75bb332db
Denys Vlasenko
2010-12-06
Subject
add examples/var_service/README
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examples/var_service/README+54 -0
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| + | 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 |
| + | |
| + | env - PATH=... <other vars=...> runsvdir /var/service & |
| + | |
| + | from one of system startup scripts. (Google "man runsvdir" and "man runsv" |
| + | for more info about these tools). |
| + | |
| + | Some existing examples: |
| + | |
| + | 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 |
| + | or 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. |
| + | |
| + | 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 - |
| + | Uses var_service/dhcp_if's data (/var/service/dhcp_if/dhcp_if.out file) |
| + | 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 - |
| + | An *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 |
| + | (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. |
| + | |
| + | However, any dhcp/ppp/vpn or similar service can restart it anytime |
| + | when it senses the change in network configuration. |
| + | This even works while fw service runs: if dhcp signals fw to (re)start |
| + | while fw runs, fw will not stop after its execution, but will re-execute once, |
| + | picking up dhcp's new configuration. |
| + | This is achieved very simply by having |
| + | # 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. |
| + | |
| + | 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. |