Services init and supervision with Runit
contribution 🔼
about 🔼
runit is a init scheme with service supervision .
project web page @
functional integration 🔼
runit is a program that will initiate services that a user wants to be running in his/her computer. Service we call a program that will be usefull during the whole period that our computer is operational. Simple examples are cron , display servers , web servers, file servers , email servers, game servers, etc. So in a sense after the unix-like operating system that is constantly in memory running the other programs that we want to be also permanent in memory and running are the services.
Now the services by default are not programs to be controlled by gui buttons. I guess because:
- they must start from the kernel without the sysadmin-user intervining
- since services are supposed to be part of the system interface presented to it's user either locally or remotely to other computers that means that ideally we want some automation in keeping things functional in case of some class of problems were human intervention is not necessarily
- since a desktop service is one of the possible services then obviously starting and controlling a system's service is happening outside the gui-space enviroment .
So an interface is needed that can be called by other programs and by the sysadmin .
runit claims offering a simpler and more reliable inteface to service initialization and supervision and also a better setup and maintaining of a clean state - enviroment.
NFS is nowdays inside the linux kernel and the Devuan Daedalus / nfs-kernel-server package contains an interface to the nfs inside the kernel. I dont know pros and cons but that move highlights the semantics of program -> service transition.
runit in the context of system start up 🔼
boot
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kernel
loads
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init scheme starts
related workflows 🔼
manage processes
manage packages
install runit 🔼
We may not have to install runit. Usually when installing devuan (!workflow link!) we choose our init system.
$ sudo apt-get install runit
offline help 🔼
$ cd /usr/share/doc/runit/*
deb package of runit contains man pages and html help files.
runit deb package 🔼
devuan pkginfo/runit @ , debian tracker @ ,
binaries 🔼
runsvdir 🔼
After linux boots at some point it starts runit which will start runsvdir. What does runsvdir do ? According to man pages:
runsvdir starts a runsv(8) process for each subdirectory, or symlink to a directory, in the services directory dir,and restarts a runsv(8) process if it terminates.At least every five seconds runsvdir checks whether the time of last modification, the inode, or the device, of the services directory dir has changed.If so, it re-scans the service directory, and if it sees a new subdirectory, or new symlink to a directory, in dir, it starts a new runsv(8) process.
If runit is running we see in the process tree that runsvdir is running: runsvdir -P /etc/service log So it monitors /etc/service directory and for each directory in /etc/service it starts runsv passing as argument that /etc/service/foo directory as argument. There must be a run script to start a certain service.
locations 🔼
locations / /etc/sv 🔼
/etc/sv - contains service directories for a collection of runit compatible services.
But what does a service directory contain ? A service directory contain small scripts that implement the project-runit's service control interface.
For definitive and detailed answers we look at $ man runsv. ( @ ) . Lets read a small excerpt to get the idea:
runsv switches to the directory service and starts ./run. If ./run exits and ./finish exists, runsv starts ./finish. If ./finish doesn't exist or ./finish exits, runsv restarts ./run.
Packages that are compatible with runit contains /etc/sv/servicename/* files .
$ apt-file -x search '/etc/sv.*$'
locations / /etc/service 🔼
/etc/service contains links to service directories (/etc/sv/*) of those services that we want to be running.
/etc/service is the directory monitored by runsvdir. So links to /etc/sv files must be created here in order for runit and runsvdir to see a service and control it.The /etc/service directory contains a series of soft links representing the processes currently managed by runit. So /etc/sv contains service's control inteface scripts, /etc/service contains the actively managed services.
locations / /etc/runit/runsvdir 🔼
/etc/runit/runsvdir
install , remove a service 🔼
By install we mean making a service's runit control scripts (run,
managing running services 🔼
pre: we assume that in our computer runit is running.
manage running services / list running services 🔼
$ sudo sv status /etc/service/*
Since /etc/service contain links to the runit-control interfaces of runit-compatible installed services and since that location is by default monitored by runsvdir then by simply listing it's contents we could see the services that we want to be running. Better by passing as argument to sv status that location we can see what of those services is really running.
manage running services / using sv 🔼
sv is a program that can be used to send commands through the runsv, and to query status informations about a service. These are the requests that sv can make to a runsv-controlled running service:
$ sudo sv status foo-srv-dir / where foo-svr-dir is the service directory name that
/ identifies a runit-controllable service.
$ sudo sv up foo-srv-dir
$ sudo sv down foo-srv-dir
$ sudo sv once foo-srv-dir
$ sudo sv exit foo-srv-dir
find runit compatible services in Devuan 🔼
pre: pkg/apt-file installed and updated.
$ apt-file -x search '/etc/sv.*$'
check runit state 🔼
$ cat /proc/1/comm
If runit is running in our system will could see it in our process tree on the top.
$ pstree
runit─┬─dhclient
└─runsvdir─┬─2*[runsv]
├─7*[runsv───getty]
├─runsv─┬─dbus-daemon
│ └─svlogd
├─runsv─┬─dhclient
│ └─svlogd
├─runsv─┬─sshd─┬─sshd───sshd───bash───tmux: client
│ │ └─sshd
│ └─svlogd
├─runsv───cron
├─runsv───elogind
├─runsv───rsyslogd───3*[{rsyslogd}]
├─runsv─┬─exim4
│ └─svlogd
└─runsv───sleep
We see running : runit , runsvdir , runsv
how runit works 🔼
That diagram's creator is unknown .
kernel
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1|
.--- /etc/runit/reboot ---. init 14
,---| 2 |<--- runit-init <---- init 0|6
| -- /etc/runit/stopit -- |
| 13 |
'------------------------------------> 3|
.-----> runit
| |
| |
.---<---------<----+-------->---------.
| | | |
4| | 6| 10|
runit/1 | runit/2 runit/3
| | | |
5| | 7| 11|
start things | runsvdir sv
| | | |
| | 8| |
-->--| runsv /var/service/*
| | |
| | 12|
| .../current/* stop things
| | |
| | |
| start things |
| monitor things |
| restart things |
| | |
| 9| |
---<-----------<---------'