process for an individual service. Service directories themselves sit
inside a containing directory, and the runsvdir program supervises that
directory, running one child runsv process for the service in each
-subdirectory. Out of the box on Debian, for example, an instance of
-runsvdir supervises services in subdirectories of /var/service/.
+subdirectory. A typical choice is to start an instance of runsvdir
+which supervises services in subdirectories of /var/service/.
If /var/service/log/ exists, runsv will supervise two services,
and will connect stdout of main service to the stdin of log service.
and in many cases you also want to babysit them.
They present a case where different services need to control (start, stop,
-restart) eact other.
+restart) each other.
var_service/dhcp_if
This is an example of service with has a "finish" script. If downed ("sv d"),
"finish" is executed. For this service, it removes DHCP address from
-the interface.
+the interface. This is useful when ifplugd detects that the the link is dead
+(cable is no longer attached anywhere) and downs us - keeping DHCP configured
+addresses on the interface would make kernel still try to use it.
var_service/zcip_if
Zeroconf IP service: assigns a 169.254.x.y/16 address to interface "if".
-This allows to talk to other divices on a network without DHCP server
+This allows to talk to other devices on a network without DHCP server
(if they also assign 169.254 addresses to themselves).
var_service/ifplugd_if
var_service/supplicant_if
Wireless supplicant (wifi association and encryption daemon) service for
-inteface "if".
+interface "if".
var_service/fw
+"Firewall" script, although it is tasked with much more than setting up firewall.
+It is responsible for all aspects of network configuration.
+
This is an example of *one-shot* service.
It reconfigures network based on current known state of ALL interfaces.
One-shot-ness of this service means that it shuts itself off after single run.
IOW: it is not a constantly running daemon sort of thing.
It starts, it configures the network, it shuts down, all done
-(unlike infamous NetworkManagers which sit in RAM forever, doing hell knows what).
+(unlike infamous NetworkManagers which sit in RAM forever).
However, any dhcp/ppp/vpn or similar service can restart it anytime
when it senses the change in network configuration.
# Make ourself one-shot
sv o .
at the very beginning of fw/run script, not at the end.
+
Therefore, any "sv u /var/run/service/fw" command by any other
script "undoes" o(ne-shot) command if fw still runs, thus
runsv will rerun it; or start it in a normal way if fw is not running.
+This mechanism is the reason why fw is a service, not just a script.
+
System administrators are expected to edit fw/run script, since
network configuration needs are likely to be very complex and different
for non-trivial installations.
var_service/ntpd
Examples of typical network daemons.
+
+
+ Process tree
+
+Here is an example of the process tree from a live system with these services
+(and a few others). An interesting detail are ftpd and vpnc services, where
+you can see only logger process. These services are "downed" at the moment:
+their daemons are not launched.
+
+PID TIME COMMAND
+553 0:04 runsvdir -P /var/service
+561 0:00 runsv sshd
+576 0:00 svlogd -tt /var/log/service/sshd
+589 0:00 /usr/sbin/sshd -D -e -p22 -u0 -h /var/service/sshd/ssh_host_rsa_key
+562 0:00 runsv dhcp_eth0
+568 0:00 svlogd -tt /var/log/service/dhcp_eth0
+850 0:00 udhcpc -vv --foreground --interface=eth0
+ --pidfile=/var/service/dhcp_eth0/udhcpc.pid
+ --script=/var/service/dhcp_eth0/dhcp_handler -x hostname bbox
+563 0:00 runsv ntpd
+573 0:01 svlogd -tt /var/log/service/ntpd
+845 0:00 busybox ntpd -dddnNl -S ./ntp.script -p 10.x.x.x -p 10.x.x.x
+564 0:00 runsv ifplugd_wlan0
+598 0:00 svlogd -tt /var/log/service/ifplugd_wlan0
+614 0:05 ifplugd -apqns -t3 -u0 -d0 -i wlan0
+ -r /var/service/ifplugd_wlan0/ifplugd_handler
+565 0:08 runsv dhcp_wlan0_pinger
+911 0:00 sleep 67
+566 0:00 runsv unscd
+583 0:03 svlogd -tt /var/log/service/unscd
+599 0:02 nscd -dddd
+567 0:00 runsv dhcp_wlan0
+591 0:00 svlogd -tt /var/log/service/dhcp_wlan0
+802 0:00 udhcpc -vv -C -o -V --foreground --interface=wlan0
+ --pidfile=/var/service/dhcp_wlan0/udhcpc.pid
+ --script=/var/service/dhcp_wlan0/dhcp_handler
+569 0:00 runsv fw
+570 0:00 runsv ifplugd_eth0
+597 0:00 svlogd -tt /var/log/service/ifplugd_eth0
+612 0:05 ifplugd -apqns -t3 -u8 -d8 -i eth0
+ -r /var/service/ifplugd_eth0/ifplugd_handler
+571 0:00 runsv zcip_eth0
+590 0:00 svlogd -tt /var/log/service/zcip_eth0
+607 0:01 zcip -fvv eth0 /var/service/zcip_eth0/zcip_handler
+572 0:00 runsv ftpd
+604 0:00 svlogd -tt /var/log/service/ftpd
+574 0:00 runsv vpnc
+603 0:00 svlogd -tt /var/log/service/vpnc
+575 0:00 runsv httpd
+602 0:00 svlogd -tt /var/log/service/httpd
+622 0:00 busybox httpd -p80 -vvv -f -h /home/httpd_root
+577 0:00 runsv supplicant_wlan0
+627 0:00 svlogd -tt /var/log/service/supplicant_wlan0
+638 0:03 wpa_supplicant -i wlan0 -c /var/service/supplicant_wlan0/wpa_supplicant.conf -d
projects / oweals / busybox.git / blobdiff