mirror of
https://github.com/pygos/init.git
synced 2024-11-22 19:19:47 +01:00
72 lines
2.4 KiB
Markdown
72 lines
2.4 KiB
Markdown
|
# The Init Daemon
|
||
|
|
|
||
|
|
## Initial Ram Disk to Rootfs transition
|
||
|
|
|
||
|
|
After mounting the root filesystem, either the kernel or the initial ram disk
|
||
|
|
startup process is expected to exec the init program from the root filesystem.
|
||
|
|
|
||
|
|
At the current time, there is no support for re-scanning the service files
|
||
|
|
*yet*, so when init is started, the final configuration in `/etc/init.d` has to
|
||
|
|
be present. As a result, we currently cannot perform mounting of `/etc/` or
|
||
|
|
packing init into the initial ram disk and doing the rootfs transition.
|
||
|
|
|
||
|
|
Also, as a result of this, changing the service configuration requires a system
|
||
|
|
reboot to be effective.
|
||
|
|
|
||
|
|
This _will_ change in the future.
|
||
|
|
|
||
|
|
|
||
|
|
## Service Types and Targets
|
||
|
|
|
||
|
|
A service file has a *type*, specifying whether the service should be run once
|
||
|
|
or restarted when it terminates and a *target*, specifying when the service
|
||
|
|
should be run.
|
||
|
|
|
||
|
|
The *target* is similar to a runlevel in System V init. The init daemon
|
||
|
|
currently knows about the following targets:
|
||
|
|
|
||
|
|
* boot
|
||
|
|
* reboot
|
||
|
|
* shutdown
|
||
|
|
|
||
|
|
When `init` is run, it starts all the services for the `boot` target. From the
|
||
|
|
`boot` target it can transition to any other target and execute the services
|
||
|
|
for the specified target.
|
||
|
|
|
||
|
|
The `reboot` and `shutdown` targets cannot transition to any other target and
|
||
|
|
when invoked, cause initd to drop everything else it intended to do.
|
||
|
|
|
||
|
|
For the `reboot` and `shutdown` targets, respawn type processes are no longer
|
||
|
|
restarted when they terminate and once all services have been executed, the
|
||
|
|
`init` program performs a hard system reboot or power off.
|
||
|
|
|
||
|
|
The init program tries to capture the `CTRL+ALT+DELETE` key sequence (or its
|
||
|
|
local equivalent) and transitions to the reboot target if pressed.
|
||
|
|
|
||
|
|
|
||
|
|
## Service Configuration Rescan
|
||
|
|
|
||
|
|
TBD
|
||
|
|
|
||
|
|
|
||
|
|
## Control Socket and Signals
|
||
|
|
|
||
|
|
The `init` program catches the following signals:
|
||
|
|
|
||
|
|
* `SIGCHLD`
|
||
|
|
* `SIGINT`
|
||
|
|
* `SIGTERM`
|
||
|
|
|
||
|
|
The `SIGCHLD` handler implements standard process reaping. If a terminated
|
||
|
|
process belongs to one of the supervised services, the configured action is
|
||
|
|
taken (e.g. restarting it).
|
||
|
|
|
||
|
|
When `SIGINT` is caugth, `init` transitions to the `reboot` target. Similarly,
|
||
|
|
`SIGTERM` causes `init` to transition to the `shutdown` target.
|
||
|
|
|
||
|
|
|
||
|
|
For more complex tasks, `init` creates a control socket that the command line
|
||
|
|
tools included in this package can use. For the time being, the control socket
|
||
|
|
can only tell the init daemon to transition to the `reboot` or `shutdown`
|
||
|
|
target.
|