Hercules mainframe emulator

Network Interface

Hercules emulates various types of network connections. The easiest type to configure is the channel-to-channel (CTC) connection. To configure two type-3088 CTC devices at the addresses 0cc0 and 0cc1, you just need to add one line to the configuration file (Listing 2, line 34), and assign an address of 192.168.2.2 to the guest and 192.168.2.1 to the host. The HTML documentation explains the syntax for the device addresses in particular.

To launch Hercules, type the command:

hercules -f conf/ centos45.conf > hercules.log

Figure 2 shows the initial output at the Hercules console. Here, the critical message is HHCCT073I, which tells me that the tun0 network device is open. Unfortunately, the message isn't completely reliable because it depends on the permissions for hercifc; to be certain, you have to check the output from route -n and ifconfig (Listing 3).

Figure 2: The Hercules console showing the supported features on startup.

Both the routing table (line 4ff.) and the network configuration (lines 29-35) must have entries for the tun0 device.

Listing 3

Verifying the Network Configuration

01 [root@sirius:~] # route -n
02 Kernel IP routing table
03 Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
04 192.168.2.2     0.0.0.0         255.255.255.255 UH    0      0        0 tun0
05 ...
06 127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
07 [root@sirius:~] # ifconfig
08 eth0      ...
09
10 lo        ...
11
12 tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
13           inet addr:192.168.2.1  P-t-P:192.168.2.2  Mask:255.255.255.255
14           UP POINTOPOINT RUNNING  MTU:1500  Metric:1
15           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
16           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
17           collisions:0 txqueuelen:500
18           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

Using Hercules

The Hercules console is used to control the system. Hercules supports a large number of commands, the most important of which is ipl (initial program load), which initiates the boot process. The maxrates command is useful, too; it outputs the performance in MIPS (million instructions per second).

Hercules supports alternate consoles. Pressing the Esc key toggles between the line-oriented console shown in Figure 1 and the semi-graphic console shown in Figure 3. This view gives you the current performance data, and you can see the register values flash past.

Figure 3: The semi-graphic Hercules with its colorful console.

To run Hercules remotely, you also can use an http console (Figure 4), which the administrator must set up in the configuration file (Listing 2, lines 12-13). Also, you can set up username- and password-based authentication, but this does not change the fact that the http connection is insecure.

Figure 4: The clear-cut Hercules web console.

Installing zLinux

Mainframes support two system architectures: zLinux with 31 bits (s390) and zLinux with 64 bits (s390x). Only the addressing is 31 bits for the 31-bit variant; the data itself uses the full 32 bits.

If you are looking for a free 64-bit zLinux, you can go for either the ThinkBlue/64 Linux [3] or the newer CentOS 4.5 [4], which is the distribution I used for this article.

Debian offers a good alternative; the 31-bit architecture is maintained throughout the Debian releases. I will not cover the differences between the Debian and CentOS installations.

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