9srv Manual Collection/plan9/boot(8) | 9srv Manual Collection/plan9/boot(8) |
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Once loaded, the kernel initializes its data structures and devices. It sets the two environment variables /env/cputype and /env/terminal to describe the processor. It then binds a place-holder file server, root(3), onto / and crafts an initial process whose sole function is to exec(2) /boot/boot, a binary which is compiled into root(3).
The command line passed depends on the information passed from boot ROM to kernel. Machines that boot directly from ROM (that is, most machines other than PCs) pass the boot line given to the ROM directly to boot.
On the PC, each line in the DOS file plan9.ini of the form name=value is passed to the boot program as an environment variable with the same name and value. The command line is
(The first argument is ignored by boot.) Boot must determine the file server to use and a method with which to connect to it. Typically this will name a file server on the network, or state that the root file system is on local disk and name the partition. The complete list of methods is given below.
Boot must also set a user name to be used as the owner of devices and all console processes and an encryption key to be used when challenged. Boot will prompt for these.
Method and address are prompted for first. The prompt lists all valid methods, with the default in brackets, for example:
A newline picks the default. Other possible responses are method or method!address. To aid in automatic reboot, the default is automatically taken on CPU servers if nothing is typed within 15 seconds.
The other interactions depend on whether the system is a terminal or a CPU server.
The user will also be prompted for a password to be used as an encryption key on each attach(5):
With most methods boot can now connect to the file server. However, with the serial line methods 9600 and 19200, the actual mechanics of setting up the complete connection are too varied to put into the boot program. Instead boot lets the user set up the connection. It prints a prompt on the console and then simulates a dumb terminal between the user and the serial line:
The user can now type at the modem to dial the number. What is typed depends on the modem and is beyond this discussion.
When the user types a control-D, boot stops simulating a terminal and starts the file system protocol over the serial line.
Once connected, boot mounts the root file system before / and makes the connection available as #s/boot for subsequent processes to mount (see bind(2)). Boot completes by exec(2)'ing /$cputype/init -t. If the -m option is given it is also passed as an option to init. If the environment variable init is set (via plan9.ini(8)), it is used as a command line to exec instead.
If the kernel has been built with the cache file system, cfs(4), the local disk partition /dev/sdXX/cache (where XX is a unit specifier) exists, and the root file system is from a remote server, then the kernel will insert a user level cache process between the remote server and the local namespace that caches all remote accesses on the local partition. The -f flag commands cfs to reformat the cache partition.
The key is used for mutual authentication of the server and its clients. The domain and id identify the owner of the key.
Once connected, boot behaves as on the terminal except for exec(2)'ing /$cputype/init -c.
Start kfs(4) with extra disk buffers:
Use an IP stack on an alternate ethernet interface with a static address and fixed file server and authentication server addresses.
(The bootargs line is split only for presentation; it is one line in the file.)
9srv Manual Collection/plan9/boot(8) | Rev: Fri Feb 15 22:45:32 GMT 2013 |