96f1d6b70
Denys Vlasenko
2016-12-25
Subject
Update to examples/var_service/README_distro_proposal.txt
Binary
No binary (build failed)
Architecture & Compiler Flags
—
Build Log
(log yok)
Commit Diff GitHub →
examples/var_service/README_distro_proposal.txt+21 -14
| @@ -98,10 +98,10 @@ It is not required that a specific clone should be used. Let evolution work. | |
| daemon: any long running background program. Common examples are sshd, getty, | |
| ntpd, dhcp client... | |
| - | service: same as "daemon" |
| + | service: daemon controlled by a service monitor. |
| service directory: a directory with an executable file (script) named "run" | |
| - | which (usually) execs daemon (possibly after some preparatory steps). |
| + | which (usually) execs some daemon, possibly after some preparatory steps. |
| It should start it not as a child or daemonized process, but by exec'ing it | |
| (inheriting the same PID and the place in the process tree). | |
| @@ -116,7 +116,7 @@ whose directories disappeared. | |
| supervisor: a tool which monitors one service directory. | |
| It runs "run" script as its child. It restarts it if it dies. | |
| - | It can be instructed to start/top/signal its child. |
| + | It can be instructed to start/stop/signal its child. |
| In daemontools package, it is called "supervise". In runit, it is called | |
| "runsv". In s6, it is called "s6-supervise". | |
| @@ -150,7 +150,9 @@ The less distros diverge, the easier users' lives are. | |
| System-wide service dirs reside in a distro-specific location. | |
| The recommended location is /var/service. (However, since it is not | |
| - | a mandatory location, avoid depending on it in your run scripts). |
| + | a mandatory location, avoid depending on it in your run scripts. |
| + | Void Linux wanted to have it somewhere in /run/*, and they solved this |
| + | by making /var/service a symlink). |
| The install location for service dirs is /etc/rc: | |
| when e.g. ntpd daemon is installed, it creates the /etc/rc/ntpd | |
| @@ -182,10 +184,14 @@ of bad things may happen. This may be worked around by various | |
| heuristics in service monitor which give new service a few seconds | |
| of "grace time" to be fully populated; but this is not yet | |
| implemented in any of three packages. | |
| + | This also may be worked around by creating a .dotdir (a directory |
| + | whose name starts with a dot), populating it, and then renaming; |
| + | but packaging tools usually do not have an option to do this |
| + | automatically - additional install stripting in packages will be needed. |
| Daemons' output file descriptors are handled somewhat awkwardly | |
| by various daemontools implementations. For example, for runit tools, | |
| - | daemons' stdout goes to wherever runsdir's stdout was directied; |
| + | daemons' stdout goes to wherever runsvdir's stdout was directied; |
| stderr goes to runsvdir, which in turn "rotates" it on its command line | |
| (which is visible in ps output). | |
| @@ -236,11 +242,11 @@ there is no guarantee in which order commands are sent to them. | |
| If DIR has no slash and is not "." or "..", it is assumed to be | |
| relative to the system-wide service directory. | |
| - | The "svok DIR" tool exits 0 if service is running, and nonzero if not. |
| + | [Currently, "svc" exists only in daemontools and in busybox. |
| + | This proposal asks developrs of other daemontools implementations |
| + | to add "svc" command to their projects] |
| - | The "svstat DIR1 DIR2..." prints one human-readable line for each directory, |
| - | saying whether supervise is successfully running in that directory, |
| - | and reporting the status information maintained by supervise. |
| + | The "svok DIR" tool exits 0 if service is running, and nonzero if not. |
| Other tools with different names and APIs may exist; however | |
| for portability scripts should use the above tools. | |
| @@ -253,15 +259,16 @@ depending on the distro) its files to the "live" service directory, | |
| whereever it is located on this distro. | |
| Removal of the service should be done as follows: | |
| - | svc -d DIR [DIR/log], then remove the service directory |
| - | (this makes service monitor SIGTERM per-directory supervisors |
| - | (if they exist in the implementation)) |
| + | svc -d DIR [DIR/log], then remove the service directory: |
| + | this makes service monitor SIGTERM per-directory supervisors |
| + | (if they exist in the implementation). |
| Implementation details | |
| - | Top-level service monitor program name is not standardized. |
| - | [svscan, runsvdir, s6-svscan ...] |
| + | Top-level service monitor program name is not standardized |
| + | [svscan, runsvdir, s6-svscan ...] - it does not need to be, |
| + | as far as daemon packagers are concerned. |
| It may run one per-directory supervisor, or two supervisors | |
| (one for DIR/ and one for DIR/log/); for memory-constrained systems | |