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#1 2017-11-27 10:01:24

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

runit as a process supervisor

Having reading the message on DNG from Steve Litt about process supervisors :-

https://lists.dyne.org/lurker/message/2 … d3.en.html

I was inspired to investigate for myself. This is not a recipe on how to use runit as your init system, but some notes on using runit as a stage 2 process supervisor.

Of the supervisors mentioned by Steve, only runit was available in the jessie repository so that is what I had a look at.

The set up on ascii is slightly different from jessie. On jessie when installed it all ready for running as a process supervisor. On ascii there is a separate package to install to set up this supervisory role. It would appear that the ascii version is more ready to be run as a replacement init.

On jessie :-

apt-get install runit

on ascii

apt-get install runit runit-sysv

When running

ps uaxf

runsvdir can be seen with space "....." for displaying log messages,
although it is not actually supervising anything yet.

The ascii installation seems to be missing some of the documetation at :-

file:///usr/share/doc/runit/html/

in that the info on the separate programs is missing, although the index.html
page does give the link to the author's pages :-

http://smarden.org/runit/

Also on ascii the directory /etc/service is a link to /etc/runit/default.

Once runit is installed, then comes the job of setting up some daemons to be supervised. They are set up in sub-directories of /etc/sv and when everything is ready a link is set up in /etc/service to the sub-directory in /etc/sv. At this point runsvdir should notice and start running the daemon.

I wanted something simple to start with and went for the display manager. This is very simple, although there is some scope for fun as this can crash X while you are finishing the set-up, so it is good to know what you need to do to finish things. One difference from sysv init is that the daemon should not run in the background, but should remain connected to stdin/stdout. In this case, it means NOT using the "-d" switch to the display manager.

While on jessie I am using "slim" with lxde, on ascii I am using "lxdm" with lxde with some components of lxqt.

There needs to be a file called "run" to run the daemon. Is also possible to set up logging, using svlogd. This uses a sub-directory called log and its own "run" file. The supplied examples show logs being written under the log sub-directory, that is, within the /etc filesystem. I was not too happy with this and set up a separate directory in /var Presumably you could log in /var/log, but I avoided that in case there was any interaction with logrotate, as svlogd looks after its own logs.

These are the steps I took to set up lxdm under runit on ascii :-

mkdir -p /var/svlogd/lxdm
adduser --system log
chown -R log /var/svlogd

cd /etc/sv
mkdir -p lxdm/log

cd lxdm
cat << EOF > run
#!/bin/sh
exec 2>&1
exec /usr/sbin/lxdm
EOF

cd log
cat << EOF > run
#!/bin/sh
exec chpst -ulog svlogd -tt /var/svlogd/lxdm
EOF

cd ..
chmod a+x run log/run

cd /etc/service
update-rc.d lxdm disable
ln -s /etc/sv/lxdm .

This failed to stop X, but was all set up, so I rebooted and it all just worked.
Looking at the output from ps :-

