How to use TCP/IP services while the system is down? Is there any way??

By putting the macine in Semi-Restricted State, we can achive this.

In restricted state, your controlling subsystem will also have a status of END, so you won't be able to restart TCP/IP. Although there may be a way to restart TCP/IP from restricted state without IPLing, I've found it easier to just IPL into restricted state with TCP/IP started, as I'm showing here. You can do that by performing the following steps.

1. Change your startup program name to *NONE so that you won't restart your user subsystems and programs when you IPL. Retrieve and print the name of your current startup program by running the following Display System Value command.

DSPSYSVAL SYSVAL(QSTRUPPGM) OUTPUT(*PRINT)

This provides a record of what the startup program value was before you changed it.

Now change the Startup Program (QSTRUPPGM) system value to *NONE by running the following Change System Value (CHGSYSVAL) command.

CHGSYSVAL SYSVAL(QSTRUPPGM) VALUE(*NONE)

This will ensure your user subsystems won't start after you IPL.

2. Type in the Change IPL Attributes command (command) and press F4 to prompt it.

CHGIPLA

Change the Start TCP/IP (STRTCP) parameter to *YES. This will start TCP/IP services when the machine IPLs.

Change the Start print writers (STRPRTWTR) parameter to *NO. This is mostly a precaution to prevent any system printers from starting.

Press ENTER to save your changes.

3. IPL and restart your system by running the following Power Down System (PWRDWNSYS) command.

PWRDWNSYS OPTION(*IMMED) RESTART(*YES)

After your system restarts, the system will not run your startup program. So your applications, Web site, interactive subsystems, QSNADS subsystem, etc., will not start.

However, since you designated that you want to start TCP/IP on your IPL (STRTCP IPL parameter = *YES), the QSYSWRK subsystem will start and any TCP/IP interfaces that are set to automatically start on an IPL will be active.

If you run a Work with Active Jobs command, you'll see that there will only be two non-system subsystems active: your controlling subsystem (QCTL), and the QSYSWRK subsystem. All TCP/IP functions are run out of QSYSWRK, and TCP/IP should be active on your system. You will be in the semi-restricted state you asked for.

To make sure your TCP/IP interfaces are active in semi-restricted state, you can view your TCP/IP interfaces from the green screen by running the following options.

Call the Configure TCP/IP menu by typing in the Configure TCP/IP (CFGTCP) command from the command line.
Take option 1, Work with TCP/IP Interfaces, off the menu that appears.
On the Work with TCP/IP Interfaces screen that appears, press F11 to make sure that your designated IP interface status is Active. If it isn't active, type 9=Start in front of the interface to start it.

At this point, you should be able to download PTFs and upgrades without having the rest of your application programs running. If you're not able to run a TCP/IP server that you need, run the following Start TCP/IP Server command to start the server.

STRTCPSVR SERVER(server_to_restart)

Restarting Your System
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After you've done your work and are ready to restart the system with your application programs running, do the following.

Change the startup program system value back to the program and library name of your startup program. Do this by typing in the following Work with System Value command and pressing 2=change in front of the system value.

WRKSYSVAL SYSVAL(QSTRUPPGM)

Put your system back into restricted state again by running the ENDSBS command

ENDSBS SBS(*ALL) DELAY(60)

Perform the following PWRDWNSYS command to IPL and restart your system. This will restart all your applications and put your system back into regular working order.

PWRDWNSYS OPTION(*IMMED) RESTART(*YES)