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diff --git a/examples/var_service/README b/examples/var_service/README index d096ad0..52dd781 100644 --- a/examples/var_service/README +++ b/examples/var_service/README @@ -1,50 +1,149 @@ -In many cases, network configuration makes it necessary to run several daemons: -dhcp, zeroconf, ppp, openvpn and such. They need to be controlled, -and in many cases you also want to babysit them. runsvdir is a good tool for this. -examples/var_service directory provides a few examples. It is meant to be used -this way: copy it somewhere (say, /var/service) and run something like + Daemontools and runit + +Tired of PID files, needing root access, and writing init scripts just +to have your UNIX apps start when your server boots? Want a simpler, +better alternative that will also restart them if they crash? If so, +this is an introduction to process supervision with runit/daemontools. + + + Background + +Classic init scripts, e.g. /etc/init.d/apache, are widely used for +starting processes at system boot time, when they are executed by init. +Sadly, init scripts are cumbersome and error-prone to write, they must +typically be edited and run as root, and the processes they launch do +not get restarted automatically if they crash. + +In an alternative scheme called "process supervision", each important +process is looked after by a tiny supervising process, which deals with +starting and stopping the important process on request, and re-starting +it when it exits unexpectedly. Those supervising processes can in turn +be supervised by other supervising processes. + +Dan Bernstein wrote the process supervision toolkit, "daemontools", +which is a set of small, reliable programs that cooperate in the +UNIX tradition to manage process supervision trees. + +Runit is a more conveniently licensed and more actively maintained +reimplementation of daemontools, written by Gerrit Pape. + +Here I’ll use runit, however, the ideas are the same for other +daemontools-like projects (there are several). + + + Service directories and scripts -env - PATH=... <other vars=...> runsvdir /var/service & +In runit parlance a "service" is simply a directory containing a script +named "run". -from one of system startup scripts. (Google "man runsvdir" and "man runsv" -for more info about these tools). +There are just two key programs in runit. Firstly, runsv supervises the +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/. -You can try or debug an individual service by running its SERVICE_DIR/run script. +If /var/service/log/ exists, runsv will supervise two services, +and will connect stdout of main service to the stdin of log service. +This is primarily used for logging. + +You can debug an individual service by running its SERVICE_DIR/run script. In this case, its stdout and stderr go to your terminal. You can also run "runsv SERVICE_DIR", which runs both the service and its logger service (SERVICE_DIR/log/run) if logger service exists. If logger service exists, the output will go to it instead of the terminal. -"runsvdir DIR" merely runs "runsv SERVICE_DIR" for every subdirectory in DIR. +"runsvdir /var/service" merely runs "runsv SERVICE_DIR" for every subdirectory +in /var/service. + + + Examples + +This directory contains some examples of services: + + var_service/getty_<tty> + +Runs a getty on <tty>. (run script looks at $PWD and extracts suffix +after "_" as tty name). Create copies (or symlinks) of this directory +with different names to run many gettys on many ttys. + + var_service/gpm + +Runs gpm, the cut and paste utility and mouse server for text consoles. + + var_service/inetd + +Runs inetd. This is an example of a service with log. Log service +writes timestamped, rotated log data to /var/log/service/inetd/* +using "svlogd -tt". p_log and w_log scripts demonstrage how you can +"page log" and "watch log". + +Other services which have logs handle them in the same way. -Some existing examples: + var_service/nmeter + +Runs nmeter '%t %c ....' with output to /dev/tty9. This gives you +a 1-second sampling of server load and health on a dedicated text console. + + + Networking examples + +In many cases, network configuration makes it necessary to run several daemons: +dhcp, zeroconf, ppp, openvpn and such. They need to be controlled, +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. + + var_service/dhcp_if -var_service/dhcp_if - controls a udhcpc instance which provides dhpc-assigned IP address on interface named "if". Copy/rename this directory as needed to run udhcpc on other interfaces (var_service/dhcp_if/run script uses _foo suffix -of the parent directory as interface name). When IP address is obtained or lost, -var_service/dhcp_if/dhcp_handler is run. It saves new config data to -/var/run/service/fw/dhcp_if.ipconf and (re)starts /var/service/fw service. -This example can be used as a template for other dynamic network link services -(ppp/vpn/zcip). - -var_service/ifplugd_if - -watches link status of interface if. Downs and ups /var/service/dhcp_if +of the parent directory as interface name). + +When IP address is obtained or lost, var_service/dhcp_if/dhcp_handler is run. +It saves new config data to /var/run/service/fw/dhcp_if.ipconf and (re)starts +/var/service/fw service. This example can be used as a template for other +dynamic network link services (ppp/vpn/zcip). + +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. + + 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 +(if they also assign 169.254 addresses to themselves). + + var_service/ifplugd_if + +Watches link status of interface "if". Downs and ups /var/service/dhcp_if service accordingly. In effect, it allows you to unplug/plug-to-different-network and have your IP properly re-negotiated at once. -var_service/dhcp_if_pinger - + var_service/dhcp_if_pinger + Uses var_service/dhcp_if's data to determine router IP. Pings it. If ping fails, restarts /var/service/dhcp_if service. Basically, an example of watchdog service for networks which are not reliable and need babysitting. -var_service/fw - -A *one-shot* service which reconfigures network based on current known state -of ALL interfaces. Uses conf/*.ipconf (static config) and /var/run/service/fw/*.ipconf + var_service/supplicant_if + +Wireless supplicant (wifi association and encryption daemon) service for +inteface "if". + + var_service/fw + +This is an example of *one-shot* service. + +It reconfigures network based on current known state of ALL interfaces. +Uses conf/*.ipconf (static config) and /var/run/service/fw/*.ipconf (dynamic config from dhcp/ppp/vpn/etc) to determine what to do. + 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 @@ -66,3 +165,10 @@ runsv will rerun it; or start it in a normal way if fw is not running. 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/ftpd + var_service/httpd + var_service/tftpd + var_service/ntpd + +Examples of typical network daemons. |