ps uaxf

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
...
root      2398  0.0  0.0   4212  1076 ?        Ss   15:44   0:00 runsvdir -P /etc/service log: ....................................................................
root      2405  0.0  0.0   4060   672 ?        Ss   15:44   0:00  \_ runsv lxdm
log       2406  0.0  0.0   4204   684 ?        S    15:44   0:00      \_ svlogd -tt /var/svlogd/lxdm
root      2407  0.0  0.0  43976  3604 ?        S    15:44   0:00      \_ /usr/sbin/lxdm-binary
root      2412  0.7  0.8 389104 71868 tty7     Ssl+ 15:44   0:27          \_ /usr/lib/xorg/Xorg :0 vt07 -nolisten tcp -novtswitch -auth /var/run/lxdm/lxdm-:0.auth
root      2425  0.0  0.0  49976  3256 ?        S    15:44   0:00          \_ /usr/lib/lxdm/lxdm-session
xxxxxx    2506  0.0  0.1 352720 13280 ?        Ssl  15:44   0:00              \_ /usr/bin/lxsession -s LXDE -e LXDE
xxxxxx    2559  0.0  0.0  11076   332 ?        Ss   15:44   0:00                  \_ /usr/bin/ssh-agent /usr/bin/startlxde
xxxxxx    2568  0.0  0.2 196632 16580 ?        S    15:44   0:01                  \_ openbox --config-file /home/xxxxxx/.config/openbox/lxde-rc.xml
xxxxxx    2573  0.1  0.3 910200 25920 ?        Sl   15:44   0:04                  \_ lxpanel --profile LXDE
xxxxxx    2788  0.0  0.0  36816  4668 ?        S    15:45   0:00                  |   \_ urxvt
xxxxxx    2789  0.0  0.0  39236  2636 ?        S    15:45   0:00                  |   |   \_ urxvt
xxxxxx    2790  0.0  0.0  18396  3468 pts/0    Ss   15:45   0:00                  |   |   \_ bash
xxxxxx    3668  0.5  0.5 327340 47736 pts/0    Sl   16:38   0:03                  |   |       \_ emacs runit
xxxxxx    3820  0.0  0.0  17656  2068 pts/0    R+   16:48   0:00                  |   |       \_ ps uaxf
xxxxxx    2990  0.0  0.4 374260 39964 ?        Sl   15:59   0:01                  |   \_ claws-mail
xxxxxx    3306  3.8  3.1 857764 252200 ?       Sl   16:21   1:02                  |   \_ palemoon
xxxxxx    2574  0.0  0.5 602248 47304 ?        S    15:44   0:00                  \_ spacefm --desktop

The log file, /var/svlogd/lxdm/current, is empty, unlike my slim set-up under jessie, where the log file has output from Xorg as it starts up.

The set-up for slim on jessie is the same, simply replacing the word "lxdm" with "slim" everywhere.

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#2 2017-11-27 11:02:40

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

Postfix

Running the display manager under runit was very straightforward. I also tried something more complex. As a domestic user I use an mail provider, GMX in my case. However, some system messages are generated locally for delivery to root. Although I recall that exim had been installed, I had earlier experience with postfix, so I had installed that instead and configured it for my requirements and it was working well. This was obviously a prime target for trying out under runit!

Looking at /etc/init.d/postfix I found nearly 1000 lines of impenetrable script. Whereas, I thought that the actual command to start postfix was :-

postfix start

and the actual daemon which is left running is "/usr/lib/postfix/master -w".

There is an example "run" file in the documentation and I tried it


#!/bin/sh
exec 1>&2
 
daemon_directory=/usr/lib/postfix \
command_directory=/usr/sbin \
config_directory=/etc/postfix \
queue_directory=/var/spool/postfix \
mail_owner=postfix \
setgid_group=postdrop \
  /etc/postfix/postfix-script check || exit 1

exec /usr/lib/postfix/master

This did not work well. It appeared to be checking every single file on the system and spotting that most were not owned by postfix! It also failed to run the daemon.

After some fiddling around I decided to try and keep it simple. Since "postfix start" does actually work, why not use it? Well it finishes and returns, which is not how runit works. I therefore set up a simple kludge, /etc/sv/postfix/run :-

#!/bin/sh
exec 1>&2

/usr/sbin/postfix start
while /usr/sbin/postfix status
do sleep 300
done

This does actually work! It also puts out a timestamp every 5 minutes in the log file.

I was not sure how things would work at shutdown, so I also set up a "finish" file. This is described as being executed if "run" stops.
/etc/sv/postfix/finish

#!/bin/sh
echo "calling /etc/sv/postfix/finish"
/usr/sbin/postfix stop

My hope is that if things are not shutdown properly, then this would tidy it all up! What I see in /var/log/mail.info is that the "master" daemon reports

postfix/master[2916]: terminating on signal 15
postfix/postfix-script[4443]: fatal: the Postfix mail system is not running

I think that the second line is saying that it can't stop as it isn't running.
Postfix does its own logging via syslog.

This simple set up seems to work ok, although not really in the spirit of runit!

Geoff

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#3 2017-11-27 20:10:57

fungus
Member
From: Any witch way
Registered: 2017-07-12
Posts: 391
Website

Re: runit as a process supervisor

This is too good of a contribution to get passed by:
https://sysdfree.wordpress.com/162

If you have any objections or want to make additions or edit please let me know.

