scripts as required.
Simple nvram scripts are fine for short scripts, but if you'd like to do a lot, or if you'd like to easily manage your startup programs, the best method is through using shell scripts.
Shell scripts make it easier to write long scripts that in turn wget executable files or scripts from the internet, or ipkg -d ram install, copy pre-made configuration files from the flash partition, etc., before finally running your program, and doing so on every startup.
This means you don't need to save as much stuff in router flash space (nvram, which is rather limited) but you can instead fill up the much more prevalent RAM without having to manually re-install and configure your program(s) on every reboot.
And, since every program gets its own script, removing a program from the next boot is as easy as deleting, moving, or renaming its startup script file.
- Know how to access and use Telnet or SSH
- Know the command(s) you would like to run at startup
- Know how to copy files to and from router using SCP, WinSCP or another method.
- Have jffs enabled and working properly.
- (Windows only) TextPad, Win32Pad, Notepad++ or another *nix friendly text editor. Not notepad
- (optional) Test your commands to ensure proper operation.
 Write the Shell Script
Write a shell script for each program you would like to run on startup.
your script should be a *.startup file
Shell scripts should look like this:
#!/bin/sh <command 1> <command 2> <command 3> ... killall <command n program name> <command n>
Because of something in the linux system, your shell script could end up being run periodically, and not just at boot (cron maybe??). I'm not a linux user, so I'm not entirely sure why. However, this does mean that you'll need to ensure that only 1 copy of your program <command n> is ever run at a time. The killall command ensures that <command n> isn't running more than once simultaneously. This assumes that all commands that appear in the script prior to <command n> exit immediately after executing (such as cp, wget, or iptables.)
Ex a script: kismet_server.startup
#!/bin/sh # Make the /tmp/usr/bin folder and move there mkdir /tmp/usr mkdir /tmp/usr/bin cd /tmp/usr/bin #copy the executable file from my home web server wget http://192.168.1.2/kismet_server #kill any previously-running instances of kismet_server killall -q kismet_server #execute kismet_server using /jffs/etc/kismet.conf as the configuration file. /tmp/usr/bin/kismet_server -n -f /jffs/etc/kismet.conf
 Save the Script
Save the script on the router in the /jffs/etc/config directory. You may need to create this directory. Do so either in WinSCP or in a shell (SSH or Telnet) using the mkdir command.
 Make the Script Executable
Making your script executable means changing the file rights to "700" Do this through WinSCP or with the command
~ # chmod 700 /jffs/etc/config/<scriptname>.startup
 Tell your scripts to load on startup, ipup or wanup
For more info on this see article Script Execution
 Samba client method
The drawback of jffs is the fact it doesn't work on some firmware versions and it is rather small. If you have a Samba or Windows server running on your LAN you could use the fabulous 'sambashare' option. This adds a vast amount of writable storage to your router, and it is possible to set an automatic startup script when the samba share mounts on boot. You can find the samba share options in the web interface under administration. If you set the startup script (as in Script Execution) option to startup.sh the actual script run after mounting will be /tmp/smbshare/startup.sh
See also the Samba Filesystem for details.