4.7 KiB
System overview
Synit uses the Linux kernel as a hardware abstraction and virtualisation layer.
All processes in the system are arranged into a supervision tree, conceptually rooted at the system bus (NB. not at PID 1).
(Example)
+----------------------------------+
|Root System Bus (syndicate–server)|
+----------------+-----------------+
|
+--------+--------+---------+----------+---------------+
| | | | | |
+--+--+ +---+---+ +--+--+ +----+----+ +---+---+ +-----+-----+
|init | |console| |udevd| |Network | |Wifi | |Session bus|
+-----+ |getty | +-----+ |Interface| |Daemon | ... +-----+-----+
+-------+ |Monitor | |(wlan0)| |
|Daemon | +-------+ |
+---------+ |
|
+----------+----------------------------+
| | |
+---+---+ +--+--+ +----+---+
|Browser| |Email| . . . |X Server|
+-------+ +-----+ +--------+
Here's an example of ps
output from a Synit prototype running on a mobile phone:
PID TTY STAT TIME COMMAND
1 ? Ssl 0:00 /sbin/synit-pid1
1034 ? Sl 0:00 /usr/bin/syndicate-server --inferior --config /etc/syndicate/boot
1045 ttyS0 Ss+ 0:00 \_ getty 0 /dev/console
1052 ? S 0:01 \_ /sbin/udevd --children-max=5
1113 ? Sl 0:11 \_ python3 /usr/lib/synit/interface-monitor
1129 ? S 0:00 \_ sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups
1286 ? S 0:00 \_ wpa_supplicant -Dnl80211,wext -C/run/wpa_supplicant -i wlan0
1287 ? S 0:00 \_ udhcpc -i usb0 -fR -s /usr/lib/synit/udhcpc.script
1390 ? S 0:00 \_ ntpd -d -n -p pool.ntp.org
1431 ? S 0:01 \_ python3 /usr/lib/synit/user-settings-daemon
1497 ? Sl 0:01 \_ python3 /usr/lib/synit/wifi-daemon
1516 ? S 0:00 \_ udhcpc -i wlan0 -fR -s /usr/lib/synit/udhcpc.script
1035 ? S 0:00 s6-log t s999999 n500 /var/log/synit
Boot process
The kernel first loads the stock PostmarketOS initrd
, which performs a number of important
tasks and then delegates to /sbin/init
.
/sbin/init = synit-init.sh
The synit-config
package overrides the usual contents of
/sbin/init
, replacing it with a short shell script, synit-init.sh
. This script, in turn,
takes care of a few boring tasks such as mounting /dev
, /proc
, /run
, etc., ensuring that
a few important directories exist, and remounting /
as read-write before exec
ing
/sbin/synit-pid1
.
For the remainder of the lifetime of the system, /sbin/synit-pid1
is the PID 1 init
process.
/sbin/synit-pid1
- Source code:
[synit]/synit-pid1/
- Packaging:
[synit]/packaging/packages/synit-pid1/
The synit-pid1
program starts by spawning the system bus
(syndicate-server
in the process tree above) and the program /sbin/synit-log
, connecting
stderr
of the former to stdin
of the latter.
It then goes on to perform two tasks concurrently: the first is the Unix
init
role, reaping zombie processes, and the second is
to interact with the system bus as an ordinary system service.
The latter allows the system to treat init
just like any other part of the system, accessing
its abilities to reboot or power off the system using messages and assertions in the system
dataspace as usual.
Even though synit-pid1
is, to the kernel, a parent process of syndicate-server
, it is
logically a child process.
/sbin/synit-log
- Source code:
[synit]/packaging/packages/synit-pid1/synit-log
This short shell script invokes the S6 program s6-log
to capture log
output from the system bus, directing it to files in /var/log/synit/
.