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#4 2017-11-27 20:37:25

shevy
Member
Registered: 2017-08-16
Posts: 8

Re: runit as a process supervisor

Perhaps it could be polished up a little and then put onto a wiki if others want to follow up?

Admittedly I do not even know half of what has been written here so far. :-)

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#5 2017-11-28 09:27:14

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

fungus wrote:

If you have any objections or want to make additions or edit please let me know.

I am delighted that you find it useful. You are most welcome to use it.

Geoff

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#6 2017-12-04 15:04:17

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

Postfix and shutdown

There is some further documentation on runit at Gentoo :-

https://wiki.gentoo.org/wiki/Runit

including some example run scripts to be found at :-

https://gitlab.com/flussence/runit-scripts

thus they offer a postfix run file :-

https://gitlab.com/flussence/runit-scri … ostfix/run

I added in -d and corrected the paths. This does seem to work, although I notice that the sub-processes also have the -d flag.

#!/bin/sh -eu
/usr/sbin/postfix check
exec /usr/lib/postfix/master -d

Although "master" is in itself a process supervisor which looks after the various postfix programs. I think that this leads into questions that have been rising in my mind about shutdown. It is not very clear from the documentation how shutdown works if you only use runit as a process supervisor. As far as I can see the shutdown mechanism would use stage 3 of runit, if you were using runit as init. (As a supervisor, it is only stage 2).

With the run file running "master" directly (with the -d flag), as above, then on shutdown, /var/log/mail.info reports

postfix/master[2795]: fatal: master_sigdeath: kill process group: No such process
postfix/postfix-script[4380]: fatal: the Postfix mail system is not running

I think that the first line is "master" receiving a signal to stop. From /var/log/syslog I can sees that at shutdown ntpd (which is not under runit) exiting on signal 15 (TERM), so I would guess that that is what "master" has received. The second line above is probably from "finish", which is being executed after "run" finishes and is therefore correct! The man page for "shutdown" says that "All processes are first notified that the system is going down by the signal SIGTERM." I have assumed that any daemons run by SysV init would have their "K" scripts in /etc/rc0.d run at shutdown, although I can't currently find the documentation on that!

As the couple of daemons that I am trying under runit are not part of the SysV init, I assume that they just receive SIGTERM.

I am wondering whether the answer is to set up runit's stage 3 and somehow trigger it at shutdown, early enough that the daemons get the signal before they get a SIGTERM from elsewhere. The sample stage 3 file for Debian Sarge looks like this :-

#!/bin/sh
exec 2>&1

PATH=/command:/sbin:/bin:/usr/sbin:/usr/bin

LAST=0
test -x /etc/runit/reboot && LAST=6

echo 'Waiting for services to stop...'
sv -w196 force-stop /etc/service/*
sv exit /etc/service/*

echo 'Shutdown...'
/etc/init.d/rc $LAST

Since runit is not in charge, presumably running /etc/init.d/rc $LAST can be commented out. I also removed /command from the path.
Maybe, this stage 3 file could be triggered as K010runit in /etc/rc[06].d to get these daemons to stop cleanly.

cd /etc/rc0.d
ln -s /etc/runit/3 K010runit3
cd /etc/rc6.d
ln -s /etc/runit/3 K010runit3

Also I looked at whether it is possible have runsv catch the SIGTERM and handle it more gracefully. The man page for runsv tells how to customise control signals, so that for SIGTERM :-

/etc/sv/postfix/control/t could contain :-

#!/bin/sh
echo We have SIGTERM for postfix
/usr/sbin/postfix stop

so this should run for "terminate" and should also pick up the control signals for "down" and "exit", according to the man page for runsv.

This does run and appear in /var/svlog/postfix/current when I give the command

sv stop postfix

I reverted the postfix "run" file to the earlier one which uses the "postfix start" command and
with stage 3 being called from rc0.d and with control/t set up, then on shutdown I can see in /var/log/syslog :-

Dec  4 10:49:58 fluorine shutdown[4884]: shutting down for system halt
Dec  4 10:49:58 fluorine init: Switching to runlevel: 0
Dec  4 10:49:59 fluorine avahi-daemon[2600]: Got SIGTERM, quitting.
Dec  4 10:49:59 fluorine avahi-daemon[2600]: Leaving mDNS multicast group on interface xenbr0.IPv6 with address fe...
Dec  4 10:49:59 fluorine avahi-daemon[2600]: Leaving mDNS multicast group on interface xenbr0.IPv4 with address 19...
Dec  4 10:49:59 fluorine avahi-daemon[2600]: avahi-daemon 0.6.31 exiting.
Dec  4 10:50:00 fluorine postfix/master[2924]: terminating on signal 15
Dec  4 10:50:00 fluorine ntpd[2466]: ntpd exiting on signal 15
Dec  4 10:50:00 fluorine postfix/postfix-script[5281]: fatal: the Postfix mail system is not running
Dec  4 10:50:00 fluorine postfix/postfix-script[5289]: fatal: the Postfix mail system is not running
Dec  4 10:50:01 fluorine acpid: exiting
Dec  4 10:50:03 fluorine rsyslogd: [origin software="rsyslogd" swVersion="8.4.2" x-pid="2166" x-info="http://www.rsyslog.com"] exiting on signal 15.

I think that the 2 fatal messages are from "finish" and control/t being called after "master" has alread received SIGTERM, although the echo messages are not appearing in /var/svlogd/postfix/current, maybe svlogd has already been shutdown!

I can see that before I started trying runit and with postfix being started from SysV init, that on shutdown /var/log/mail.info reports :-

Nov 11 12:23:20 fluorine postfix/master[2909]: terminating on signal 15

So the set up with "runit" seems to produce more or less the same result as with SysV init. Setting up to run stage 3 from rc0.d and also setting up control/t does not appear to have any real effect on shutdown.

Geoff

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#7 2017-12-04 15:13:32

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

The actual file set up in /etc/sv/postfix looks like this :-

# find /etc/sv/postfix/ -name '*' -ls
651625    4 drwxr-xr-x   5 root     root         4096 Dec  3 17:41 /etc/sv/postfix/
652292    4 -rwxr-xr-x   1 root     root           71 Nov 24 14:31 /etc/sv/postfix/finish
652288    4 -rwxr-xr-x   1 root     root          121 Dec  3 17:41 /etc/sv/postfix/run
656409    4 drwxr-xr-x   2 root     root         4096 Dec  3 17:04 /etc/sv/postfix/control
661485    4 -rwxr-xr-x   1 root     root           66 Dec  3 17:04 /etc/sv/postfix/control/t
652295    4 drwxr-xr-x   3 root     root         4096 Dec  1 16:41 /etc/sv/postfix/log
661408    4 -rwxr-xr-x   1 root     root           58 Dec  1 16:38 /etc/sv/postfix/log/run
661426    4 drwx------   2 root     root         4096 Dec  4 13:48 /etc/sv/postfix/log/supervise
661458    0 -rw-------   1 root     root            0 Dec  1 16:41 /etc/sv/postfix/log/supervise/lock
661461    4 -rw-r--r--   1 root     root           20 Dec  4 13:48 /etc/sv/postfix/log/supervise/status
661477    0 prw-------   1 root     root            0 Dec  1 16:41 /etc/sv/postfix/log/supervise/ok
661728    4 -rw-r--r--   1 root     root            4 Dec  4 13:48 /etc/sv/postfix/log/supervise/stat
652424    4 -rw-r--r--   1 root     root            5 Dec  4 13:48 /etc/sv/postfix/log/supervise/pid
652426    0 prw-------   1 root     root            0 Dec  1 16:41 /etc/sv/postfix/log/supervise/control
652309    4 drwx------   2 root     root         4096 Dec  4 13:48 /etc/sv/postfix/supervise
654580    0 -rw-------   1 root     root            0 Nov 23 11:20 /etc/sv/postfix/supervise/lock
661489    4 -rw-r--r--   1 root     root           20 Dec  4 13:48 /etc/sv/postfix/supervise/status
661277    0 prw-------   1 root     root            0 Nov 23 11:20 /etc/sv/postfix/supervise/ok
661390    4 -rw-r--r--   1 root     root            4 Dec  4 13:48 /etc/sv/postfix/supervise/stat
661388    4 -rw-r--r--   1 root     root            5 Dec  4 13:48 /etc/sv/postfix/supervise/pid
656413    0 prw-------   1 root     root            0 Dec  3 17:17 /etc/sv/postfix/supervise/control

The supervise sub-directories are automatically set up by runsv.

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#8 2017-12-07 09:57:39

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

I spotted another method of hanging for a daemon (rpc.nfsd) that detaches (in the Gentoo info).
The README file for the rpc.nfsd "run" says :-
   

"rpc.nfsd is a "fake" service implemented using lock-wedging. Doing it this way allows sv stop rpc.nfsd to work, by stopping it in the finish script."

After it has started the daemon, which detaches, the run file then does this :-

exec chpst -L supervise/runlock chpst -l supervise/runlock true

The change process state program (chpst) uses the -L switch to open the file supervise/runlock for writing, and obtain an exclusive lock on it. It then runs another copy of chpst which similarly gets a lock on the same file and then runs and returns "true".
The difference is that -L will fail immediately if it cannot get the lock, while -l will wait until it can get the lock. This line will therefore hang until it gets "sv stop postfix", when it will terminate true so that "finish" will be executed, which is set up to actually stop postfix. This does work as described, once the control/t file was moved out of the way, which was by-passing killing off the "run" process. The normal shutdown proceedure continues as before.

The set up is now fairly simple as it is only necessary to set up "run" & "finish" along with the logging.

cd /etc/sv/postfix
cat << EOF > run
#!/bin/sh
exec 2>&1
echo "executing /etc/sv/postfix/run"
/usr/sbin/postfix start
exec chpst -L supervise/runlock chpst -l supervise/runlock true
EOF

cat << EOF > finish
#!/bin/sh
exec 2>&1
echo "calling /etc/sv/postfix/finish"
/usr/sbin/postfix stop
EOF

mkdir log
cat << EOF > log/run
exec chpst -ulog svlogd -tt /var/svlogd/postfix
EOF

chmod a+x run finish log/run

the part of the output of ps uaxf relating to the postfix daemon looks like this :-

root      2767  0.0  0.0   4100   696 ?        Ss   09:02   0:00  \_ runsv postfix
log       2768  0.0  0.0   4244   708 ?        S    09:02   0:00      \_ svlogd -tt /var/svlogd/postfix
root      2771  0.0  0.0   4104   652 ?        S    09:02   0:00      \_ chpst -l supervise/runlock true
root      2903  0.0  0.0  36168  3152 ?        Ss   09:02   0:00 /usr/lib/postfix/master -w
postfix   2904  0.0  0.0  38232  3884 ?        S    09:02   0:00  \_ pickup -l -t unix -u -c
postfix   2905  0.0  0.0  38280  3936 ?        S    09:02   0:00  \_ qmgr -l -t unix -u

Geoff

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#9 2017-12-11 10:46:12

Geoff 42
Member
Registered: 2016-12-15
Posts: 74

Re: runit as a process supervisor

Current state

across 2 machines, the following are running under runit :-

slim
lxdm
autofs
bluetoothd
wicd
postfix

For most of them it is simply the case of setting up a run file containing the command along with the flag to stop it from running as a daemon, but remain attached to stdin/stdout. With a few (lxdm) it is rather the case that you leave out the flag that causes it to become a daemon. It is probably a good idea to set up logging for most of them. It is only slightly more complex when the program really does want to run as a daemon, such as postfix.

There is the question of why the SysV init scripts are so complex. I think that these have evolved this way as they check that everything has been set up correctly and where possible put things in place that should be there. It is understandable that a general purpose distribution will want everything to just work out of the box. The price of this is perhaps that the mechanism becomes more complex. One of the complexities seems to be the setting up of a PID file. I think that this is necessary so that init is able to control the service, whereas this is probably not necessary under runit.

The services which I have set up do seem to be simpler, but it may be that they do actually work because they were originally set up under SysV init, which sorted out any problems!

If you are developing a new service or have one which is not set up for SysV init, then it may be easier to get it running under runit.

Geoff

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